1993 TrasSport 3.8L Quad Driver Codes 26 and 56

1993 TransSport 3.800
Has somebody got the correct list of code definitions for this van?
I did a forum search to no avail. I did a google search to no avail.
My old girl has codes 17,18,26,and 56.
It starts right up and runs fine but a few miles down the road starts to limp.
I love this old thing. I am going to clean 'er up and go around with 'er again for awhile.

Code 12 No distributor reference pulse (diagnostic test active)
Code 13 Oxygen sensor circuit open or no activity
Code 14 Engine coolant temp sensor error (high temp indicated)
Code 15 Engine coolant temp sensor error (low temp indicated)
Code 16 System voltage too low
Code 17 Camshaft position sensor error
Code 21 Throttle position sensor error (signal high)
Code 22 Throttle position sensor error (signal low)
Code 23 Intake air temp sensor error (low temp indicated)
Code 24 Vehicle speed sensor error (open circuit or no activity)
Code 25 Intake air temp sensor error (high temp indicated)
Code 26 Quad Driver Module (QDM A) error
Code 28 Auto transmission range pressure switch error
Code 31 Wastegate solenoid circuit error
Code 31 Gear Position Switch (PRNDL) error
Code 32 Baro sensor circuit error / EGR circuit Error / MAP sensor signal open
Code 33 MAP sensor circuit error (signal high indicating low vacuum)
Code 34 MAP sensor circuit error (signal low indicating high vacuum)
Code 35 IAC problem or idle error
Code 36 MAF sensor error / 24x crankshaft position sensor circuit error / 4T60-E Shifting error
Code 37 TCC brake switch circuit error
Code 38 TCC brake switch circuit error
Code 39 Clutch switch circuit error / Torque converter clutch error
Code 41 Ignition control error / MEM-CAL error / C³I Cam Sensor Signal error
Code 42 Ignition bypass circuit error
Code 43 Knock sensor error
Code 44 Oxygen sensor error (lean condition indicated)
Code 45 Oxygen sensor error (rich condition indicated)
Code 46 Pass-Key II (VATS) system error - circuit out of freq range
Code 47 UART (serial data) circuit error
Code 51 PROM error / Incorrect MEM-CAL
Code 52 Fuel cal-pak incorrect or missing
Code 53 System voltage too high
Code 53 Digital EGR valve solenoid 1 error
Code 54 Fuel pump circuit low voltage / Digital EGR valve solenoid 2 error
Code 55 ECM error / Digital EGR valve solenoid 3 error
Code 56 Quad Driver Module (QDM B) error
Code 57 Boost control error
Code 58 Trans fluid temp sensor circuit error (low voltage) / VATS system error
Code 59 Trans fluid temp sensor circuit error (high voltage)
Code 61 A/C system performance
Code 63 Right bank O2 sensor circuit error / MAP sensor circuit signal voltage high (low vacuum indicated)
Code 64 Right bank O2 sensor lean exhaust indicated / MAP sensor circuit signal voltage low (high vacuum indicated)
Code 65 Right bank O2 sensor rich exhaust indicated
Code 66 A/C pressure sensor circuit error (low pressure indicated)
Code 67 A/C pressure sensor circuit error
Code 68 A/C clutch relay circuit error (shorted to ground)
Code 69 A/C clutch relay circuit error (open circuit indicated) / A/C high pressure switch error
Code 70 A/C pressure sensor circuit error (high pressure indicated)
Code 71 A/C evaporator temp sensor circuit error (low temp indicated)
Code 72 VSS signal circuit error
Code 73 A/C evaporator temp sensor circuit error (high temp indicated)
Code 75 Digital EGR solenoid #1 circuit error
Code 76 Digital EGR solenoid #2 circuit error
Code 77 Digital EGR solenoid #3 circuit error
Code 79 Transmission fluid over temp
Code 80 Transmission component slipping
Code 82 3x crankshaft position sensor circuit error
Code 85 PROM error
Code 86 ECM Analog/Digital error
Code 87 EEPROM error (flash memory error)
Code 90 TCC error
Code 93 Transmission pressure control solenoid circuit error
Code 96 Transmission system voltage low
Code 98 Invalid PCM program
Code 99 Invalid PCM program

17 Camshaft Position Sensor error
Is the CSP Sensor easy to get at?
18 Where is code 18?
26 What is QuadDriver Module A?
56 What is QuadDriver Module B?

I just found a code definition list for 93 Trans Sport 3.8L at
https://www.troublecodes.net/gm/
Scroll way down the page.

17 Ignition control system, reference signal -circuit malfunction Wiring, poor connections, ICM, ECM

18 Camshaft position (CMP) sensor – circuit malfunction Wiring, CMP sensor, mechanical fault, ECM

26 Engine control module (ECM), quad driver/ output driver -circuit malfunction Wiring, ECM controlled components, ECM

56 Engine control module (ECM), quad driver/ output driver -circuit malfunction Wiring, ECM controlled components, ECM

Quad driver faults tend to lead towards an ECM......

Basically, a Quad driver commands up to 4 different circuits......if the quad driver gets the wrong data from a circuit, it sets a quad code.....

Not easy to diagnose....proper testing, is you isolate each circuit the quad driver runs.....you activate the circuit by grounding it with an ampmeter....you observe the current for up to 10 minutes, and if current goes out of range, you found a problem circuit.....

For example, suppose one of the circuits controlled is a relay...lets say the coil of the relay shorts out and now current is high.......the quad driver detects this, shuts down the circuit, and sets the code.....this is labor intensive, and most techs would just swap out an ECM from another vehicle(must be the same number, and if the PROM is different, have to swap them also), and if it took care of the problem, then they would just order an ECM, with the latest PROM for it.....

Like I said, more often than not, it's the ECM.......but with this time and mileage on it, it could be the circuit, a component in the circuit, or a bad connection also.....like I said, not easy to diagnose.....

Tech II,
That is Great info.
Where is access to the ECM? Under/behind the glovebox?

THios is the actual code list from the '93 tranport shop manual
www.avigex.ca/xport/3800codes.jpg
and dtc troubleshoot
www.avigex.ca/xport/dtc17.jpg
www.avigex.ca/xport/dtc18.jpg
www.avigex.ca/xport/dtc26.jpg
www.avigex.ca/xport/dtc55.jpg
www.avigex.ca/xport/dtc56.jpg
dtc56 usually refers to a failed section of the exhaust recirculating valve. The quad driver is not the culprit; it is the circuit that it controls that has failed and the fault is sensed at the driver level.

THios is the actual code list from the '93 tranport shop manual
www.avigex.ca/xport/3800codes.jpg

... and where is the ECM located?

It is behind the glove box, high on the firewall.
http://www.avigex.ca/xport/ecm.jpg
But all quad driver fails almost NEVER (in my case absolutely never) mean a fault of the drivers, but a fault of the elements or circuit controlled by the drivers. I never had to go to the ECM itself, excpt to its intermediate plug C111
http://www.avigex.ca/xport/IMG_0126.JPG
www.avigex.ca/xport/c111.jpg
www.avigex.ca/xport/c111b.jpg
on the engine side (firewall, above passenger wheel bowl) to take measurements by removing the plastic cover. C110 (same model) is also used as intermediate, near the passenger side headlight..but I never went to that one.
THe EGRvalve is the classic problem with DTC56, and purge canister valve with DTC26.
Some of DTC56 are related to transmisison control...but if all shifts are OK, then problem not transmission side.
To test EGR valve, pull plug from valve, D (from DTC55 page) is ground, A,B,C are the coils. I remember two coils are 25 ohms and one 12 ohms. It happens one of them is broken..infinite ohms. In one occasion the fail was with the plug contacts.

LMP, I have to disagree....those late 80's and early 90's PCM's were notorious for failures.....If you were lucky, a "tap test" would verify it....

But seeing how this PCM is 25 years old, chances are in it's lifetime it has been replaced....in fact, I would not be surprise if the label on it states "Reman".....

And as I stated before, I agree with you, every circuit would have to be checked out on the quad drivers to diagnose which could be labor intensive.....could be something as simple as a connection....but finding it is like a needle in the haystack....

And you would need wiring diagrams, a good meter, and the expertise to do the tests......only thing that saves your butt is a visual inspection, that shows something obvious....

THios is the actual code list from the '93 tranport shop manual
www.avigex.ca/xport/3800codes.jpg (http://www.avigex.ca/xport/3800codes.jpg)
and dtc troubleshoot
www.avigex.ca/xport/dtc17.jpg (http://www.avigex.ca/xport/dtc17.jpg)
www.avigex.ca/xport/dtc18.jpg (http://www.avigex.ca/xport/dtc18.jpg)
www.avigex.ca/xport/dtc26.jpg (http://www.avigex.ca/xport/dtc26.jpg)
www.avigex.ca/xport/dtc55.jpg (http://www.avigex.ca/xport/dtc55.jpg)
www.avigex.ca/xport/dtc56.jpg (http://www.avigex.ca/xport/dtc56.jpg)
dtc56 usually refers to a failed section of the exhaust recirculating valve. The quad driver is not the culprit; it is the circuit that it controls that has failed and the fault is sensed at the driver level.
Thanks LMP
That is invaluable information.
I need to take a look at that old EGR.

It is behind the glove box, high on the firewall.
http://www.avigex.ca/xport/ecm.jpg
But all quad driver fails almost NEVER (in my case absolutely never) mean a fault of the drivers, but a fault of the elements or circuit controlled by the drivers. I never had to go to the ECM itself, excpt to its intermediate plug C111
http://www.avigex.ca/xport/IMG_0126.JPG
www.avigex.ca/xport/c111.jpg (http://www.avigex.ca/xport/c111.jpg)
www.avigex.ca/xport/c111b.jpg (http://www.avigex.ca/xport/c111b.jpg)
on the engine side (firewall, above passenger wheel bowl) to take measurements by removing the plastic cover. C110 (same model) is also used as intermediate, near the passenger side headlight..but I never went to that one.
THe EGRvalve is the classic problem with DTC56, and purge canister valve with DTC26.
Some of DTC56 are related to transmisison control...but if all shifts are OK, then problem not transmission side.
To test EGR valve, pull plug from valve, D (from DTC55 page) is ground, A,B,C are the coils. I remember two coils are 25 ohms and one 12 ohms. It happens one of them is broken..infinite ohms. In one occasion the fail was with the plug contacts.
I will run the ohm tests on the EGR, and on the connector as you say.

I will see if there is a good looking EGR valve at the 'pick yerself' wreckers, and a Purge Canister valve too.



Is the purge canister valve right at the canister or...? How do you test it?

I remember the gas tank isn't venting properly; it builds up a vacuum which is very apparent when you open the gas cap when low on fuel. Is that related to the purge can valve code 26?

Thanks for the picture and diagrams of the black plastic PCM intermediate connector on the wheel well? Do you use that to test the QDrivers?

LMP, I have to disagree....those late 80's and early 90's PCM's were notorious for failures.....If you were lucky, a "tap test" would verify it....

But seeing how this PCM is 25 years old, chances are in it's lifetime it has been replaced....in fact, I would not be surprise if the label on it states "Reman".....

And as I stated before, I agree with you, every circuit would have to be checked out on the quad drivers to diagnose which could be labor intensive.....could be something as simple as a connection....but finding it is like a needle in the haystack....

And you would need wiring diagrams, a good meter, and the expertise to do the tests......only thing that saves your butt is a visual inspection, that shows something obvious....
I am going to leave the actual PCM til last because of the cost of the thing but I will see if there is a unit at the pick yerself that I can use to swap test the codes. I had to change one out on a similar year Buick once.


I'll do a bit of connection testing in the haystack but hopefully I don't have to get into any of the QDriver testing proceedures. It sounds like a big job. Thanks for that!

What are the most common component problems associated with codes 17 and 18?

THe EGRvalve is the classic problem with DTC56, and purge canister valve with DTC26.
Some of DTC56 are related to transmisison control...but if all shifts are OK, then problem not transmission side.
To test EGR valve, pull plug from valve, D (from DTC55 page) is ground, A,B,C are the coils. I remember two coils are 25 ohms and one 12 ohms. It happens one of them is broken..infinite ohms. In one occasion the fail was with the plug contacts.


The closest resistance readings of the 3 coils that I could find was 50 ohms on two and 25ohms on one. Does that sounds feasible? I remember changing the EGR valve and solenoid cluster 5 or 6 years ago.

There is an ugly transmission shift that happened a few times times on the highway (I think I started a thread on it way back when). When using the passing gear in the mountains it would pound back into cruise quite vehemently! I am going to change the vacuum modulator valve on the side of the transmission to see if that eliminates that occurrence.

Is there a transmission control module, a TCM or something similar?

This is the actual code list from the '93 tranport shop manual...
www.avigex.ca/xport/dtc18.jpg (http://www.avigex.ca/xport/dtc18.jpg)
...


Where is the crank/cam shaft position sensor located?

...the classic problem is purge canister valve with DTC26.

I found a bunch of cracked and collapsed rubber lines that I will change out.
I found the Purge Valve Solenoid (I think)... kinda top center of engine.

Is there a valve or any thing serviceable right on the Carbon (Vapor) Canister besides maybe a filter?
I found these parts online:
Vapor Canister https://www.thewrenchmonkey.ca/auto-parts/pontiac/trans-sport/1993/vapor-canister/
Vapor Canister Filter https://www.thewrenchmonkey.ca/auto-parts/pontiac/trans-sport/1993/vapor-canister-filter/
Vapor Canister Purge Solenoid https://www.thewrenchmonkey.ca/auto-parts/pontiac/trans-sport/1993/vapor-canister-purge-solenoid/

Vapor Canister Purge Valve https://www.thewrenchmonkey.ca/auto-parts/pontiac/trans-sport/1993/vapor-canister-purge-valve/

Quad driver faults tend to lead towards an ECM......

Basically, a Quad driver commands up to 4 different circuits......if the quad driver gets the wrong data from a circuit, it sets a quad code.....

Not easy to diagnose....proper testing, is you isolate each circuit the quad driver runs..........this is labor intensive, and most techs would just swap out an ECM from another vehicle(must be the same number, and if the PROM is different, have to swap them also), and if it took care of the problem, then they would just order an ECM, with the latest PROM for it.....

Like I said, more often than not, it's the ECM.......but with this time and mileage on it, it could be the circuit, a component in the circuit, or a bad connection also.....like I said, not easy to diagnose.....
Does this 1993 3.8 have an interchangeable PROM? Can I put the original PROM into a matching PCM from the wreckers?

Here's a neat site I found. This thread discusses some of the same material in this thread.
https://forums.aaca.org/topic/202125-1993-pontiac-tran-sport-van-pcm-prom/

Where is the crank/cam shaft position sensor located?
www.avigex.ca/xport/sensors.jpg

www.avigex.ca/xport/sensors.jpg (http://www.avigex.ca/xport/sensors.jpg)
Thanks for that great diagram.
Where can a guy get a download of that shop service manual?

..Where can a guy get a download of that shop service manual?
It is a hard copy manual...2 volumes.., about 2000 pages, that I had bought from GM when I bought the car. THe "user manual" contained the "order form" from GM. This is something that is no longer available in the digital world...
My website www.avigex.ca/xport contains a lot of scanned pages.
It used to be fully open to all a few years ago but the heavy traffic (specially from Russia..and I feared contamination ) ended up busting the allowed traffic on my website so I provide specific links on request now...

EDIT: exactly this one on ebay
https://www.ebay.com/itm/1993-Pontiac-Trans-Sport-Van-Shop-Manual-Set-Transport/360319050377?hash=item53e4b06289:g:oXUAAOSwuk1Z1VB 4:rk:2:pf:0
..and contrary to the description the seller gives, it covers both the 3.1 and the 3.8

It is a hard copy manual...2 volumes.., about 2000 pages, that I had bought from GM when I bought the car. THe "user manual" contained the "order form" from GM. This is something that is no longer available in the digital world...
My website www.avigex.ca/xport contains a lot of scanned pages.
It used to be fully open to all a few years ago but the heavy traffic (specially from Russia..and I feared contamination ) ended up busting the allowed traffic on my website so I provide specific links on request now...

EDIT: exactly this one on ebay
https://www.ebay.com/itm/1993-Pontiac-Trans-Sport-Van-Shop-Manual-Set-Transport/360319050377?hash=item53e4b06289:g:oXUAAOSwuk1Z1VB 4:rk:2:pf:0
..and contrary to the description the seller gives, it covers both the 3.1 and the 3.8
Thanks LMP!
I missed this reply so hense the late reply.
The link to your site says 'forbidden'. How do I access is, or do I?
😊
I'm just getting around to this work now so I have to review the whole thread but that is fine.

Yeah..as I stated in my previous post, "avigex.ca/xport" is not "open" access (for reasons I specified) ....just links for specific items like the one I gave for sensors..

It is a hard copy manual...2 volumes.., about 2000 pages, that I had bought from GM when I bought the car. THe "user manual" contained the "order form" from GM. This is something that is no longer available in the digital world...
EDIT: exactly this one on ebay
https://www.ebay.com/itm/1993-Pontiac-Trans-Sport-Van-Shop-Manual-Set-Transport/360319050377?hash=item53e4b06289:g:oXUAAOSwuk1Z1VB 4:rk:2:pf:0
..and contrary to the description the seller gives, it covers both the 3.1 and the 3.8
The ebay link eventually opened for me but I don't have $90 CAD including shipping, for that right now. I will keep mooching off of you:)

OK, I picked up some parts from the wreckers. I swapped out my original PROM into the wrecker ECM. On the road test the check engine light was going on and off for awhile. For awhile I thought we might have some positive results but after the engine warmed up it started to limp again, then I ran out of gas! I'm back at home now.
I think I remember that the EGR valve doesn't activate until the engine warms up. I'm going to swap it for the wrecker unit. Then I'm going swap the carbon canister and the purge valve.
I'll report back in awhile. 😊

Both the original and the wrecker ECMs give me the same scenario. I had to use the old PROM because the wrecker unit is out of a 93 Buick LeSabre. NO RESULTS: All Codes 17, 18, 26, 56 remained



I replaced the EGR Valve with a wrecker unit. NO RESULTS: Code 56 is still there.

An interesting thing though, is the resistance readings are quite different between the two EGR valves.
*The original unit reads 2 coils around 50 ohms and 1 around 25 ohms.
*The wrecker unit reads more like LPM said I should be finding; 2 coils around 25 ohms and 1 coil around 12 ohms. LPM, maybe I should use the wrecker unit but the other one is not that old??




RESULTS: I replaced the ICM (Ignition Control Module) with a wrecker unit. The tachometer is working again (It had quit ages ago)! So far it's running well, not going into 'limp' on the road test. NO MORE CODE 17 showing up. Hope it doesn't come back.



RESULTS: I replaced the CMP sensor (Cam Position Sensor) with a wrecker unit. NO MORE CODE 18 showing up. Hope it doesn't come back.




I have not located a used TVS (Canister Purge Valve) at the wreckers yet. I may have to order one from Amazon $40.00 CAD.

There should be a bench test for the purge valve though. How many volts 5, 10, 12, should I use to energize the solenoid to see if the port opens? I think it is either open or closed, no graduating positions, correct? I am hoping it's faulty and the cause of code 26.



There are 2 CTSs (Coolant Temp Switchs) that I found: *One is for the temp gauge; I think it's the one with 1 wire. *The other one (it has 2 wires) gives info to the ECM (I think) for other functions like the TVS and EGR etc.. THIS ONE HAS GOT TO BE THE MOST DIFFICULT TO ACCESS EVER!!! You have to remove both halves of the air cleaner housing and pipe, and STAND ON YOUR HEAD! If you have short fingers forget it, you have to start pulling the Idle Air Control stuff apart.

*Apparently there is a temperature/resistance chart for bench testing these sending units.
Does anybody have that info?


I am going to try all this stuff before I change out the canister with a wrecker unit I bought (This canister does not have a replaceable filter).

I'm starting to wonder if it might be a bad wire or connection somewhere; I pray not.

At some point in that era (maybe 1993, or 94-95) the canister purge solenoid went to a pulse width modulated (PWM) arrangement where the ECM would turn the solenoid on and off rapidly at part throttle, low load, to purge the EVAP canister. The solenoid is supplied by 12VDC and switched by the ECM. You can measure the resistance of the solenoid, and expect to read around 25-35Ω. You could also apply 12V to the solenoid and listen for the click when it moves.

As for the temperature sensor resistances, this table is still valid:

http://www.wwdsltd.com/files/CTS-MAT.gif

At some point in that era (maybe 1993, or 94-95) the canister purge solenoid went to a pulse width modulated (PWM) arrangement where the ECM would turn the solenoid on and off rapidly at part throttle, low load, to purge the EVAP canister. The solenoid is supplied by 12VDC and switched by the ECM. You can measure the resistance of the solenoid, and expect to read around 25-35Ω. You could also apply 12V to the solenoid and listen for the click when it moves.

As for the temperature sensor resistances, this table is still valid:

http://www.wwdsltd.com/files/CTS-MAT.gifTHANKS BBT! That is exactly what I was looking for!
I'll let you know the results.

At some point in that era (maybe 1993, or 94-95) the canister purge solenoid went to a pulse width modulated (PWM) arrangement where the ECM would turn the solenoid on and off rapidly at part throttle, low load, to purge the EVAP canister. The solenoid is supplied by 12VDC and switched by the ECM. You can measure the resistance of the solenoid, and expect to read around 25-35Ω. You could also apply 12V to the solenoid and listen for the click when it moves.

As for the temperature sensor resistances, this table is still valid:

http://www.wwdsltd.com/files/CTS-MAT.gif
The 1991 and 1992 Chilton Manual (all that I have:( indicates the canister purge valve is a TVS (Thermostatic Vacuum Switch). My 93 has the PWM design.

The purge valve (PWM design) reads around 37 or 38 ohms across the coil contacts at 70F. It's just above the high end of the spec range but is that good enough?
The solenoid energizes (opening the port) using a 9 volt battery. The valve holds vacuum indefinitely, and opens up sufficiently. If the resistance is good enough being just over the high end it looks like the purge valve is usable?

The purge valve readings are on the previous page. Please be sure to see them. Thanks

As for the temp sending units (CTSs):
*The one with the single contact (I think it controls the gauge) is 2810 ohms at 68F. The chart says they should be 3400 ohms at 70F.
*The double contact unit (I think might work with the ECM in controling the purge valve activation) reads 3040 ohms at 68F.
Both readings are somewhat low but considering a 10% +/- tolerance (brings it to 3060 ohms at 70F) are they good enough?
Is checking it at 70F good enough or do I need to check them at operating temperatures of 190, 200 etc.?

THis one from the transport shop manual. Same values
http://www.avigex.ca/xport/thermistor.jpg
IN fact, these thermistors are practially standard and used all over the car industry. My Kia Sorento , wife's Suzuki SX4....all the same
Values change rapidly across the temperature range, so minor differences at a specific temperature are irrelevant. ANd what you say about the purge solenoid valve is OK.
YOu can see both temp sensors on these diagrams, 1 for ECM, one for instrument panel
http://www.avigex.ca/xport/instrumentpanel1.jpg
http://www.avigex.ca/xport/tps.jpg

I checked the thermistors (CTSs) at round 40F too. I filled a sour cream tub with ice and water; cut a hole in the lid and threaded the CTS in so it reaches into the water.
I took the readings at around 35F-40F. They all seem to be changing with the temps, within reason as per the temp/resistance chart. So I am going out to put things back together.
If codes 26 and 56 remain I am thinking it is a wire or connector problem (I've done everything else I can think of) with the purge valve and EGR valve.
I'll get back.
thanks:lol2:

Went onto the highway test. The check engine light went out for a few minutes. I thought I had success but it started going on and off after awhile. Now it appears to be staying on again.
I picked up a new code, #44 oxygen sensor; exhaust appears to be lean.
... but back to the main focus, codes 26, and 56.
Code 26: I am swapping out the carbon can with a wrecker unit.
Code 56: I am going to clean the wrecker EGR unit. If that doesn't help I am going to put the old EGR back in. The next time to the wreckers I will pick up another EGR, one that looks newer.
Question: Are the Quad Drivers in the ECM or the PROM? I expect they are a part of the ECM. I am likely going to have to check the wires from the ECM to the EGR, and from the ECM to the purge valve but I only have a manual that covers 1991-1992 3.1L.
Do you have the chart/schematic I need to trace the wires out on my 1993 3.8L?
I can look to see if the reference voltage is arriving from the ECM, and stuff like that.

The quad drivers are hardware in the ECM, not the PROM or MEMCAL pack. A quad driver is an array of solid state output switches (four of them in a package) used to operate moderate load devices, such as the EGR solenoid, EVAP, indicator lights, transmission solenoids, etc. The ECM monitors them to see if they have overloads or open circuits. When the ECM detects a fault it sets a code. That can mean a failed driver in the ECM, or an open or shorted circuit or device connected to a driver.

The quad drivers are hardware in the ECM, not the PROM or MEMCAL pack. A quad driver is an array of solid state output switches (four of them in a package) used to operate moderate load devices, such as the EGR solenoid, EVAP, indicator lights, transmission solenoids, etc. The ECM monitors them to see if they have overloads or open circuits. When the ECM detects a fault it sets a code. That can mean a failed driver in the ECM, or an open or shorted circuit or device connected to a driver.
I'm barking up the right tree :)
I need a schematic or diagram that indicates wire colors, pin locations in the ECM connectors, and reference voltages so I can start narrowing things down. I can check ref voltage at the sensors and solenoids to check for short to ground or opens but need to know where to find them at the junction blocks, the ECM and it's connectors etc.. My manual doesn't cover 1993 TSport with the 3.8L engine. I assume the wiring will be different enough on the '91-'92 3.1L to let me down?
If the Qdrivers monitor the indicator lights, might a bad coolant temp gauge trip a code (or is that independant of the ECM circuits)? The temp gauge needle rides on 1/4 max; I've changed out that coolant temperature sensor, and I've replaced the thermostat with a 195F. It made no diff to the gauge; the needle never reaches up past the 1/4 position.
I found this link on YouTube. It is just about all I need except I would like a diagram to reference along with it.

Watch "How to test an electronic EGR valve (GM P1406 case study)" on YouTube
https://youtu.be/te_kapz-fj4
This guy ScannerDanner has a bunch of diagnostic videos on his YouTube channel, and a forum. He is teaming with info; talks a litte fast but it sinks in when reviewed. Fun to watch too.

Does the 93 TSport with 3.8L have an EVAP Vent Solenoid as well as the purge valve solenoid, or does one do the same job as the other?

Wire colors here, as in post #7
www.avigex.ca/xport/dtc26.jpg
www.avigex.ca/xport/dtc55.jpg
www.avigex.ca/xport/dtc56.jpg
looking for the pin ....
www.avigex.ca/xport/c111.jpg
www.avigex.ca/xport/c111b.jpg
www.avigex.ca/xport/IMG_0126.JPG
and the complete EVAP section
www.avigex.ca/xport/EVAP.pdf
about code 44, that is what made my TS unserviceable: it was an open O2 sensor heater .
see my thread here: http://www.automotiveforums.com/vbulletin/showthread.php?t=1151502
It came with a DTC13. It made the fuel burn spike up . I have bought a new O2 sensor but not installed yet....I use another car now.

You seem to find the sensors are pretty well in spec, so it would seem your thoughts about wiring issues would be the most likely cause. Two problem areas I have found in the past in my 95 TS are poor grounds, especially the major G200 ground located behind the drivers kick panel. As well, I have found engine vibration has caused intermittent internal breaks in wiring harness within the first 8 inches or so of the 2 engine to body 30 pin connectors. The body side is fixed, the engine side flexes, leading to intermittents. trace the wire from connector to device, and flex the harness as you test for continuity. It is a pain, I have had 2 circuits fail like this, and tracking down took some time
Good luck

... I have found engine vibration has caused intermittent internal breaks in wiring harness within the first 8 inches or so of the 2 engine to body 30 pin connectors.
I confirm this.

I confirm this.
Do you have a schematic of the other 30 pin connector too?:runaround: C110 I think. The one that is on more in front, above the carbon can.

Coming....
www.avigex.ca/xport/c110.jpg
www.avigex.ca/xport/c110a.jpg

Coming....
www.avigex.ca/xport/c110.jpg (http://www.avigex.ca/xport/c110.jpg)
www.avigex.ca/xport/c110a.jpg (http://www.avigex.ca/xport/c110a.jpg)
Thanks, these diagrams helped me immensely, even though they are for a
'VIN L' and mine is a 'VIN U'.

I did continuity checks on all the wires of the EGR and Canister Purge Solenoid, from the units right on through the C111 and C110 connectors to the 3 ECM connectors under the dash. I was disappointed to find zero opens.

With the ECM connectors still plugged in I was getting strange readings on what I think were the ground wires in the harnesses; some at 5 ohms, some at 25 ohms; it left me puzzled. Could there be a bad ground strap somewhere causing this, or...?

I need to go back and check continuity on the ground wires through to the ECM connectors, with the ECM connectors disconnected (I can't remember if I did that or not.) If there are no funny reading when unplugged then it might be resistance being noticed in the circuitry of the ECM.

I need to locate all the ground straps and re-fasten them.
This is dragging on but that is what wiring mysteries do.

I found a GM manual on eBay for $50 so I ordered it... waiting for shipment from USA.

I bought a download manual from eManualsonline.com but it was not the vehicle specific GM OEM manual that they advertised, so I have one now that covers a bunch of years but I'm not happy with that substitute they forced on me without even a partial refund. Be wary of that company.:runaround:

Thanks, these diagrams helped me immensely, even though they are for a
'VIN L' and mine is a 'VIN U'....
NOt sure why yours would be a VIN U ...in my book, VIN D is for the 3.1, VIN L for the 3.8. I know though that the platform for these models was known as the U body....

NOt sure why yours would be a VIN U ...in my book, VIN D is for the 3.1, VIN L for the 3.8. I know though that the platform for these models was known as the U body....
Which digit do you use again?
My 5th is a U, my 8th is an L.

Which digit do you use again?
My 5th is a U, my 8th is an L.

No reference to my serial number 1GMDU06L......

VIN D and VIN L are used in the shop manual ; VIN L for 3.8 and VIN D for 3.1 . AS I said, this body is known as U so possibly in the serial number U refers to the body, L to the engine type. I had not noticed before.

No reference to my serial number 1GMDU06L......

VIN D and VIN L are used in the shop manual ; VIN L for 3.8 and VIN D for 3.1 . AS I said, this body is known as U.
My mistake, it looks like they use the 8th digit. In that case, I too have a VIN L.

The PCM ground, as well, and many sensors, should be located on a ground stud under the ignition module. C heck there to see if any wires have broken or are corroded

35Ω is good for a "12V" solenoid for purge, TCC, and many of the other things the ECM would be controlling. Using Ohm's Law, that would translate to well under 2A at the 15V where the system normally operates. The quad driver sinking output transistors are commonly rated at 4A continuous, with heat sinks designed for that power dissipation.

The PCM ground, as well, and many sensors, should be located on a ground stud under the ignition module. C heck there to see if any wires have broken or are corroded

The ignition module is under (part of) the coil pack. Is the ground post connected to the underside of the coil pack unit? Is it easy to see or do you need to poke around under there with a mirror?

Yes, it is buried under the IM, you will need a mirror and flashlight to get a good look. If I remember, you will need a 15 MM deep socket to get it out

Yes, it is buried under the IM, you will need a mirror and flashlight to get a good look. If I remember, you will need a 15 MM deep socket to get it out
Excellent! I will have a look:smile:

I came across a page that listed all the ground connections but can't remember where.
I also need to go back and check to see what the other units are that both the Quad Drivers control. I can't remember where I saw that either. It might be in this thread otherwise in a manual.

You seem to find the sensors are pretty well in spec, so it would seem your thoughts about wiring issues would be the most likely cause. Two problem areas I have found in the past in my 95 TS are poor grounds, especially the major G200 ground located behind the drivers kick panel. As well, I have found engine vibration has caused intermittent internal breaks in wiring harness within the first 8 inches or so of the 2 engine to body 30 pin connectors. The body side is fixed, the engine side flexes, leading to intermittents. trace the wire from connector to device, and flex the harness as you test for continuity. It is a pain, I have had 2 circuits fail like this, and tracking down took some time
Good luck
1. I need to focus on the major G200 ground that you mentioned in post #38.

2. I forgot to do the 'flex test' when doing my continuity checks from the sensors to the engine side of the C110 and C111 30 pin connector blocks.
I had to plug everything back together so I could move the TS so I basically have to start over with this one.

3. I need to focus on the 'ground post' under the IM as in post #47

4. I need to locate the rest of the grounds.
Patience is a virtue. Thanks to you and the others for your virtuosity :icon16:

MY OFFICIAL GM 2 BOOK SHOP MANUAL ARRIVED TODAY!!!:lol:

Still hard at this one but getting no further. My new manual is giving me a bunch more ideas though.
Is the GM 'Tech 1' Scan Tool of any significant value to have? Where and how much is it?
Does a GM OBD I to OBD II adapter cord work (eBay)? I have a decent OBD II scanner and it would be handy to use it for my OBD I TSport.

Other things to look at for DTC 26 besides the Purge Solenoid, are the Puller Fan Relay, TCC Solenoids Connector, TCC Brake Switch. Any others?

Other things to consider for DTC 56 besides the EGR Valve, are TCC, improper shifting (there is that harsh shift when transaxel gears back up from kickdown passing at 60-75 mph). Could this do it? Any other related components to DTC 56?

I was checking 'Pin Drag' on the PCM connectors C1 and C2 and they are not uniform; I am wondering if that could be part of the trouble. What's the best tool to free the pin connectors from the socketsif that needs to be done?

Other things to consider for DTC 56...
Wiring continuity is still my prime suspect. I remember having tested continuity to the EGR valve right from the pins B1 , K3 at C111 and E2 at C110. WIth KEY ON and EGR plug connected, 12V is fed to all EGR coils and returns through the coils and wiring to all 3 contacts so you should measure 12V on each .
ABout transmission, if it shifts to all gears 1,2,3,4 then it is cleared from DTC 56 . If TCC applies then it is clear from DTC 26.

Tech 1 scanner is proprietary to GM...not on the market in as much as I know...

Wiring continuity is still my prime suspect. I remember having tested continuity to the EGR valve right from the pins B1 , K3 at C111 and E2 at C110. WIth KEY ON and EGR plug connected, 12V is fed to all EGR coils and returns through the coils and wiring to all 3 contacts so you should measure 12V on each .
ABout transmission, if it shifts to all gears 1,2,3,4 then it is cleared from DTC 56 . If TCC applies then it is clear from DTC 26.

Tech 1 scanner is proprietary to GM...not on the market in as much as I know...
I will check the EGR wiring again using a volt meter as you described. I will be sure to do a vigorous 'flex test' simultaneously.

Last road test I still had the MIL going out intermittently around 85 to 110 kph. I don't seem to get that when I rev the engine at a stand still, maybe up to 4000 rpm. Does that indicate anything to you?

It seems to always shift through all 4 gears. What indicator do I look for that the clutch is actually energizing, and it's not all just fluid coupling that's taking place? At what point does the clutch energize?

Last road test I still had the MIL going out intermittently around 85 to 110 kph. I don't seem to get that when I rev the engine at a stand still, maybe up to 4000 rpm. Does that indicate anything to you?...? At what point does the clutch energize?
THe egr valveS apply one after another or idependently under specific loads. At some point, the "faulty" EGR valve is not energised...hence the fault is not detected, hence no MIL. WHen conditions are such that THIS valve is tentativelky energised..and it does not, then you have the MIL. I have lived this condition too.
THe torque converter clutch can apply in 3rd and 4th gear. It applies only under light load and once applied in 4th gear, the RPM at 100 km/h will drop to 1600-1700. Without the TCC, rpm in same conditions will be over 2000.

THe egr valveS apply one after another or idependently under specific loads. At some point, the "faulty" EGR valve is not energised...hence the fault is not detected, hence no MIL. WHen conditions are such that THIS valve is tentativelky energised..and it does not, then you have the MIL. I have lived this condition too.
THe torque converter clutch can apply in 3rd and 4th gear. It applies only under light load and once applied in 4th gear, the RPM at 100 km/h will drop to 1600-1700. Without the TCC, rpm in same conditions will be over 2000.
I'm just getting back to this after being busy with other things. I can't blame it on the summer because we didn't have one🌞
I see a replacement EGR valve for $80 on Amazon.ca. I am tempted to throw it at the TransSport. Maybe there is a problem with the original and the wreckers EGR valves. I have spent so much time tracing and testing continuity all over the place without finding the culprit, maybe it's just the valve. I can go back to rechecking wires if the new valve doesn't pay off. Does this sound feasible to you, or is it just a feable attempt by a nearly defeated victim?🏳️

I'm just getting back to this after being busy with other things. I can't blame it on the summer because we didn't have one🌞
I see a replacement EGR valve for $80 on Amazon.ca. I am tempted to throw it at the TransSport. Maybe there is a problem with the original and the wreckers EGR valves. I have spent so much time tracing and testing continuity all over the place without finding the culprit, maybe it's just the valve. I can go back to rechecking wires if the new valve doesn't pay off. Does this sound feasible to you, or is it just a feable attempt by a nearly defeated victim?🏳️
I changed out the EGR valve with the new one, Standard brand. The light is still on but now it idles very rough when it slows down to idle rpm. Crumb

I changed out the EGR valve with the new one, Standard brand. The light is still on but now it idles very rough when it slows down to idle rpm. Crumb

The new gasket wasn't quite right. There was 3 gaskets with the new valve but none of them are correct.
I put the old gasket back on with tbe new valve. It's idling down correctly again but that light is still on. I have to check the codes again; maybe there is a different code keeping the light on now. Otherwise I have to go back amd do the testing LMP mentioned.