1993 TrasSport 3.8L Quad Driver Codes 26 and 56

[Jeffrv]

Here is something I came across on the net, not sure if you have already done the test, or if it might be of some value to you https://easyautodiagnostics.com/gm/4...-valve-tests-1

[tinkering]

Originally Posted by Tech II

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 have ordered a Cardone remanufactured PCM from amazon.ca for $150.00 CAD. After testing all the wires and connections like I did, I am going to throw some money at it. I am losing patience.
How often do the PROM(s) crap out?

[Jeffrv]

Proms seem to be quite robust, don't hear much problems with them as as a rule That being said, they can be damaged by electrical static discharge, critically important that you be thoroughly grounded to the PCM. They are also subject to physical damage while removing or installing, be careful doing that.
Did all these trouble codes show up all at once, or gradually one at a time over a period of time?

[tinkering]

Originally Posted by Jeffrv

Proms seem to be quite robust, don't hear much problems with them as as a rule That being said, they can be damaged by electrical static discharge, critically important that you be thoroughly grounded to the PCM. They are also subject to physical damage while removing or installing, be careful doing that.
Did all these trouble codes show up all at once, or gradually one at a time over a period of time?

I can't remember if all the codes showed up all at once or slowly gathered. That's been a long time, and I was driving the van for a long time with the eng light on.
I am going to be recovering for awhile now. I'm in the hospital with covid pneumonia at present. Parts are in though👌

[tinkering]

I am on the mend. We were part of the not quite as lucky; the china virus had me in the hospital for 10 days (no ICU).
The new computer did nothing for the Trans Sport. The engine light is still on.

It idles terribly rough still.
I don't know where to start now. I guess I have to go back to the beginning; read this whole thread again; double check stuff. Dang it.

[tinkering]

Here is my approach now.
The DTCs are 17,18,26,56.
I think I should work on the 17 and 18 codes first before the Quad Driver A and B codes 26 and 56.
DTC 17 Spark Reference Circuit could be related to the Crankshaft Sensor; It could be a defective Ignition Control Module too.
DTC 18 Cam/Crank Error is self explanatory.
I am going to replace the Cam Position Sensor firstly, because it is the easiest. Then the Crank Position Sensor if needed.
I saw on utube, a problem with the camshaft position sensor connector and the pigtail wires inside the harness, where oil had destroyed the insulation; they had been shorting. I will explore that too.
I need to check the wires, voltages, and connectors too.
It is idling rough intermittently; it starts poorly intermittently, kicks back on the starter sometimes.

All this should take care of DTCs 17 and 18, then I will carry on from there with DTCs 26 and 56, the Quad Driver codes.

What does the abreviation CKT mean in the GM service manual? ie. CKT 647. 'Connector'? I can't figure that out. Have to take a break from the manual��

[Blue Bowtie]

CKT - Circuit

[tinkering]

Do the codes clear on their own on that old OBD1 system, or do you have to clear them yourself? I changed out the camshaft position sensor but the light popped on again upon restart. I didn't have time to get a code readout to check if 1 of the 4 codes are out. Will update later.

[tinkering]

Ok, here is the update.
I don't know if the codes cancel on their own after repairs. I had the negative battery terminal undone so that might have cleared the codes. (Diagnostic trouble codes may be cleared by disconnecting the battery ground cable for at least 20 seconds. Reconnect negative battery cable and recheck codes to confirm the repair.)

After replacing the camshaft position sensor, codes 17 and 18 no longer are present. Hooooray!
Unfortunately codes 26 Quad Driver A and 56 Quad Driver B are still present.
I have a couple more possibilities to try that I found. See GM TransSport Service Manual Book 2 p. 6E3-A-48 etc. I will post again later, when I get that plan figured.

[tinkering]

In following the GM TransSport Service manual, and in tbe absence of a 'TECH 1' diagnostic tool can the Quad Driver tests be performed using a Digital Volt Meter DVM, or a multi meter, and test light. I have a feeling that most of the components can be tested without the TECH 1 toool? It looks rather abominable but doable with a little more patience.
I don't like giving up.

"Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
- Sherlock Holmes

[Blue Bowtie]

With the older GM ECMs the error codes are stored in memory for the last 50 engine start/run cycles. Once a fault has been repaired, the codes will erase after that occurs.

As for the quad driver outputs in the ECM, they are monitored for open circuits, shorted circuits, and voltages outside the allowable range. Those outputs operate things like the EVAP vent and purge solenoids, TCC lockup solenoid or other transmission shift solenoids, EGR vacuum solenoid, cooling fan relay, A/C clutch relay, and any other options. Shorted or open wiring, disconnected solenoids or relays, or solenoid/relay faults are common problems causing these codes.

Your factory wiring diagrams should indicate which loads are connected to QDM A (code 26) and QDM B (code 56).

[tinkering]

Originally Posted by Blue Bowtie

With the older GM ECMs the error codes are stored in memory for the last 50 engine start/run cycles. Once a fault has been repaired, the codes will erase after that occurs.

As for the quad driver outputs in the ECM, they are monitored for open circuits, shorted circuits, and voltages outside the allowable range. Those outputs operate things like the EVAP vent and purge solenoids, TCC lockup solenoid or other transmission shift solenoids, EGR vacuum solenoid, cooling fan relay, A/C clutch relay, and any other options. Shorted or open wiring, disconnected solenoids or relays, or solenoid/relay faults are common problems causing these codes.

Your factory wiring diagrams should indicate which loads are connected to QDM A (code 26) and QDM B (code 56).

Excellent summary. Thank you for that Blue Bowtie.
After I replaced the cam sensor and undid the neg battery terminal overnight, all the codes were erased when I did the first scan but 26 and 56 returned on subsequent scans.

I have already checked for continuity on all of the wires from the junction on the inner fender to the PCM. I will have to read back to see what other tests I completed back then. I am preparing myself to go through the whole list of component and circuit tests the best I can with test light and multimeter.
Yes, the GM Service Manual does have nice diagrams and text indicating the components controlled by each QDM. I will study that. This could be a nig pie to eat. I need to settle down and go one bite at a time.
Thanks again.

[tinkering]

I noticed something on the road test that could be pretty important here. When I stepped on the gas hard to kick it down, it felt like it didn't develop the power it normally does, then I noticed that the revs were reaching the yellow zone, but I was only doing 100 kph/ 60 mph. Could this indicate a fault with the transaxle Shift A or B Solenoid; or the TCC Apply Solenoid or TCC Brake? It makes sense somehow to me. What exactly do these solenoids do? I have to do some more reading in the manual but this at least might give me a place to start.

How does a guy attach images?

[Blue Bowtie]

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[tinkering]

Originally Posted by Blue Bowtie

Images must be hosted (stored) on an external site or web space. Those stored files can be linked into a post using html [img] tags, or by clicking the "Insert Image" icon above the message posting box.

I will try on the laptop. Can't do it on the phone.
I'd rather spend the time on the TransSport