Service Engine Soon light question

[LTJGWorth]

I've got a 1992 GMC Safari V6 with 175000 miles. The van runs pretty good (idles a little rough at first and shifts a little sluggish when first started). The service engine soon light will come on after driving the thing for a while. It's never on when I first start it and it doesn't always come on. When it does come on, it's always after I have driven it for a while. What could cause that? O2 sensor? Something else?

[tableman]

It could be any one of the sensors, that fact that it goes away, after the van has been off and cooled down, it could be an O2 sensor. But it could also be your gas cap is not sealing properly evaportion system is not working. The only way to really know is to find someone with a code reader. If you read the Haynes manual for these vehicles they say that a non-sealing gas cap is one of the most common reason for the check engine soon light to come on.

[CD Smalley]

How do I read my computer codes? NOTE - This is a work in progress!!!!!

Tools needed:
Your car keys
A paper clip or a three(3) inch long piece of safety wire.

First thing you need to do is find your Assembly Line Diagnostic Link or ALDL. It s small black plastic piece about two (2) inches wide by one half(0.5) inch tall. It has twelve (12) female connector inside. The ALDL can be found under the driver's side of the dash, usually attached with two (2) screws to the bottom side of the dash.

The ALDL :

Now that you've found the ALDL, bend the paper clip or the piece of wire into a U shape. With the ignition in the OFF position. Insert one end into the A slot and one into the B slot. Now turn the the ignition to the ON position. DO NOT start the car. As the ECM begins it's self-test if will begin to flash the SES light to provide the codes. The flashes will appear like this : *flash* short pause *flash* *flash* long pause then repeat. Each code will be displayed three(3) times. Code 12 will be repeated to indicate the end of the set codes. If you all you get is Code 12 then you have no codes set in your ECM.

An example of a sequence for a common code :
*flash* short pause *flash* *flash* long pause = Code 12, Testing the ECM
*flash* short pause *flash* *flash* long pause = Code 12, Testing the ECM
*flash* short pause *flash* *flash* long pause = Code 12, Testing the ECM
*flash* *flash* *flash* short pause *flash* *flash* long pause = Code 32, EGR
*flash* *flash* *flash* short pause *flash* *flash* long pause = Code 32, EGR
*flash* *flash* *flash* short pause *flash* *flash* long pause = Code 32, EGR
*flash* short pause *flash* *flash* long pause = Code 12, Testing the ECM
*flash* short pause *flash* *flash* long pause = Code 12, Testing the ECM
*flash* short pause *flash* *flash* long pause = Code 12, Testing the ECM
Clearing the codes is really quite easy. Unhook your battery for about 2-3 minutes and then hook it back up.

These codes cover the OBD-I computers only.....
All currently listed codes are from the 1989 B-car Service Manual. Why? Because that's what I have. If you have others that aren't listed or need to be added, just let me know.


CODE AND CIRCUIT POSSIBLE CAUSE

CODE 12 = System check
Indicates that the ECM is functioning.

CODE 12 = No Engine Speed Reference - VIN 'Y' CARB
Indicates an open or ground in the distributor reference circuit.

CODE 13 = OPEN Oxygen Sensor (O2)
Indicates that the oxygen sensor circuit circuit or sensor was open for one minute while off idle.

CODE 14 = Coolant Sensor (CTS)
Sets if the sensor or signal line are grounded for 3 seconds. HIGH Temperature indication.

CODE 15 = Coolant Sensor (CTS)
Sets if the sensor wires or connections are open for 3 seconds. LOW Temperature indication.

CODE 21 = Throttle Position Sensor (TPS)
TPS voltage of more than 2.5 volts for 3 seconds at an engine speed less than 1200 rpm. HIGH Voltage Signal.

CODE 22 = Throttle Position Sensor (TPS)
A shorted to ground or open signal circuit will set code in 3 seconds. LOW Voltage Signal.

CODE 23 = Manifold Air Temperature Sensor (MAT)
Sets if the sensor wires or connections are open for 3 seconds or Intake Air Temperature (IAT) LOW Temperature indication.

CODE 24 = Vehicle Speed Sensor (VSS)
No vehicle speed present during road/load deceleration. NO Vehicle Speed Indication.

CODE 25 = Manifold Air Temperature Sensor (MAT)
Sets if the sensor or signal line are grounded for 3 seconds. Or Intake Air Temperature (IAT)
HIGH Temperature indication.

CODE 32 = Exhaust Gas Recirculation (EGR)
OR Vacuum switch shorted to ground on start up. Switch not closed after the ECM has commanded EGR for a specified period of time OR EGR solenoid circuit open for a specified period of time.

CODE 33 = Manifold Absolute Pressure (MAP)
MAP sensor output too high for 5 seconds or an open circuit. LOW Vacuum.

CODE 34 = Manifold Absolute Pressure (MAP)
Low or no output from sensor with engine running. HIGH Vacuum.
CODE 35 = Idle Air Control (IAC)
IAC error.

CODE 42 = Electronic Spark Timing (EST)
ECM has seen an open or grounded EST or Bypass circuit.

CODE 43 = Electronic Spark Control (ESC)
Signal to the ECM has remained low for too long or the system has failed a functional check.

CODE 44 = LEAN Exhaust Indication
If voltage to oxygen sensor remains BELOW .2v for more than 20 seconds code is set.

CODE 45 = RICH Exhaust Indication
If voltage to oxygen sensor remains ABOVE .7v for more than 1 minute code is set.

CODE 51 = PROM - Faulty MEM-CAL or ECM.

CODE 52 = Faulty or missing CAL-PACK.

CODE 53 = System overvoltage
Indication of a faulty alternator or regulator. Camaro/Firebird uses a Code 53 for Vehicle Anti-Theft System (VATS).

CODE 54 = Low Voltage To Fuel Pump
Sets when the fuel pump voltage is less than 2 volts when reference pulses are being received.

CODE 55 = Faulty ECM

My guess for your van is a code 32, the example shown, and EGR circuit failure. Quite common, cheap and easy fix.

[LTJGWorth]

Well, i've got a new problem. The van started to not idle right last night. It would start, and run for a little bit, but it would pulse and then eventually shut off. It would stay running as long as I had my foot on the gas. I needed the van this morning, and I drove it all the way to the end of my road (a little over a mile) until I got to a stop sign, and it shut off. I put it in park, started it up, put it in drive and hit the gas to go and it stalled. Couldn't get it to go. I managed to get it turned around and pumped the gas over and over and over again to get it home. Sounds to me like a fuel pump. Could it be something a little less complicated and easier to fix?

[LTJGWorth]

Ok, I've got the van to idle. I thought it may be the EGR valve. I took it off, it was closed, but I cleaned it anyway. That was after I got it to idle. It still idles, but as soon as I put it into gear, whether it be reverse or drive, it won't idle. I have to pump the gas to get it to go. It doesn't sound like it's missing or anything, what could be the problem?

[LTJGWorth]

Oh, and I got the check engine light code. It is a code 24 (Vehicle Speed Sensor). I already knew that it didn't work, because my speedometer doesn't work and it doesn't work because when I changed the transmission, the one I replaced the old one with had a gear driven VSS and mine uses the electric VSS and I didn't get shaft changed.

[CD Smalley]

Other last descriptions sound like a fuel pressure problem to me... Is this a VIN Z or W engine?

[LTJGWorth]

I was also thinking about fuel pressure, but wouldn't I notice the same problem while parked? I mean, I can rev the engine as high as it will go as long as it's in park or neutral, but as soon as it gets into gear, it stalls. My Dodge's (avatar) fuel pump went bad and it would barely idle (in park or in gear) and it had no power. Oh, and it's a Z engine.

[LTJGWorth]

Oh, and I can't hear the fuel pump buzzing when I turn the key on. The van starts everytime (sometimes with a little more cranking then others), but I can't hear the fuel pump buzzing.

[J-Ri]

Sounds like it could be a vacuum leak. That would cause the starting and idling problems, and if it made it run lean enough, the O2 sensor would read lean, illuminating the engine light.

[J-Ri]

And about the fuel pump, could you hear it in the past?

[LTJGWorth]

I don't remember hearing it in the past. The other day, i took all the air-cleaner stuff off of it to check the injectors. They are spraying the same, and it seems to be running a bit better. I did notice a vacuume line that when I put my finger over, the van ran a lot better, but when I plugged it up and tried to drive it, the damned thing sparked really big (i had the inside engine cover off) and quit on me. It started right back up but I thought there was going to be a fire. As for a check engine light, it's not showing any codes.