Help! Check Engine Light 1991 C2500 Pickup

[BlownChevelle]

I have a 1991 C2500 pickup that insists on throwing a check engine light on a regular basis.

Its the 5.7L V8, the idle seems higher when it comes on, the light only stays on while at idle,

but if you give it throttle it goes out? Plus its OBD1 so i have cant get the code. Please help!

[bossier62guy]

I have a 1991 C2500 pickup that insists on throwing a check engine light on a regular basis.

Its the 5.7L V8, the idle seems higher when it comes on, the light only stays on while at idle,

but if you give it throttle it goes out? Plus its OBD1 so i have cant get the code. Please help!

 

Try this:

http://www.freeautomechanic.com/diagnostictroblecodes5.html

[thecraft]

More info here:

 

http://www.troublecodes.net/GM/

http://tvoffer.tripod.com/gmcodes.htm

[BlownChevelle]

Thanks so much guys, so here is what it gave me:

 

 

CODE 22

 

 

 

Trouble Code 22 indicates that the Throttle Position Sensor (TPS) is reading abnormally low. TPS volts should be close to 0.42 V at closed throttle and rise smoothly in about 0.02 volt increments to a maximum reading of about 4.85 volts at WOT.

 

 

 

The conditions for setting this code are:

 

 

 

• the engine is running, and
  
• TPS reading is < 0.20 volts
  

 

 

Note: During a Code 22 condition, the ECM uses a default TPS value of 2.6 volts. This will cause the engine to idle very high.

 

 

 

Typical causes for this code include:

 

 

 

1) Maladjusted TPS

2) Defective TPS

3) No +5 volt reference to TPS

4) TPS-return to ECM is shorted to ground or to sensor ground

5) Defective ECM

 

 

 

NOTE: The TPS must be adjusted to about 0.42 volts at closed throttle for the ECM to auto-zero properly. If necessary, adjust the TPS to bring the voltage up or down to this value at closed throttle.

 

 

 

 

 

 

 

 

 

 

 

*** So here is my big question, i replaced this TPS a year ago or so, could it have gone bad again so soon or am I missing something? Anyway to tell if its a defective ECM? How can you adjust a TPS?

 

 

[bossier62guy]

Thanks so much guys, so here is what it gave me:

 

 

<a href="

http://" target="_blank"></a>CODE 22

 

 

 

Trouble Code 22 indicates that the Throttle Position Sensor (TPS) is reading abnormally low. TPS volts should be close to 0.42 V at closed throttle and rise smoothly in about 0.02 volt increments to a maximum reading of about 4.85 volts at WOT.

 

 

 

The conditions for setting this code are:

 

 

 

• the engine is running, and

   

• TPS reading is < 0.20 volts

   

 

 

 

Note: During a Code 22 condition, the ECM uses a default TPS value of 2.6 volts. This will cause the engine to idle very high.

 

 

 

 

 

Typical causes for this code include:

 

 

 

1) Maladjusted TPS

 

2) Defective TPS

 

3) No +5 volt reference to TPS

 

4) TPS-return to ECM is shorted to ground or to sensor ground

 

5) Defective ECM

 

 

 

NOTE: The TPS must be adjusted to about 0.42 volts at closed throttle for the ECM to auto-zero properly. If necessary, adjust the TPS to bring the voltage up or down to this value at closed throttle.

 

 

 

 

 

 

 

 

 

 

 

*** So here is my big question, i replaced this TPS a year ago or so, could it have gone bad again so soon or am I missing something? Anyway to tell if its a defective ECM? How can you adjust a TPS?

 

 

 

Sure that part could have gone bad already, hell it was probably made in China. Back probe the connector using a digital multimeter to check for the proper voltages and smooth operation of the TPS. I don't have a clue which wire it is on your truck though, maybe someone that has a manual that covers your model year can check that out for you.