Check Engine light

[BigDakota]

Thanks Robb.......$$$$$$$$..!!!!!

 

[Stephen S]

comes on just on long trips doesn't do it around town, just on trips when i'm doing over 65 for a long period of time

My 95 started doing this too, only after driving at highway speeds for a few hours. The CEL will come on and go off...seemed random and when I checked the codes, the system passed. The engine seemed to be running normally, with no symptoms of anything wrong. But Sunday night I was driving for a couple of hours on the interstate and the light came on and stayed on...first time it stayed on all the way home. I left it running and checked the codes:

116 - Engine coolant temperature sensor - Signal voltage is high or lower than expected

172 - Heated Exhaust Gas Oxygen sensor - Voltage signal indicates "lean" (Bank #1)

I figured the coolant was hotter because I was driving for 2 hours instead of just warming the engine for a couple of minutes like the directions say. But would a bad O2 sensor toss the second code?

 

[MrShorty]

Was the 116 a KOEO (before separator pulse) or memory code (after separator pulse) or are these KOER codes? If the engine was warmed up, it shouldn't have triggered a 116. There's potentially a problem with the ECT circuit, which could conceivably trigger faults in the computer's mixture calculation.
KOER/CM 172 indicates that the O2 sensor signal stayed low (lean) without ever showing rich. O2 sensor should swing from low to high (lean to rich) when everthing's working as it should. This could be a bad O2 sensor, it could also be a vacuum leak, bad fuel injector, or something else. NOrmally, the correct approach to diagnosing codes is to identify KOEO codes and resolve KOEO codes. Then identify and resolve any KOER codes once KOEO test passes. Then, if there are any CM codes left to worry about, resolve any CM codes.

 

[Stephen S]

Those codes were KOER codes taken after the truck was driven at highway speed for two hours. That was the first time that the CEL stayed on long enough for me to get home and run a test. It usually goes off before I get home, and the light does not come back on when the engine is restarted. Also, it does not come on at all during the shorter trips around town.

I just went outside and completed a KOEO test, a KOER test, and a cylinder balance test. All tests show system pass. No CM codes.

 

[MrShorty]

Interesting. The CEL will come on for an extended stretch, and not store a code. I would almost start by suspecting there might be a problem with the KAM power supply, computer power supply, or computer ground.
This might be a case where a scanner would be useful, so you can monitor stuff as you drive.

 

[Stephen S]

What is the KAM power supply?

I would think that if there were a problem with the computer ground or computer power supply I would be having more systemic issues than just an intermittent CEL. I'm not really sure what to do with it though. I'd hate to spend the money and replace O2 sensors that are fine. Aside from the CEL, I don't see any other symptoms of a problem. Unfortunately, I don't have recent, accurate records for my gas mileage. I suppose that lower than average gas mileage may point to a bad O2 sensor, especially if it is reading lean and my code suggests.

 

[MrShorty]

KAM=Keep Alive Memory. The computer is supposed to store a code when the cel comes on that would indicate what fault the computer saw. It's not storing a code, so something isn't right.
I suppose it could also be a short to power/ground in the CEL circuit.