Service Engine Soon Light Ghost!
 

My 95 2-door Yukon has a SES light Ghost! Here is the scenario...

-Start truck
-Drive Truck
-After 1-3 minutes the SES light will come one for less than 30 seconds
-Truck is ODB 1 and will not store a code!
-tried driving with scanner hooked up
-scanner shows no codes are stored EVEN WITH SES LIGHT ON!!!!!

This happens 4 out of 5 times... it is not constant.

Any Ideas?
This may be a key to the ol' girl passing California Smog!

Re: Service Engine Soon Light Ghost!
 

o2 sensors will do that garbage. check there good.

Re: Service Engine Soon Light Ghost!
 

follow what ever advice that chevy tech gives you.....

hopefully he will see the thread and chime in.... if not, send him a PM

Re: Service Engine Soon Light Ghost!
 

Tommie – thank you for your vote of confidence.

jbclassis - Does the scanner show the system ever making it to closed loop operation?

The computer could have failed and the system is running off the back-up in the PROM (MEM-CAL)

As a test you could unplug the TPS and see if the computer is able to set a trouble code when there is a problem.

Re: Service Engine Soon Light Ghost!
 

I am going to replace the O2 anyway... I don't have a code for lean or rich, but I have not replaced it since I bought it in 05.

Thanks, I will definitely listen to him

ChevyTech, The scanner I have is fairly generic. It recognizes the system as a GM OBD 1, asks for year, 8th digit, truck or car, and trans. Then it gives "memory retrieval successful..." Then "There are no stored codes in the computer"

I unplugged the Computer controlled advance wire and it set the SES light, I unplugged the EGR solenoid and it set the light... is this what you are looking for, or does it specifically have to be the TPS?

Re: Service Engine Soon Light Ghost!
 

Don't trust what the tool tells you.
Read the codes manually.

Checking OBD1 computer codes without a scan tool.
http://67-72chevytrucks.com/vboard/s...5&postcount=11


Those are good enough tests. No need to try unplugging the TPS. The computer is seeing what is happening and my guess is that there are trouble codes set, but the tool you are using can read the codes.

Lets us know what codes you find.

Re: Service Engine Soon Light Ghost!
 

And the lucky number is...

...13

O2 sensor circuit failed

First thing I will be doing is replacing the o2 sensor then we will go from there.

Re: Service Engine Soon Light Ghost!
 

My '92 does something similar, but I haven't checked the codes yet.

Start the truck, it runs like a top, after about 15 minutes of driving, the SES comes on and will sometimes stay on, sometimes go off. The truck doesn't seem to run any different and if I stop for even a minute, the light will reset and come back on later, maybe.

Sounds like it might be something like o2 or EGR type sensor, I will run the codes when I get home.

Re: Service Engine Soon Light Ghost!
 

Check the "Testing the O2 sensor" videos on you tube. You can test the O2 sensor on the car with a digital voltmeter and a wire probe.

Re: Service Engine Soon Light Ghost!
 

I am waiting for another TBI for my '88 5.7..... The shaft is a tad loose causing a vacuum leak. The engine runs a bit rich due to the leak, and a slight rise in RPM causing the SES to turn on / off. The leak has been there for a while, but I didn't notice, because the rise was slight and I got used to the idle, not realizing the RPM change.

No codes.

Re: Service Engine Soon Light Ghost!
 

Vac leak maybe? That truck was designed to run on gas, at the pump you get anything but that. Carbon deposits make it worse. Maybe some non ethanol gas for a tank or so and steam out the carbon with water(better than seafoam) and possibly se if symptoms change? Wouldnt really cost anything and worth a try?