IrishJoker

In Maryland you are required to get an emissions test every two years. So I did the 95 this past Saturday, she passed the test with flying colors. On sunday I decided to take a cruise. Drove about 100 miles along the upper Chesapeake. On the way home I notice the "Service Engine Soon" light had come on. I do have a scanner for the OBD I/II. Havent' had time to run the codes. But what is the most common cause of this fault condition? According to the owner's manual it should only come on and stay on if a fault is detected. The car IS NOT running rough at all - like when an oxygen sensor went out and I had an over Rich condition - computer was actually dumping more fuel then required because of the lack of the feedback from the sensor I guess.

NEVRL8T

There are a whole multitude of things that could cause an SES light. Thats the basic "warning" that there is a problem somewhere - just about anywhere.

IrishJoker

I suppose but, the basic impression I get from the owner's manual is that is mainly deals with the fuel system and the emissions system.

jrp

Those, plus all of the other engine controls. There are many, as mentioned above, and description/diagnosis of all the codes fills up half of Vol. 2 of the service manual.

The items in the owner's manual (I haven't looked in a long time) are likely just the things that can be easily corrected by the owner before deciding to take the car in for service. Tightening the fuel filler cap comes to mind.

GKK

Same thing just happend to my "91".

My Vette passed a California emmisions test with flying colors but, six months earlier the SES light lit up. It would only light up occassionally about once a week and then it started to come on once every night on the way home from work.

The trouble code was a #32 (EGR system).
The engine ran fine and if I shut the ignition off and restarted, the SES light would go out. I checked the EGR valve and EGR solenoid vacuum and everything was fine also, the "91" Vette doesn't use an EGR temperature switch like previous C4's.

After reading here on the forum, I found that the ECM could be bad so, I ordered a rebuilt ECM from Ecklers for $114 and so, far no more SES light!

CFI-EFI

The "Service Engine Soon" light" means to service the engine soon. The first step in servicing the engine is to check for codes to see what system(s) caused the light to come on. A code from a system doesn't necessarily mean that the titled item in that system is bad. A code for the EGR valve doesn't mean the EGR valve is bad. It means out of parameter info was sent to the computer from the EGR system. The EGR valve MAY be bad, but the fault may not even be in the EGR system, let alone the valve. One must, second, after determining what codes are present, trouble shoot for each code to find the true cause. To ask, "But what is the most common cause of this fault condition?", when the only known "fault condition" is the fact that the SES light came on, only perpetuates and encourages throwing money at a yet to be determined problem. Pull the codes and properly trouble shoot them.

RACE ON!!!

IrishJoker

Got a code 32 back from Actron Scanner - EGR valve. So I'll check all the connections form the EGR to the ECM and all the vacuum lines, then reset the Service Engine Soon light and see what happens.