Service Engine Soon Light
Thread Starter
Heel & Toe
Joined: Sep 2012
Posts: 24
Likes: 1
From: West Rutland Vermont
Service Engine Soon Light
1986 C4 my service engine soon light comes on after I have been driving for about a 1/2 hr and will go out after another 1/2 hr. I have not noticed any change in performance, If I stop and shut the engine off it will go out but again it will come on. Can you run a scan test if the light has gone out or does it have to be on to test. Has anyone experienced this intermittent condition. Stock engine no modifications.
Safety Car
Joined: Jan 2004
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http://www.corvettephotographs.com/c4vettes/codes.htm
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I'll bet you get an error code 32 -- EGR.
It means that the EGR system is not working. When the ECM commands EGR, it turns on the EGR solenoid, which applies vacuum to the EGR valve. When the EGR valve opens, hot exhaust gases flow through the EGR tube that goes over the top of the passenger side valve cover. In that tube is the EGR thermo switch, which closes when it gets hot from the exhaust gases flowing through the EGR tube. If the ECM does NOT see that switch closure it sets error code 32. The complete series of events has to happen to make the thermo switch close, so you need to check all the links in the chain.
