Service Engine soon light question.
Thread Starter
Pro
Joined: Mar 2005
Posts: 722
Likes: 70
From: Fla
Service Engine soon light question.
I have a 1993 Vert Lt-1 that has 50k and while I was driving the (Service Engine Soon) light came on after about one hour of driving. The car has had a recent oil change and runs great. no overheating or knocking or anything. When I turn the car off and turn it on the light turns off and stays off. I am new to the c4's what can this be? maybe a sensor fouling? Any info will be appreciated. Thanks, ed ramos
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
Service Soon light...
Clay is right about reading the codes. But, depending on what is setting it off - especially if the problem is dynamic - it might be better to have a scanner or a laptop w/ the appropriate s/w monitor it in order to "see" what is going on. A static code is not always set, unless the problem persists.
Case in point: Similar symptoms - see if this sounds like your problem:
I had an O2 sensor go bad, and the computer defaulted to a 488 mV setting on that sensor. Anytime the working sensor was out of the 488 "default window", the Sevice Soon light would come on ('95 LT1), the system would switch to open loop, and the scanner (in monitoring mode on the seat next to me) would display/record both events. While in open loop, the engine would run rough in different load conditions, and my instant gas mileage readout would drop 5-6 mpg. However, after shutting the engine off and then switching the ignition on to read the codes, none would be set. Firing it up again, and in a few seconds (engine still hot) the system would switch to closed loop.
Replacing the offending O2 solved the problem. I hope your problem is as simple as mine was.
P.
Case in point: Similar symptoms - see if this sounds like your problem:
I had an O2 sensor go bad, and the computer defaulted to a 488 mV setting on that sensor. Anytime the working sensor was out of the 488 "default window", the Sevice Soon light would come on ('95 LT1), the system would switch to open loop, and the scanner (in monitoring mode on the seat next to me) would display/record both events. While in open loop, the engine would run rough in different load conditions, and my instant gas mileage readout would drop 5-6 mpg. However, after shutting the engine off and then switching the ignition on to read the codes, none would be set. Firing it up again, and in a few seconds (engine still hot) the system would switch to closed loop.
Replacing the offending O2 solved the problem. I hope your problem is as simple as mine was.
P.
Le Mans Master
Joined: Jul 2002
Posts: 5,818
Likes: 2
From: Alive and well in Burlington NC
Find the codes
You can use a paper clip to short openings A and G (see below) on your ALDL (under the DS knee pad). Turn the ignition to the 'run" position and your speedo will tell you what codes are stored.
