Ghost in the machine!
Thread Starter
Melting Slicks
Joined: Mar 2003
Posts: 2,898
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From: Oklahoma City Oklahoma
Ghost in the machine!
The Check Engine light on my 91 comes on ocassionally for a few seconds. I doesn't do it all the time, and when it does do it, it only stays on for about 15-30 seconds. It has no codes recorded.
I was always under the assumption that the check engine light was pretty much emissions related, but a mechanic at a local shop said that the check engine light was conected to a BUNCH of stuff in the later cars, so it's anybody's guess. He told me not to worry about it.
It IS kind of frustrating though.....any educated guesses out there?
Thanks!
Larry
I was always under the assumption that the check engine light was pretty much emissions related, but a mechanic at a local shop said that the check engine light was conected to a BUNCH of stuff in the later cars, so it's anybody's guess. He told me not to worry about it.
It IS kind of frustrating though.....any educated guesses out there?
Thanks!
Larry
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Joined: Sep 2002
Posts: 95
Likes: 1
From: Leominster MA
I have a '92 LT1, so the computer and just about all the electronics are different, but...
What tips me off is how no codes are recorded. Now on my car, as I'm sure is with your car (atleast about the power interrupt), the EBCM, CCM, and ASR/ABS computers (1,4, and 9 on the on-board diagnostic for LT1's) store codes until power is interrupted (no battery) for at least 20 seconds. That was also true for my '88 L98 GTA. I lost a computer in my GTA and I remember that I used to get Service Engine Soon lights on occasion for minute intervals with no stored codes. It then died in my driveway and wouldn't start. A ride to the junk yard, $45 for an ECM, an hour later she ran just perfect.
My LT1 used to do the exact same thing too. Usually on colder mornings, once every year or so, the light would illuminate for about 20 seconds and go out. My car threw a code however, (I'm guessing at the number) 36, which was a faulty EGR valve connection or EGR vacuum leak.
I just had a thought...when you say "no codes" did you even get a code 12? If you didn't, then the diagnositic module can not talk to the ECM and you have a computer system problem. If you get a code 12, then it still might be the ECM.
If you are getting check engine lights, but no codes are recorded, I might suspect ECM failure. I remember, in the HELMS manual, they discuss that faulty "code throws" demonstrated by no stored codes and intermittent Service Engine Soon lights describe a malfunctioning ECM. I have even heard of cases of a grounded or short-out ECM that loses power after you turn off the car (which will erase all codes). Check for constant power to the ECM while the car is off as a quick test.
Besides the code 12, which just states that the ECM is there and the diagnostic system can talk to the ECM, there is no code for a faulty/malfunctioning ECM, since ECM doesn't "know" if it's malfunctioning. Hence, why you might not be getting a code. In all honesty, I wouldn't follow the mechanic's advice. The light doesn't illuminate because it feels like it, but because there is a problem; either with the sensors the ECM is connected or the ECM. I would try to atleast find out the problem before the car leaves you on the side of the road or in a parking lot. Pick up a HELMS and try to diagnose a faulty ECM.
Take Care!
What tips me off is how no codes are recorded. Now on my car, as I'm sure is with your car (atleast about the power interrupt), the EBCM, CCM, and ASR/ABS computers (1,4, and 9 on the on-board diagnostic for LT1's) store codes until power is interrupted (no battery) for at least 20 seconds. That was also true for my '88 L98 GTA. I lost a computer in my GTA and I remember that I used to get Service Engine Soon lights on occasion for minute intervals with no stored codes. It then died in my driveway and wouldn't start. A ride to the junk yard, $45 for an ECM, an hour later she ran just perfect.
My LT1 used to do the exact same thing too. Usually on colder mornings, once every year or so, the light would illuminate for about 20 seconds and go out. My car threw a code however, (I'm guessing at the number) 36, which was a faulty EGR valve connection or EGR vacuum leak.
I just had a thought...when you say "no codes" did you even get a code 12? If you didn't, then the diagnositic module can not talk to the ECM and you have a computer system problem. If you get a code 12, then it still might be the ECM.
If you are getting check engine lights, but no codes are recorded, I might suspect ECM failure. I remember, in the HELMS manual, they discuss that faulty "code throws" demonstrated by no stored codes and intermittent Service Engine Soon lights describe a malfunctioning ECM. I have even heard of cases of a grounded or short-out ECM that loses power after you turn off the car (which will erase all codes). Check for constant power to the ECM while the car is off as a quick test.
Besides the code 12, which just states that the ECM is there and the diagnostic system can talk to the ECM, there is no code for a faulty/malfunctioning ECM, since ECM doesn't "know" if it's malfunctioning. Hence, why you might not be getting a code. In all honesty, I wouldn't follow the mechanic's advice. The light doesn't illuminate because it feels like it, but because there is a problem; either with the sensors the ECM is connected or the ECM. I would try to atleast find out the problem before the car leaves you on the side of the road or in a parking lot. Pick up a HELMS and try to diagnose a faulty ECM.
Take Care!
