1991 Chevy Camaro Code 42 SES Light

1991 CHEVROLET CAMARO
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EGILLIAM
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1991 Camaro 3.1 289000 miles, NO OTHER PROBLEMS. Just about 2 months ageo I started my car and the service engine soon light came on. Right before that it started idleing rough but not terrible bad (I had to look at my tach to see it bouncing). Also my tach reads way off, I mean when it idles it idles at 2500 rpm and when I am driving it is on the peg (this was happening at leasts 2 years before the service engine soon). Any way the light comes on as soon as I turn the car on. If I unplug the Ingition Control module which I just replaced, the light will not come on till I am about half a mile down the road. I have replaced like I said the ICM as well as the ECM. Any Suggestions or questions?
Mar 20, 2007 at 12:56 PM
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I would start by finding what codes are in it, clearing them, and driving until it comes back on, and again recording the codes.
Mar 20, 2007 at 1:06 PM
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EGILLIAM
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I did try that. The code was 42 and it came back within 2 secs. I was thinking it might be the IAC but wanted someone elses opinion before I spent 100$ on a tiny device.
Mar 20, 2007 at 1:09 PM
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EGILLIAM
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I know that my car has lots of miles on the orignal engine but, it does not leak any thing, has no missing, and no knocking. When I start the car up before I pull out it turns the service engine soon light on. Now when it warms up I can mash the throttle and it will run slow until the Tach goes out of the mesurable range then it starts running fine. Just ask I have plenny of info on this stupid thing.
Mar 20, 2007 at 1:26 PM
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SERVICE WRITER
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Iac should be a code 35 I think.

42 "may" end up being a computer
Mar 20, 2007 at 1:31 PM
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EGILLIAM
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Thats what I thought to. So I went and replaced it as well. Still did not help. It did fix all the other problems I was having thou.
Mar 20, 2007 at 1:33 PM
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SERVICE WRITER
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Since there are no performance problems, I doubt a wiring short or open. ignition control module would be the next most probable cause.
Mar 21, 2007 at 11:13 AM
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EGILLIAM
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I tried that to it did not help. Any more possibilities
Mar 21, 2007 at 11:27 AM
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SERVICE WRITER
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Only thing left is wiring, as I understand it. Open or short. Run through the wiring according to the info you have, or I can send what I have.
Mar 21, 2007 at 11:42 AM
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EGILLIAM
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OK that is what I was thinking I have a Chilton’s Manuel. It shows the wiring out line I will try that and see what happens thanks aLOT.
Mar 21, 2007 at 12:04 PM
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SERVICE WRITER
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I came accross a little more explanatory info if you need it.
Mar 22, 2007 at 10:50 AM
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EGILLIAM
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Yeah if you don't mind I kind of figured mine cannot be the only one in the world that had this probelm
Mar 22, 2007 at 10:57 AM
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SERVICE WRITER
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on its way
Mar 22, 2007 at 11:13 AM
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EGILLIAM
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Sir, Thank you for all your help I have just one more question, The wires that run from the ECU to under the hood do they go under the front right quarter panel??
Mar 27, 2007 at 2:42 PM
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SERVICE WRITER
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Sir?

I really don't know, may have to undo some harnesses to see what colors run through it.
Mar 27, 2007 at 3:06 PM
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EGILLIAM
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Thanks Paul for all your help.
Mar 28, 2007 at 10:34 AM
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SERVICE WRITER
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My pleasure.
Mar 28, 2007 at 1:34 PM
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EGILLIAM
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Here was the problem My car had the check engine soon light and gave the code 42. Well after extensive research I found that Code 42 for a camaro is the ckt between Computer and Distributer, Including the COIL and Wires. Well I replaced everything that was in the path except for the wires from ECM to distributor. That was the next step. So we started testing the cables with the Chiltons Manuel for a camaro. After testing the results stated the Ingition Module was bad so we had it tested at auto zone and it was clear. So we said the only thing left is the wires. Before we replace the wires we notice that the tests were reading very high resistance when the 4 prong connector was connected to the ICM. So we cleaned and made the connectors tighter and it fixed all the problems. Thanks for all your help
Jun 12, 2007 at 10:11 AM
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SERVICE WRITER
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It can be frustrating when test data shows a part that is bad, only to find out otherwise. A shop begins to look "shady" or "is guessing" when this happens.

Glad to hear you got it solved.
Jun 12, 2007 at 10:43 AM

Suggested Repair

For code 42 with the service engine soon light, check the circuit between the ECM and distributor, including the coil, ignition control module, and wiring. In this case the ICM tested good, but the four-prong ICM connector showed very high resistance; cleaning and tightening the connector terminals fixed the light and related symptoms.

Conversation Summary

A 1991 Chevrolet Camaro 3.1 with high mileage had a service engine soon light that came on immediately, code 42 that returned quickly, rough idle, and a long-standing inaccurate tach. The owner had already replaced the ignition control module and ECM. The expert advised retrieving and clearing codes, noted code 42 is not an IAC code, and pointed next to the ICM and then an open or short in the wiring. Using a Chilton manual, the owner found high resistance only when the four-prong connector was attached to the ICM. Cleaning and tightening those connectors resolved the problems.

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