'81 vette throwing codes (or not)
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Joined: Aug 2011
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From: Deep River, CT
'81 vette throwing codes (or not)
Hi all, new the forum and I'm having trouble with my 'vette.
I don't drive her as much as I should. I drive her a few miles every couple of weeks. Upon starting her up a few days ago, the check engine light flashed on 2 or 3 times, then went out. I took her for a short drive, and it stayed off.
I pulled the codes, and it was code 12, code 21 (TPS), and code 23 (mixture control solenoid). I cleared the codes, and the check engine light came on again just like before. This time, ONLY code 21 flashed.
I took out the battery, unhooked the ECM, and shot some contact cleaner in the harness. Put her all back together, and no codes, HOWEVER, I can't even get a code 12 now when I jump the ALDL terminals.
So, bad ECM? She idles fine. I haven't taken her out on the road since I did all this. What would happen if the ECM was bad? Would it still run okay? Limp mode? I appreciate all suggestions, thanks.
I don't drive her as much as I should. I drive her a few miles every couple of weeks. Upon starting her up a few days ago, the check engine light flashed on 2 or 3 times, then went out. I took her for a short drive, and it stayed off.
I pulled the codes, and it was code 12, code 21 (TPS), and code 23 (mixture control solenoid). I cleared the codes, and the check engine light came on again just like before. This time, ONLY code 21 flashed.
I took out the battery, unhooked the ECM, and shot some contact cleaner in the harness. Put her all back together, and no codes, HOWEVER, I can't even get a code 12 now when I jump the ALDL terminals.
So, bad ECM? She idles fine. I haven't taken her out on the road since I did all this. What would happen if the ECM was bad? Would it still run okay? Limp mode? I appreciate all suggestions, thanks.
Last edited by 22229stingray81; Aug 25, 2011 at 01:30 AM.
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Joined: Aug 2011
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From: Deep River, CT
Just got back from a nice drive.... she rides and runs fine! The tranny locks up and unlocks (just like it always has), so we know the computer is doing something. I jumped the ALDL again when I got home and still no code 12. The lamp is working as it illuminates at startup (as normal). What the heck is going on here?
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From: Scottsdale Arizona
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Joined: Aug 2011
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From: Deep River, CT
I do have a service manual, but I'm scratching my head looking at it. I know some basic electronics, but this thing can be pretty non-descript at times. "Ground pin five on ECM terminal." My instincts tell me that the terminals on the harness attaching to the ECM are somehow numbered. I don't know how a human being could get in such a small space to see these numbers.... but I digress.
Dig this: I just jumped the ALDL again, and NOW I'm getting a code 12. How weird..... One of the locks on the upper plug of the ECM has been broken off. Perhaps it's not making great contact? I wiggled it around before I got the code 12 back, so that's what I'm going with right now. Still, it doesn't account for why no code 12 and ONLY a code 21 before I messed with anything. I've had this car for 12 years and this is the first bug like this it's had. I'm going to file this all under "if it ain't broke, don't fix it."
Dig this: I just jumped the ALDL again, and NOW I'm getting a code 12. How weird..... One of the locks on the upper plug of the ECM has been broken off. Perhaps it's not making great contact? I wiggled it around before I got the code 12 back, so that's what I'm going with right now. Still, it doesn't account for why no code 12 and ONLY a code 21 before I messed with anything. I've had this car for 12 years and this is the first bug like this it's had. I'm going to file this all under "if it ain't broke, don't fix it."
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From: Crossville TN
I suspect that tarnished connector contacts is your problem. Remove all of the connectors associated with ECM operation; clean them with Q-Tips and cleaner or very soft wire brush; wipe any residue off with a clean cloth (microfiber works well); put some dielectric grease (just a light smear) on the contacts and hook it back up. That should solve your problem AND keep that problem from recurring for several years.
P.S. Don't forget to remove and clean all ground pigtails, too.
P.S. Don't forget to remove and clean all ground pigtails, too.
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From: Deep River, CT
Thanks. I sprayed the connectors with some really good contact cleaner. Not Deox-it (I've read it has a lubricating ingredient in it, which never dries), but didn't touch the terminals on the ECM. It just connects directly to the circuit board, which I didn't want to touch. If any problems return, I'll certainly clean it up further, but I suspect the broken connector probably has a little something to do with it. It just won't fully "lock" into place without it.
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From: Scottsdale Arizona
You might get some real benefit from replacing the ECM harness. I know when I did mine the wires and connectors all but fell appart. After I did it, a lot of odd gremlins went away.
Burning Brakes
Joined: Aug 2006
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From: Eastern North Carolina
Sounds like the bad connector was your problem, if you decide to clean the connectors attched to your ECM make sure to disconnect the battery first before unpluging the ECM. You probably already knew this...Tim