PCM? problems...
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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PCM? problems...
I'm new here (just registered), so go easy on me. I picked up a 93 corvette a couple months ago for a car lot, and now getting codes. It's the LT1. I got in the car today, just like everyday, to go for a drive. I noticed there was a check engine light on, but was in a hurry
. After the car started to buck occasionally, I turned around and parked it. I noticed the check engine light was on, the service ASR light too. The sys and security lights flashed 3 times in sync. My speedometer wouldn't pick up my speed either, it just said 0.
I pulled several codes.
1. C41 H41 H72 H74
4. ERR
9. H72
I'm kinda thinking that maybe there is something loose, but I am not sure. The other thing I have noticed while under the dash was a toggle switch someone mounted. It goes to the mounting bolt to the pcm, to some relays next to the fans. Not sure what this is supposed to do, but I would like to remove this soon if it is not needed.
Ill look tomorrow for something loose at the pcm, but other than that, I am not sure. Any help would be great.
. After the car started to buck occasionally, I turned around and parked it. I noticed the check engine light was on, the service ASR light too. The sys and security lights flashed 3 times in sync. My speedometer wouldn't pick up my speed either, it just said 0.I pulled several codes.
1. C41 H41 H72 H74
4. ERR
9. H72
I'm kinda thinking that maybe there is something loose, but I am not sure. The other thing I have noticed while under the dash was a toggle switch someone mounted. It goes to the mounting bolt to the pcm, to some relays next to the fans. Not sure what this is supposed to do, but I would like to remove this soon if it is not needed.
Ill look tomorrow for something loose at the pcm, but other than that, I am not sure. Any help would be great.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
See if this helps:
http://chevythunder.com/199295_lt1_trouble_codes.htm
Also, is the toggle part of the code 41 issue?
http://chevythunder.com/199295_lt1_trouble_codes.htm
Also, is the toggle part of the code 41 issue?
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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So I checked it again today. So the codes were 1. C41 H41 H72 H74 4. Err 9. H72
So 1. C41 is ECM data communications lost. H41...same... H72 LCD dimming open H74 LED display open 4. Err.... can't communicate with mod? 9. H72 serial data link error.
I would seriously think something came unplugged, I just don't know where to look. I tried pushing on the ECM plugs (4 of them ), but that had no effect.
Any idea on where the "ECM data communications" is? Or even the "serial data link" ?
So 1. C41 is ECM data communications lost. H41...same... H72 LCD dimming open H74 LED display open 4. Err.... can't communicate with mod? 9. H72 serial data link error.
I would seriously think something came unplugged, I just don't know where to look. I tried pushing on the ECM plugs (4 of them ), but that had no effect.
Any idea on where the "ECM data communications" is? Or even the "serial data link" ?
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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another thing I have noticed through multiple forums. If the ccm is bad, the car wont start. My car does start, and idles on it's own. Sometimes it is rough, but seems to smooth out. Not sure if it helps, but I have 50k on the car, so I was kinda thinking nothing needed replacing...
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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Just went out and looked again. The toggle switch was grounding the green/white wire on one relay, dark blue/ light blue wire on another.
Also, I started it up and let it run a little after/while tapping on the ecm and random stuff. nothing. I noticed it was idling high (800, which I assume is for it being cold) , but than got higher (up to 1500). About 1200rpms, the car smoothed out, dropped to 500 rpms, all problem lights went out except ASR light. Car ran great for about 30 seconds, than lights came on, and went back to acting up. I noticed even from key on, to the point I shut off the car, the cooling fan was blowing as fast as it's little heart could.
Also, I started it up and let it run a little after/while tapping on the ecm and random stuff. nothing. I noticed it was idling high (800, which I assume is for it being cold) , but than got higher (up to 1500). About 1200rpms, the car smoothed out, dropped to 500 rpms, all problem lights went out except ASR light. Car ran great for about 30 seconds, than lights came on, and went back to acting up. I noticed even from key on, to the point I shut off the car, the cooling fan was blowing as fast as it's little heart could.
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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Went back out again and pulled out the wire that went to the relays that someone put in to that toggle. I unhooked the battery and let it sit for about a min. I plugged it back in, and started the car. Everything worked. Turned the car off, then back on. Everything was how it should. Fans stayed off while it was cold, unlike when the error is happening they stay on. I decided to run it down the road to see if it fixed the problem. I got about 3 blocks, the car stumbled, lights came on, sys and security lights flashed. I turned around came back and turned off the car. I tried doing the battery thing again, but as soon as I tried to start it, the lights came right back on, including the fans on high speed.
Really confused and any help would be great.
Really confused and any help would be great.
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Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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I went out and started the car. Lights and all as expected. As I went to turn it off, it sounded different. I turned it off, then back on. No lights, everything was fine. With the hood open, I flicked my finger on the ecm and lights came on and you could hear the car run rough. Trying to hunt down a loose connection, or even a loose pin in the ecu.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
It's my understanding that is a difficult ecm to come by? I have a memcal if you need one, but it sounds like something shorted in the ecm if it happens when you wiggle the plugs.
Here's a thread you might find interesting:
http://forums.corvetteforum.com/c4-t...cm-repair.html
Here's a thread you might find interesting:
http://forums.corvetteforum.com/c4-t...cm-repair.html
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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I tried wiggling the wires, but that didn't help. Normally with something like this I am arms deep in fixing my cars. Autozone has the option of me bringing mine in, they send it out and they fix it, then return it. This costs 160.00. Then, I need to take it to the dealer to reprogram it. Total cost....280.00. Way more than I wanted, seeing how I was laid off a week ago. Thank god for savings account I guess.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
The 93 has a removable memcal, so you remove it, have them fix the ecm, and put it back together. The programming is on the memcal, and GM can't reprogram it. You'd need a nut like me, or some of the other guys here to do it. 93 was the last year before flashable ecm's.
Thread Starter
Cruising
Joined: Jul 2013
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So I called today and checked on it. After 16 mins of being on hold, I finally got someone. He was kinda reluctant to give me any info, but I guess after saying my part came from auto-zone, it was enough info to know which part was mine. I kinda thought they would need more info, maybe a invoice or part number or something, but they knew which it was. He explained that they had to replace the microprocessor. He said it should be sent out Tuesday, and get to my place Wednesday. I asked if it would be more like Thursday or Friday, and he assured me Wednesday. So, we shall see.
Thread Starter
Cruising
Joined: Jul 2013
Posts: 14
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So I just wanted to update everyone that I got my computer back today. I went ahead and put my mem-cal back in and plugged everything in. It fired right up. I finished bolting down the computer, and took it down the road to see if anything bad happens. Car ran great, no lights or bad sounds. I missed my car, and that was the longest 3 weeks ever! Now it's time for a bath. 