AFTER ALL THE WORK BELOW, I FINALLY GAVE UP AND GOT ANOTHER CAR. WHILE THEY WERE CHANGING THE GO-FAST GOODIES OVER, THEY FOUND A BURNT WIRE UNDER A HEADER, FIXED IT AND PROBLEM SOLVED. OH WELL.

So, a couple weeks back, the car got in the habit of, once it warmed up, Service Active Handling and Service Traction Control would pop up.

Also, after the car is warm, most days but not all, the Security light comes on.

The problem got steadily worse over the course of a month. The next thing to go after the Security light would be the speedo bouncing around a little, then a few minutes later, the trans would start acting weird, locking into a lower gear. If I kept going, it would finally try to shut down the car, limp mode, or the throttle would simply quit working.

Once the car cooled off, all back to normal, no issues at all. It had gotten bad enough that I couldn't drive it more than ten minutes before it would go wacky.

Once, the speedometer suddenly started going up and down wildly, and some kind of warning popped up in the DIC. Only happened once.

One time, the water temp gauge just dropped to zero, and the DIC warned the car was overheating. It was not. Problem hasn't shown up again since.

Last night I stop at a restaurant for dinner, and the fans kept running. It not warm here yet, and usually the fans shut off just a couple seconds after the engine. I stood there a minute or so, and they just kept humming along. I went inside, came out a couple hours later, and they were still running away. Today they are fine.

Note that I also replaced the battery a couple days ago, to see if that would fix the issues, it did not. The connections look fine, at least where they hook to the battery.

All this points to some kind of communication issue in the car. Either data isn't getting to where it needs to go, or a computer somewhere in the car is screwing up what to do with it. And the problems only start once the car warms up.

Any common routing for all this information? Likely causes? I am loathe to take it to the dealer and let them start replacing everything trying to track something down. Could it be a ground or power supply somewhere? Note the car does have 97K miles on it.

Usual brilliance GREATLY appreciated. Thanks.

 

take a look at the other ends of the battery cables.
the cable on the starter the nut is known to come loose and or corroded, also the ground from the frame to the block.
you might want to unplug clean and reseat the connectors on the ECBM & ECM also

 

I will definitely look at as many connections as I can get to. I purchased some contact cleaner, so hopefully that will help as well.

 

Check these 2 blue connectors under the passenger side floor carpet above the fuse block. Make sure contacts are clean and tight. Sometimes they come loose if passengers put their feet up on that part of the carpet and mash down on the connectors.

 

Also check the ground wires. My first C6 did that and after GM bought it back, I found out that it was the ground wires causing the issues.

 

I agree, the BCM connectors under the passenger floor board are a good place to check. Also on that issue, do you happen to have a passenger in the car when things go wrong? There was a similar post years ago that turned out things only happened when a passenger was in the car with feet pushing on the floor board and causing problems with the BCM connectors.

One more to look at, the alternator. You can read through this discussion with all the symptoms but the pay off is in post 20, it was the alternator connector.

https://www.corvetteforum.com/forums...-when-hot.html

 

I agree with the above comments, these cars go whacky when the battery starts to go.

 

I will check both the alternator and the passenger floorboard box. I looked at the several of the grounds around the car, they all looked clean and happy. The starter wire looked good as well.

Thanks.

 

So, I looked at the alternator, and sure enough, I had rigged up a catch can on the driver's side long ago, and the hose going back over to the other side was laying on top of the plug that goes into the alternator on top, looking like it was pulling sideways on it. There are three TINY wires that come out of a bundle and go into that plug. The end one looked like it was completely pulled out.

I rerouted the hose, then pulled the plug and gently tugged the tiny wires. None of them came out, but I imagine that end one is likely on its last legs, probably right at breaking down where it goes into the plug. I pushed it in some, got them all nice and straight, and took the car for a drive.

It has been taking just a couple minutes, just barely starting to warm up, and off everything goes. This time, after 15 minutes of driving, a few minutes of that with oil and water at full operating temp, nada. When I was less than a minute from home, they finally went off. It's gotta be that plug.

So, I'll replace that plug, and hopefully that will be that. I will report back once it is done. I still am gonna look at the BCM box as well.

Thanks again for the usual brilliant assistance. I love this forum!

 

Great! Simple fix!

 

Reporting in.
So, it is not fixed yet. I purchased a new plug at the dealer. When I called them up to see if they had one in stock, the parts guy asked "Two wire or four wire?" Ummmmm, mine has three?

So, I purchased the four wire version, and indeed, the old plug looks identical, just doesn't have anything in that fourth slot of the plug, no wire coming in. Is there supposed to be a fourth wire??? That might be my issue.

I did go ahead and install the new plug. Just left the fourth wire on the plug wrapped and hanging. I didn't readily see anything to hook it to. Problems all still the same.

I would REALLY be curious about that fourth wire! If anyone can tell me whether there is supposed to be one. I took a REAL hard look at the one that came out, there is a red little stub down in that fourth hole, but it looks cleanly just red, like a little plug. No sign of actual wire, or a ragged tear, etc.

Thanks.

 

And, I pulled the plug and looked beneath. Three prongs down in there, so it is indeed a three wire plug. And the contacts, etc., under the plug was sparkling clean. A triple rubber seal will do that for ya.

While I was playing with it, I notice another couple of wires that came off the same bundle, and went down behind the alternator, to connect to something plugged into the engine. Very snug and warm passageway, AND, the tape wrap, just basic electrical tape, was melted through in a couple places. The wires didn't look damaged, but clearly they have had some heat. I rewrapped them, then slid a short piece of 1/2" hose over it to give it a bit of protection.

After it cools all the way down, I'll see if there is any difference.

I also saw a ground connection on the passenger side, near the front, there was a LITTLE rust on it, with lots of connectors coming together there, I suppose I will pull it and put it back.

Pluggin' along.

 

My 2007 has 3 wires.

 

So, when the car is cold and I start it up, voltmeter in the dash says 14.4. After it starts to warm up, it drops to 14.0. It then stays exactly there, even after the car warms up completely, the electronics goes nuts, the voltmeter still says 14.0, never wavers a bit.

Could it still be the alternator? I know there are supposed to be multiple diodes in the alternator, do they go to different circuits, or do they all run together?

Could the problem be the alternator?

And, how much of a hassle to pop a new one in there?

Thanks.

 

So, finally tried removing the battery connection to the back of the alternator, then just ran a jumper cable from the hot post on the battery to the post on the back of the alternator. Voila, no more problem. Fully warmed up, absolutely no issue at all. Shut it down, took off the jumper, put the pre-existing connection back, started it back up, the whole car went crazy instantly.

So, it IS that hot circuit from battery to starter to alternator. I suppose I'll let it cool off, then pull the starter, pull and clean that connection, put it back together and see if that takes care of things.

I would note, a couple years back I switched to ZR1 exhaust manifolds and cats, so I could run the ZR1 oil-water heat exchanger. That puts the right side cat right next to the starter, not two inches away. So that might explain a breakdown in the wiring. Assuming I can get it working right again, I'll get some insulation down there to try to keep some of that heat off.

One person said they just rigged up a new direct connection, in 4 gauge wire, from the battery to the alternator. I can see where it could run, and it would be easy enough to add a connector to fit to the alternator. How do you get the wire connected to the hot post on the battery?? Splice into the big wire going to the starter? That would be a BIG splice.

Thanks everyone. Well, and assuming I can get all this to repeat a few more times, to make sure I really got it sussed.

Workin'.

 

Just put a ring terminal on each end and connect to the bolt on the fuse box where the wire from the battery is connected

 

Well, laid out and installed the new wire. I thought I'd go ahead and clear all the codes, but my reader said there was none! Weird, as they were there before. Anyway, warmed it up, and it popped the first couple issues right on cue.

Maybe I wired it to the wrong point? I only see the one obvious hot wire on the fenderwell side of the fuse box, is there another underneath or something? I didn't see ANY wire coming over the fusebox from the battery. I may go back and splice it into the main hot wire instead.

Enough for one day, other things to do. Thoughts and opinions always welcome!

 

when you open the fusebox cover the junp terminal is wher to hook it it is a large bolt sticking right up, big red wire from there down to the starter ans another to the battery, the one to the starter may be wrapped with a loom.

 

In spite of all the developments, this is still my first choice in the list of possible solutions.

 

So, a list of clues and things tried:

The voltage stayed nice and true all the time, even when everything was going to hell. That made me think the alternator likely was NOT the culprit.

Replaced the battery, as the incumbent one was three years old anyway, and cleaned the connections. That didn't help.

I took it to the local dealer (Classic Chevy in Sugar Land). They opened the hood, we had a chat, and the service manager said no way, waaaay too Frankenstein, too much aftermarket, they were afraid they would screw something up. So no help from them.

What I finally understood from the group (cause I am not the quickest at some things), the way the car runs power from the battery to the starter to the alternator to the main fuse block under the hood, one fat wire goes from the battery hot post to the starter, then from there two additional wires head off to the alternator and the fuse block. Troubles with any of these three wires, as well as the connection at the starter, can be a likely culprit.

I purchased a voltmeter, and checked resistance while the wires were all warmed up. I could not easily get to the starter, but I could get to the battery, fuse block, and alternator. A check showed very low resistance from alternator to battery, but a virtually dead connection from battery to fuse block. Once it cooled just a little bit, then juice was flowing again.

So, got under the car and tried to pull the starter. I have ZR1 exhaust and cats, and the right side cat sits just a couple inches from the starter. I unbolted the starter, but couldn't get it out, not without removing the cat first (which was exactly what the service manual said as well, duh). I noted the starter had a lot of old oil on it, likely from when I was having issues with a rear seal when I first installed the blower long ago. I put the starter back in, and took it for a drive. This time it took a LOT longer to get it to screw up, had to get the car fully warmed up. No doubt moving around the starter moved the wires at that connection.

So, got under the car again, and sprayed a fair amount of contact cleaner all over the starter connection, to try to get it clean. While I was under there, I pulled all the speed sensors and checked them. They all looked pretty clean, but I gave them a little spraying anyway. One sensor was still firmly held in place by its clips, two were wiggling around quite a bit, and one was completely loose. I reattached it. The little clips don't seem to last very well.

Took it out again, drove it around for half an hour, including several good pulls, nada, no problems at all, check engine light cleared. So, I THINK we are good.

But at least solved for the moment. At some point I need to pull that cat and starter, and properly clean and re-install the connection at the starter.

We shall see. Thanks again for all the knowledge. Beats the hell out of the dealer!