There's two parts to this saga, the background and then the info I got recently from a mechanic.

BACKGROUND:

I've got a 2001 Chevy Cavalier that I drive about one day a week. The rest of the time I ride my scooter everywhere. I've had this car for about 4 years now and it's been nothing but great to me. I do all the oil changes myself as well as brakes and I've tried to take good care of the engine and transmission. It's got about 145 thousand miles on it.

About 2 years ago it started doing this weird thing. Basically I'll be driving and for no apparent reason the "low trac" light will come on. This is the light that comes on when the tires are spinning out, for example on snow. Not the light that comes on when the emergency brake is pulled up, that's the "trac off" light.

When this light comes on, suddenly the car will start revving really high when shifting up from gear to gear, and when it does shift, it slams into the next gear really hard. It should be noted that the gears aren't slipping at all, they're just shifting really hard from gear to gear, not smoothly like they normally do.

After doing this for about 5 to 10 minutes the car will eventually just sputter and die.

Now, when it first started doing this I'd just pull over. Turn the car off and start it back up and it would be fine. But lately it's been getting worse. Granted, it only does this once every few months, but the last time it did this, 2 weeks ago, the check engine light came on along with the low trac light, and the car wouldn't start without the check engine light coming on unless I waited about an hour and a half.

Recent developments:

Yesterday I took it to my mechanic, a really good guy who I trust and who does great work. I described everything to him but I warned him that I couldn't really tell him how to replicate the problem. It just happens.

After leaving it with him for the day he said they drove it around a bunch and couldn't get it to do it. They hooked it up to the computer and, here's the weird part: there were no codes. Nada.

I know for a fact that the check engine light came on quite a few times so there should at least be something in the logs about that but they said there was nothing coming from the computer at all. He said that might be an indication that the computer in the car might be going bad. I asked him if a bad computer might be causing the problem that I'm describing and he said it's possible because the transmission is shifted via computer, but he said that there's really no way to tell without tearing the whole car apart. In his words "it seems like this is just a problem that's going to have to get worse before it can get better".




So what do you guys think? Ever hear of something like this before? Does my mechanics opinion sound right?

Thanks.

One time when I accidentally forgot to tighten the alternator wires, that happened as the battery went dead. The car would rev, shift hard and the transmission shifted in weird patterns. Check your alternator cables for corosion, they might just be coroded enough for it to happen sometimes.


*2000 Cavalier sedan*

This might be another dead end, but I immediately thought of the checking the large round plug-in wiring harness on the front of the transmission. This is the one that's down a bit, on the driver's side near the battery (at least on my older 1997 2.2 -- I've never looked on other newer cavys.) This is the harness that gets mucked with for "shift improver" type products, such as the ShiftPlus or Autotrans Interceptor. One of the parameters affected is transmission line pressure, resulting in harder shifts. One of the side effects of too much pressure is that you can cause the TRAC light to appear. I'd yank that plug off to make sure it's clean and tightly connected, and that there is no corrosion or damage to the plug or wires.




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