Between my brother and I we have 3 corvettes. Two z06's 01 and 04 and a 99 6 speed coupe. The 99 has given my brother some problems for quite some time now. At first, his service traction light, service abs, and low coolant were all displaying on the cluster. Coolant was fine by the way. Low coolant stopped coming on but service abs and traction control still displayed sometimes, sometimes not. Most of us would think it's the EBCM. However, recently he changed the rear tires to a 275/35/18 and since after about a minute of driving, the car depowers to only 28 mph and a display like excessive speed displays. Also, since he has changed the rear tires, the service abs and service traction control lights have gone out and no longer display. Now with the traction control turned off, the car drives fine. My brother is thinking that it is because he downsized the rear tires, however on my 04 z06 I have 19" CCW's with a 335/30/19 and have no problems. Also, he let the car sit for about a month as he was driving the Z but once a week would take the car up the street to keep the battery charged and car running. One night we came out to run up the street and when passing by the car we noticed that the Air Conditioning lights were lit up, which was very odd as nothing was left on. Since it has drained the battery. First thing we are replacing is the battery, but then what. Our local Chevy dealer has a bunch of morons working for them so we won't take it there. I'm thinking the car has a bad ECU. I pulled it tonight to see if maybe something had shorted or had any noticable signs of failure, but everything looked ok. Any ideas on what to do with the car? He doesn't mind spending money on the car, but we don't know where to start. Thanks in advance for any replies.

 

The first thing you should do is pull the codes and see what its complaining about. I know on the '99 that the PCM has a tire size programming item in there but I thought it was only for speedometer calibration, however, its not in the BCM, rather its in the PCM. So who knows, you might need to alter that setting. For the other things, ground connections are one of the primary causes of problems...so clean them up and verify they are working properly.