I recently changed the ECU on my car. The new ECU has been reprogrammed to my engine tune. The problem I have now is that the transmission will not shift into overdrive most of the time. The way I can get it to work sometimes is to restart the car. What I have found is that the ECU is showing engine codes C0237 and C0240. I can't figure out why i get these codes and how to get rid of them.

 

The GM code lists for the 99 LS1 do not list either of those codes under engine or transmission.

http://service.gm.com/gmspo/mode6/

 

C0237 - Rear Wheel Speed Signal Erratic

C0240 PCM Traction Control Not Allowed

The main thing, is the trans not going into overdrive. I don't know if it is from these codes or something else. Through HP tuners, the tuner can manually lock up the converter, but only sometimes, otherwise the ECU won't even send the signal to lock up. He cleared the codes and the trans worked fine for about 5 minutes, then as soon as the codes came back, the trans wouldn't lock up.

 

Those are neither engine or tranny codes. They are for the EBTCM. Have you checked the rear wheel ABS/TCS sensors?

 

I haven't looked at those yet.

Would those going bad cause the EBTCM to not let the trans shift to overdrive?

 

Here's what the problem is, I took a GPS and compared it to the car, what I found is that the speedometer is 2% off, the trip meter is 2% off and the difference between 26" tires and 25.5" tires is 2%. The computer thinks there are 26" tires but they are really 25.5"

What is happening is the trans is reporting one speed, but the ABS/TCS is reading a different speed, so the conflict is turning off the overdrive. If i turn off the TCS, the car goes into overdrive with no problems.

 

The rear wheel ABS/TCS sensors will be "off" by the same % as the tranny output shaft (VSS), if its the tire diameter that is programmed incorrectly. Why not try having the correct tire diameter programmed into the PCM, and see if that helps.

 

Well, on Sunday I had "worked" with my tuner, and the tire diameter at the time skip our minds. I will have him adjust that later on this month when I swap out my cam and retune the car.