2003 8.1 With Allison?

[1320jon]

I had a friend with his 2003 2500 stop by. Its lifted with 40's and 5.13's. Anyways the pcm is progammed for a 4l80e, but it has a 5 speed allison? Changing tranny tables does nothing, so I ve concluded that when they option the allison, they run a seperate tranny pcm? The truck has a abs /brake system failure, but the speed is correct, and the speed sensor is on the output of the transfer case. It only has abs on the front. So I dont think it should have an error at all? Its not comparing frnt and rear wheel speed. Is it the allison gear ratios? Or just the and incorrect gear ratio/tire size for out put shaft speed calculation?

 

It originally had 29.8 tires and 373's now it has 39's (as measured) and 5.13's, whicj is very very close to the the oem set up.

 

Any ideas on how to over come the abs error?

[chpspecial]

I have that same truck, and yes it has a seperate TCM/PCM combo. the trans parameters are null on the PCM side of things. You can still use the speedo settings in the PCM side of things to correct for the tire size. In my experience a little change in tire size can cause ABS to go nuts. If you find someone with EFILive, or HPTunners, get them to set the tire size/gear combo, as close as possible. Then use the speedo fine tunning section to dial in the true speed of the truck vs. the displayed speed on the speedometer (you will need an external speed device for this i.e. GPS). It can be a correction factor of 1% and will be enough to correct the ABS problem. At least in the few truck that have given me these problems.

 

It could also be a sensor cable that you guys might have missed when doing the gears/tire change.

[zippy]

Changing the trans tables should still do whatever you tell it. The codes are because the ABS module reads off the rear output speed sensor and the speed sensor in the front wheel hub bearings. If you correct the info for the transmission control module it will read correctly, but the front is going to be way off yet causing the problem you're getting. The only way to change the front abs reading is with a tech 2 and the largest tire calibration it will go to is for a 265/75R16 tire which is way short of what you have. There is no fix for the abs problem since nobody has hacked the abs module calibration that I know of. You have the choice of an abs issue and a correct speedo or and incorrect speedo and no abs problem.