Problem after speedo recalibration

[tjwong]

I am tuning a 2004 GMC Sierra with a 4.8L. My customer had his gears changed from 3.42 to 4.10 ratio. I was successful in recalibrating the speedo which is easy to do. But, once I changed the calibration to make the speedo work, the EBTCM ( electronic brake traction control module) set a DTC and disabled the traction control and ABS. I feel the reason is because the new trucks uses the VSS for its speed input from the rear tires, instead of having individual wheel speed sensors. It still has the individual speed sensors on the left and right front wheels.

I think that the EBTCM communicates with the PCM and it compares the calibration values. Once you change either the final gear ratio or the speedometer PPM constants it will set a DTC C0279 and disable the ABS and the traction control. I tried everything I could think of to make it work. The speedo works fine, but the ABS and Traction control is disabled because of the calibration change.

So I changed it back so that the speedo is in error but the ABS and Traction control is functional. I felt this was the safest mode for me (liability wise) and the customer. DTC C0279 is incorrect calibration.

Anyone else run into this problem with a gear change over?

[rattle]

you induced a 15% or greater speed difference between one or more sensors that last for more than 3 minutes (4.10 gear will do that for ya).

what you will have to do is contact chevy dealer, have them call stg and get a VCI number released, Then have the dealer download the new calibration for the truck from the GM server and reprogram the EBCM.

Thats about the only way your going to have accurate speedo and functional ABS.

Sorry

One other way, go to wrecking yard and find truck with 4.10 gear and pull the ebcm off it.

[tjwong]

you induced a 15% or greater speed difference between one or more sensors that last for more than 3 minutes (4.10 gear will do that for ya).

what you will have to do is contact chevy dealer, have them call stg and get a VCI number released, Then have the dealer download the new calibration for the truck from the GM server and reprogram the EBCM.

Thats about the only way your going to have accurate speedo and functional ABS.

Sorry

One other way, go to wrecking yard and find truck with 4.10 gear and pull the ebcm off it.

We tried that route. Jerks at STG won't help us! I have a direct GM contact and he couldn't get it done.