I've seen where this problem has been posted before, but didn't see any conclusive answer other than "take it to the dealer". Can anyone help? 2004 Avalanche the ABS and Brake warning lights come on, the speedo goes nuts sometimes even reading 25 MPH standing still, many times the trans will not shift out of low, the speed controled auto door lock function screws up, locking the doors with truck at rest (been locked out twice!), sometimes get a "service4WD warning". Is this a instrument cluster modual problem? wheel speed sensors? body computer? Bad wiring connections? What ??? I fixed a ABS light problem on my 05' Uplander by just cleaning the weather pac connectors to each wheel speed sensor, could this be samekind of problemwith the Avalanche?
Joe B

 

You need to take a look at the vss (vehicle speed sensor). It contrals the speedometer and shifting of the trans and I believe it is use far the traction control system along with abs. Also you should have the alternator test if it has a bad diode it could leak AC current into the electrical system because the vss uses AC current a bad alt could mess with the signal.

 

Thanks to MDTAHOE... problem seems to be fixed. Thereappears to be two VSS sensors on the tail shaft housing. I changed the one on the left side and cleaned the weather pack connectors on both sensors.The warninglights have not come back on...so far!
The VSS sensor came from NAPA # VSS239

Anyone know why the two sensors and what function eachpreform ?

Joe B