Info - Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns
| Subject: | Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns |
| Models: | 2001-2007 Chevrolet Silverado Pickup (Classic) Models |
| 2001-2007 GMC Sierra Pickup (Classic) Models |
| with Allison® Automatic Transmission |
This bulletin is being revised to add the 2007 model year. Please discard Corporate Bulletin Number 01-03-10-010E (Section 03 -- Suspension).
Proper diagnosis of engine, transmission, speedometer and cruise control concerns must begin with an inspection of tire/wheel size.
| • | The 2500 series trucks have LT245/75R16E tires as standard equipment. |
| • | The 3500 series trucks with dual rear wheels have LT215/85R16D tires as standard equipment. |
| • | The 3500 series trucks with single rear wheels have LT265/75R16E tires as standard equipment. |
A truck that has different tires and wheels will have engine power/performance concerns, transmission shift concerns, speedometer registered speed concerns, cruise control concerns and increased steering effort, especially during parking lot maneuvers at slow speeds.
Before any diagnosis is performed for these types of concerns, inspect the tires/wheels for the proper tire and wheel combinations.
If a truck is found to have other than the above listed tire sizes, no further diagnosis should be undertaken until the original size tires and wheels are reinstalled on the truck.
The Engine Control Unit (ECM) and Transmission Control Module (TCM) use (RPM) and (VSS) inputs as operational parameters for engine torque, transmission shifting, cruise control operation and speedometer indicated vehicle speed.
Calibrations for different tire/wheel combinations are not available.
Therefore, changing of tire and/or wheel size should not be undertaken by dealerships or truck owners.
Warranty Information
Reinstalling the proper wheels and tires on the vehicle, prior to performing any type of diagnosis of the truck, would be considered truck owner responsibility and not a warranty repair.
