Inaccurate Speedometer - keywords cluster erratic gauge IPC odometer VSS

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Owners may comment on the speedometer being inaccurate. This could be caused by an incorrect PCM/ECM speed calibration.

Install The Tech 2 and Build As Follows:

F0: Diagnostics

Year

Medium Duty Truck

Make (Chevrolet or GMC)

D- C Series

F0: Powertrain

Select Proper "Engine Size"

Select Proper "Transmissions Type"

F2: Special Functions

F0: Engine Output Controls

F9: Speed Cal. Reprogramming

F1: Reprogram Speed Calibration

Then Enter The Proper "Axle Ratio" And "RPM".

Vehicles with 225/70R19.5 tires enter "641" for the RPM.

Vehicles with 245/70R19.5 tires enter "622" for the RPM.

Note: If when performing the above procedure and the below message is displayed on the Tech 2 or if the vehicle is equipped with an 8.1L L18 engine, follow the programming procedure outline in eSI Document ID 1549751.

"No reprogramming information have been stored on the Tech 2. Follow instruction in service manual on the proper procedure of reprogramming the speed calibration."

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.