Automatic Transmission - Diagnosis - Allison: Overview GMC Sierra 2500

Test Description

The numbers listed below refer to step numbers in the diagnostic procedure

1. 1 This step determines if the scan tool is receiving power through the DLC connector.
2. 2 The MIL should illuminate whenever the ignition is on and the engine is not running.
3. 3 This step determines if the TCM is transmitting class 2 serial data to the DLC and that the class 2 data circuit is not open or shorted.
4. 4 This step determines if a DTC is current or stored in history.