Description of On-Board Diagnostics

GENERAL DIAGNOSIS INFORMATION
The 42RE is an electronically controlled transmission. Shift points and sequence are controlled by the Transmission Control Module (TCM). Before attempting repair, determine if a malfunction is electrical or mechanical.

The TCM used with the 42RE transmission has a self-diagnostic program that is compatible with the DRB III tester. The tester will identify faults in the electrical control system. A schematic of the TCM circuitry is provided. The diagnosis information in this section will help locate faults in the transmission running gear.

Diagnosis should begin with the Preliminary Check Procedure. It will help determine if a problem is mechanical or electrical. The first procedure step is Initial Inspection and Adjustment.