Winter Mode Switch/Indicator Always On or Inoperative

Winter Mode Switch/Indicator Always On or Inoperative

Circuit Description

The winter mode allows the driver selection of a third gear start in order to reduce wheel spin under low traction conditions. Winter mode programming in the transmission control module (TCM) will command the 1-2 shift solenoid On and the 2-3 and 4-5 solenoids Off, enabling third gear for greater traction. The winter mode switch is a console mounted momentary contact switch located on the electronic PRNDL assembly. Accessory voltage is supplied to the electronic PRNDL assembly through the ELEC PRNDL fuse. When the winter mode switch is depressed, it momentarily contacts the switch signal circuit. The rear integration module (RIM) recognizes the voltage on the circuit and sends a class 2 serial data message to the dash integration module (DIM). The DIM sends a class 2 message to the engine control module (ECM). The ECM sends a request to the transmission control module (TCM) through the controller area network (CAN) to enable the winter mode program.

The TCM evaluates the request, and if operating conditions are correct for enabling the program, the TCM sends a confirmation message to the ECM. The ECM then requests the instrument panel cluster (IPC) to illuminate the winter mode indicator.

The winter mode feature remains enabled until the mode switch is pressed again, the transmission is placed in a lower gear, and certain vehicle speed, transmission fluid temperature, or accelerator pedal positions are exceeded. Once disabled, the TCM will resume a normal shift pattern.

Diagnostic Aids

* Test the instrument panel cluster (IPC) for proper operation and lamp illumination. Refer to Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview).
* Test the rear integration module (RIM) for proper winter mode switch input and output operation. Refer to Body Control System Description and Operation (Description and Operation).

Test Description

The numbers below refer to the step numbers on the diagnostic table.
1. Diagnose all communication and body DTCs first. The DTC may be the source of the symptom.
4. No PRNDL display could be open in the electronic PRNDL assembly accessory circuit.
6. This step tests the winter mode circuit by bypassing the electronic PRNDL assembly.