Transmission Mode Switch: Testing and Inspection

Tow/Haul Switch/Indicator Always On or Inoperative






Circuit Description
Tow/haul mode enables the operator to achieve enhanced shift performance when towing or hauling a load. When tow/haul mode is selected, the tow/haul switch input signal to the body control module (BCM) is momentarily toggled to zero volts. This signals the vehicle control module (VCM) to extend the length of time between upshifts and increase transmission line pressure. Cycling the tow/haul switch again disables tow/haul mode and returns the transmission to a normal shift pattern.

Diagnostic Aids
Inspect the connectors at the BCM, and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Diagrams/Diagnostic Aids.
Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Diagrams/Diagnostic Aids.
If the electrical circuit checks are OK and the tow/haul shift pattern is not occurring, there may be a mechanical/hydraulic condition that prevents tow/haul operation. Refer to Symptom Diagnosis.






Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for a faulty tow/haul switch.
3. This step tests for voltage input from the BCM to the tow/haul switch.