• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
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 transmission control module (TCM) 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. The tow/haul switch is a momentary switch and is normally open. The internal spring in the switch will always cause the switch state to return to open when not held in to the closed position.
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 Symptoms - Automatic Transmission.
Automatic Transmission Controls Schematics
Transmission General Description
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Transmission Control Module Scan Tool Information
With a scan tool observe the Tow/Haul switch parameter. Operate the Tow/Haul switch several times, and observe the parameter as you operate the switch with the transmission in DRIVE. The parameter should toggle between ACTIVE and INACTIVE when the switch is operated.
⇒ | If greater than the specified range, test the ground circuit for an Open/High resistance. |
⇒ | If not the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM. |
⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the Tow/Haul switch assembly. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Body Control Module (BCM) assembly replacement. Refer to Control Module References for replacement, setup, and programming