Tow/Haul Switch/Indicator Always On or Inoperative

Tow/Haul Switch/Indicator Always On or Inoperative

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

Circuit/System 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 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.

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 Symptoms - Automatic Transmission (Symptoms - Automatic Transmission).

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (4L60-E/4L65-E/4L70-E - Automatic Transmission)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Transmission Control Module Scan Tool Information (4L60-E) (Transmission Control Module Scan Tool Information (4L60-E)) Transmission Control Module Scan Tool Information (6L45/6L50/6L80/6L90) (Transmission Control Module Scan Tool Information (6L45/6L50/6L80/6L90))

Circuit/System Verification

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.

Circuit/System Testing

1. Ignition OFF, transmission in PARK or NEUTRAL, disconnect the Tow/Haul switch connector.
2. Test for less than 1 ohm of resistance between the Tow/Haul switch signal circuit terminal B and ground.

• If greater than the specified range, test the ground circuit for an Open/High resistance.

3. Ignition ON, verify the scan tool parameter Park/Neutral displays INACTIVE.

• If not the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a fused jumper between the signal circuit and ground. Verify the scan tool parameter displays ACTIVE.

• 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.

5. If all circuits test normal, replace the Tow/Haul switch.

Component Testing

1. Ignition OFF, transmission in PARK or NEUTRAL, disconnect the transmission Tow/Haul switch assembly.
2. Test for infinite resistance between the Tow/Haul switch with the switch in the OPEN position.

• 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.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Body Control Module (BCM) assembly replacement. Refer to Control Module References (Programming and Relearning) for BCM replacement, setup, and programming
* Perform the Shift Lever Replacement (Shift Lever Replacement).