6L45/6L50/6L80/6L90 - Automatic Transmission

DTC P071A

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.

DTC Descriptor
DTC P071A
- Transmission Tow Mode Switch Circuit

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.

Conditions for Running the DTC

* DTC P1762 is not set.
* The engine speed is greater than 400 RPM for 5 seconds.
* The ignition voltage is 8.6 volts or greater.

Conditions for Setting the DTC

The Tow/Haul Mode switch remains closed, in a low voltage condition, for 10 seconds.

Action Taken When the DTC Sets

DTC P071A is a Type C DTC.

Conditions for Clearing the DTC

DTC P071A is a Type C DTC.

Diagnostic Aids

If the electrical circuit tests are OK and the shift pattern is not occurring, there may be a mechanical/hydraulic condition that prevents operation. Refer to Symptoms - Automatic Transmission (Symptoms - Automatic Transmission).

Reference Information
Schematic Reference

Automatic Transmission Controls Schematics (6L45/6L50/6L80/6L90 - 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)

Description and Operation

Electronic Component Description (Electronic Component Description)
DTC Type Reference

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

Control Module References (Programming and Relearning)for scan tool information

Circuit/System Verification

1. Ignition ON, cycle the Tow/Haul switch while observing the Tow/Haul switch parameter on the scan tool in the Transmission Controls Data list. The Tow/Haul switch parameter should change states from NO to YES, or YES to NO with each cycle of the switch.
2. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Circuit/System Testing

1. Ignition OFF, transmission in Park. Disconnect the automatic transmission shift lever electrical connector.
2. Ignition OFF, test for less than 1 ohm between terminal 2 on the automatic transmission shift lever vehicle harness connector and ground at the battery negative post.

• If greater than the specified value, test the ground circuit for an open/high resistance.

3. Ignition ON, test for greater than 11 volts on the signal circuit terminal 1 on the automatic transmission shift lever vehicle harness connector and ground at the battery negative post.

• If not within the specified value, test the signal circuit for a short to ground or an open/high resistance. If all circuits test normal, replace the BCM.

4. Ignition OFF, test for less than 3 ohms between terminal 1 and terminal 2 on the automatic transmission shift lever component harness connector while depressing the Tow/Haul switch button.

• If greater than the specified value, replace the automatic transmission shift lever assembly.

5. If all circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.

* Control Module References (Programming and Relearning)for BCM replacement, setup, and programming.
* Automatic Transmission Range Selector Lever Replacement (Automatic Transmission Range Selector Lever Replacement)