P071A
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
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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.
* Engine speed is greater than 500 RPM for 5 seconds.
* Ignition voltage is 8-18 volts.
Conditions for Setting the DTC
BCM detects the Tow Mode switch has been continually activated for 10 minutes.
Action Taken When the DTC Sets
DTC P071A is a Type C DTC.
TCM inhibits tow haul activation
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 6T70/6T75 - Automatic Transmission
Connector End View Reference
Component Connector End Views Sunshade - Left Front
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.
2. Verify the Tow/Haul Mode parameter changes between Active/Inactive each time the S74 tow/haul mode switch is pressed.
• If the parameter does not change from Inactive to Active, or Active to Inactive
Refer to Circuit/System Testing below.
• If the parameter changes from Inactive to Active, or Active to Inactive
3. After performing the above steps, verify that the DTC does not reset by operating the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions you observe from the Freeze Frame/Failure Records data. If the vehicle passes the Circuit/System Verification procedure, then STOP. Do not perform the Circuit/System Testing or Component Testing as this may result in an unnecessary part replacement. Refer to Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections.
Circuit/System Testing
1. Ignition Off, transmission in Park, disconnect the S74 Tow/Haul mode switch connector.
2. Test for less than 5 ohms between the S74 Tow/Haul mode switch harness connector terminal 2 and ground.
• If 5 ohms or greater
Test for less than 2 ohms in the ground circuit, end to end.
• If 2 ohms or greater, repair the open/high resistance in ground circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection
• If less than 5 ohms
3. Ignition On.
4. Install and remove a fused jumper between the S74 Tow/Haul mode switch harness connector terminals 1 and 2. Verify the scan tool Tow/Haul Mode parameter changes from Active to Inactive or Inactive to Active each time the fuse jumper is installed.
• If the parameter does not change from Inactive to Active, or Active to Inactive
Test the signal circuit for open high resistance or a short to ground.
• If signal has open high/resistance or a short to ground, repair the signal circuit.
• If an open/high resistance or a short to ground is not found, replace the K9 body control module.
• If the parameter changes from Inactive to Active, or Active to Inactive
5. Replace the Tow/Haul switch.
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