6T40 (MH8,MHH) - Automatic Transmission

DTC P1761

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 P1761
- Up and Down Shift Switch Signal Message Counter Incorrect

Circuit/System Description

When the shift lever is placed in the M position, electronic range select or manual mode, which allows for the selection of the range of gears available, is activated. This is also known as the tap shift function. The manual mode allows the vehicle operator to increase the highest range attainable by pressing the plus (+) button or decrease the highest attainable range by pressing the minus (-) button. The body control module (BCM) supplies a signal circuit to the shift controller. The shift controller has switches connected to a resistor array. A voltage drop occurs across the resistor network. When the plus or minus button is pushed, a corresponding voltage drop occurs across the resistor network. This voltage drop is monitored by the BCM. The BCM will send the request to the transmission control module (TCM) to increase or decrease the available gear ranges. The BCM internal counter increments each time the tap shift signal status is sent and the BCM sends the rolling count with the tap shift signal status. The TCM counter increments each time the tap shift signal status is received. The DTC will set if the rolling count value of the TCM does not match the rolling count sent from the BCM.

Conditions for Running the DTC

* Engine speed is 400-7,500 RPM for 5 s.

* Runs continuously when above condition is met.

Conditions for Setting the DTC

TCM detects the internal rolling count value does not match the expected BCM count value, 3 times within 10 s.

Action Taken When the DTC Sets

* P1761 is a Type C DTC.

* TCM inhibits the Tap Up Tap Down function.

* TCM inhibits manual shifting of forward gears.

Conditions for Clearing the DTC

P1761 is a Type C DTC.

Reference Information

Schematic Reference

* Automatic Transmission Controls Schematics 6T40 (MH8,MHH) - Automatic Transmission

* Data Communication Schematics [1][2]Electrical Diagrams

* Body Control System Schematics [1][2]Body Control Systems

Connector End View Reference

* Component Connector End Views Sunshade - Left

* Inline Harness Connector End Views X110

Description and Operation

* Transmission General Description Transmission General Description

* Transmission Component and System Description Transmission Component and System Description

* Electronic Component Description Electronic Component Description

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

Control Module References Control Module References for scan tool information

Circuit/System Verification

Note:

* DTC P1761 is an informational DTC.

* Diagnose all other body control module DTCs prior to DTC P1761.

1. Verify there are no other body control module or communication DTCs set.

• If a DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

• If a DTC is not set

2. Complete the diagnosis by looking for a GMLAN circuit fault. Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with High Speed GMLAN Device.

• If a GMLAN circuit fault is found
Repair as necessary.

• If a GMLAN circuit fault is not found

3. All OK.

Repair Instructions

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

* Perform the Transmission Adaptive Values Learn 6T40 (MH8,MHH) - Automatic Transmission following all transmission repairs.

* Control Module References Control Module References for Body Control Module and Control Solenoid Valve Assembly replacement, programming and setup.