GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Denali 🢒 Transmission/Transaxle 🢒 Automatic Transmission - Allison 🢒 DTC P1761 or P1762

Circuit Description

The transmission control module (TCM) continuously monitors the alive rolling count generated in the body control module (BCM). If the TCM detects errors in the alive rolling count, monitored through the serial data bus, DTC P1761 or P1762 set. DTC P1761 and P1762 are type C DTCs.

DTC Descriptor

This diagnostic procedure supports the following DTCs:

    • DTC P1761 Up Down Shift Switch Signal Circuit
    • DTC P1762 Transmission Mode Switch Signal Circuit

Conditions for Running The DTC
    • Engine speed is 200-7500 RPM for 5 seconds.
    • Ignition voltage is 9-18 volts.

Conditions for Setting The DTC

The TCM detects 5 error counts out of 10 samples within 10 seconds.

Action Taken When the DTC Sets

P1761

    • The TCM does not request the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL).
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM records this information as a Failure Record.
    • The TCM stores DTC P1761 in TCM history.

P1762

    • The TCM does not request the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL).
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM records this information as a Failure Record.
    • The TCM stores DTC P1762 in TCM history.

Conditions for Clearing the DTC
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring.
    • A scan tool can clear the DTC.

Step

Action

Values

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: 

       • Before clearing the DTC, use the scan tool in order to record the ECM and the TCM Failure Records. Using the Clear Info function erases the Failure Records from the ECM and TCM.
       • Using the Clear Info function erases stored DTCs in both the ECM and TCM.

  3. Record the Freeze Frame/Failure Records
  4. Clear the DTC.
  5. Ignition OFF for 30 seconds.
  6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

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Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Is the action complete?

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Go to Step 4

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4

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
  4. Select Specific DTC.
  5. Enter DTC.

Has the test run and passed?

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Go to Step 5

Go to Step 2

5

With the scan tool, observe the stored information, capture info and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

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Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK