GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Holden 🢒 2005 🢒 Caprice WL 🢒 DTC 🢒 DTC P1793

Circuit Description

The Engine Control Module (ECM) sends wheel speed data to the Transmission Control Module (TCM). The data is sent to the TCM through a communication network called the GM Controller Area Network (GMLAN). Two circuits are used to communicate GMLAN data between the ECM/TCM and other modules. A fault in the GMLAN will not cause DTC P1793 to set by itself. If a GMLAN fault occurs, other DTCs will set before DTC P1793.

When the TCM receives a invalid wheel speed data from the ECM, then DTC P1793 will set, which is a type 'C' DTC.

Conditions for Running the DTC
    • Ignition voltage is between 8.0 and 18.0 volts.
    • Engine is running between 450 and 6,800 RPM for at least 5 seconds.
    • No other GMLAN errors are present.

Conditions for Setting the DTC

The TCM receives no valid wheel speed data from the ECM for 2 seconds.

Action Taken When the DTC Sets
    • The TCM records the operating conditions when the 'Conditions for Setting the DTC' have been met. The TCM stores this information as a failure record.
    • The TCM does not request the Powertrain Interface Module (PIM) to illuminate the Check Powertrain Malfunction Indicator Lamp (MIL).
    • The TCM stores DTC P1793 into TCM history.

Conditions for Clearing the MIL/DTC
    • Tech 2 can clear the DTC.
    • The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring.
    • The TCM cancels the default actions when the ignition is off long enough to power down the TCM.

Step

Action

Values

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

For information on testing wiring faults, refer to Wiring Systems.

1

Has the Diagnostic System Check - Automatic Transmission been completed?

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Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2
  1. Connect Tech 2 to the DLC.
  2. Ignition ON, engine OFF.
  3. Record any ECM DTCs.

Did you record any ECM DTCs?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3
  1. Clear the DTC.
  2. Turn the ignition off for at least 30 seconds.
  3. Start engine and allow to idle.

Did DTC P1793 reset?

--

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections

4

Did any other DTCs set?

--

Go to the Vehicle System Diagnostics that belongs to the undiagnosed DTC

Go to Step 5

5

Replace TCM. Refer to Transmission Control Module Replacement.

Is the replacement complete?

--

Go to Step 6

--

6
  1. Perform the following operation to verify the repair:
    2. 1.1. Select DTC on the Tech 2.
    1.2. Select 'Clear info'.
  2. Operate the vehicle in the Conditions for Running the DTC.

Has the test run and passed?

--

System OK

Go to Step 2

When all diagnosis and repairs are completed, clear all DTCs and verify correct operation.