For 1990-2009 cars

### 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 controller area network (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P1793 to set by itself. If a CAN fault occurs, other DTCs will set before DTC P1793.

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

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1793 Wheel Speed Signal

### Conditions for Running the DTC

• | The engine run time is at least 6 seconds.

• | No other CAN 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 does not request the ECM to illuminate the malfunction indicator lamp (MIL).

• | The TCM inhibits Autograde braking.

• | The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.

• | The TCM stores DTC P1793 in TCM history.

### Conditions for Clearing the DTC

• | A scan tool can clear 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.

• | The TCM cancels the DTC default actions when the ignition is OFF long enough in order to power down the TCM.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | 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.

Important: Record all Failure Records before clearing the DTC. Using Clear Info erases the Failure Records from the ECM and TCM.

3. Record the DTC Failure Records.

Did you record any ECM Failure Records?

--

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, and allow the engine 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 Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 5
5 | Replace the TCM. Refer to Control Module References for replacement, setup and programming. Is the action complete? | -- | Go to Step 6 | --
6 | Perform the following operation to verify the repair:

1. Select DTC on the scan tool.
2. Select Clear Info.
3. Start, and allow the engine to idle.
4. Select Specific DTC.
5. Enter DTC P1793.

Has the test run and passed?

--

Go to Step 7

Go to Step 2

7 | 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? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK