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 GMLAN. Two circuits are used to communicate GMLAN data between the ECM and TCM. 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 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 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 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 | |
2 |
Important: Record all Failure Records before clearing the DTC. Using Clear Info erases the Failure Records from the ECM and TCM. Did you record any ECM Failure Records? | -- | Go to Step 3 | |
3 |
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 Step 5 | |
5 | Replace the TCM. Refer to Control Module References for replacement, set-up and programming. Is the action complete? | -- | Go to Step 6 | -- |
6 | Perform the following operation to verify the repair:
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? | -- | System OK |
