Circuit Description
The powertrain control module (PCM) uses the rough road information to enhance the misfire diagnostic by distinguishing crankshaft speed variations caused by driving on rough road surfaces from variations caused by true misfires. The electronic brake control module (EBCM) transmits rough road information based on inputs from the wheel speed sensors, to the body control module (BCM). The BCM acts as a bus and sends this information via a UART serial data circuit to the powertrain interface module (PIM). The PIM converts the UART serial data to Class II serial data for sharing with the PCM. A loss of serial data communication will cause the PCM not to receive rough road information. If a loss of communication with the EBCM occurs while engine misfire conditions exist to set DTC P0300, DTC P1381 will also set.
DTC Descriptors
This diagnostic procedure supports the following DTC.
DTC P1381 Misfire Detected - No Communication With Brake Control Module
Conditions for Running the DTC
| • | Engine load is less than 87 percent. |
| • | Engine speed is less than 5,000 RPM. |
| • | Vehicle speed is greater than 16 km/h (10 mph). |
| • | An engine misfire is detected and DTC P0300 is active. |
| • | DTC P1381 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The PCM is detecting a loss of communication with the EBCM for at least 5 seconds.
Action Taken When the DTC Sets
| • | The PCM stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Use a scan tool in order to clear the DTC. |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
Ensures that the EBCM is capable of transmitting serial data to the data link connector (DLC).
-
This test determines if the fault is in the Class II serial data circuit between the PCM and the PIM.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
Can ABS data be displayed? | Go to Step 3 | Go to Scan Tool Does Not Communicate with UART Data Line in Data Link Communications | |
Test the serial data circuit for an open or a poor connection between the PCM and the powertrain interface module (PIM). Refer to Testing for Continuity , and Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 4 | Go to Diagnostic System Check - ABS in Antilock Brake System | |
4 |
Does the DTC run and pass | Go to Step 5 | Go to Step 2 |
5 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
