P1381

Circuit Description
The Powertrain Control Module (PCM) identifies engine misfire by detecting variations in crankshaft speed. Crankshaft speed variations can also occur when a vehicle is operated over a rough surface. The Anti-Lock Brake System (ABS) can detect if the vehicle is on a rough surface based on wheel acceleration/deceleration data supplied by each wheel speed sensor. This information is sent to the PCM by the Electronic Brake Control Module (EBCM) over the UART serial data line. The PCM then uses this information to determine if the crankshaft variations are being caused by an actual engine misfire or from being driven on a rough surface.
If the ABS is found to be malfunctioning, the PCM will still continue to detect for misfire. However, if a misfire DTC is set, this additional DTC will also be set, indicating that rough surface data was not usable during the misfire detection due to the ABS malfunction.

Conditions for Setting the DTC
- A DTC P0300-P0304 has been set
- Vehicle speed is greater than 1 mph (2 km/h)
- Manifold Absolute Pressure (MAP) is below 99.7 kPa
- Engine speed is below 3406 RPM

Action Taken When the DTC Sets
- The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer.
- A history DTC is stored.

Conditions for Clearing the DTC
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- DTCs can be cleared by using a scan tool.

Diagnostic Aids
The setting of this DTC indicates that a misfire was detected and that the PCM could not determine if the detected misfire was true or due to operating the vehicle on a rough surface. A misfire can be a true misfire with or without selling this DTC. Check the EBCM for poor connections at the UART serial data terminals. Be sure no true misfire exists after repairing the cause of this DTC.

DTC P1381 - Misfire Detected - No EBCM/PCM Serial Data:

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.
3. Be careful to clear only DTCs and not the captured information stored on the scan tool. The scan tool will issue a warning if this is about to happen.
4. Refer to the ABS portion of the service manual for ABS DTCs and repairs. Performing the ABS Diagnostic System Check is the first step in diagnosing a serial data problem.
5. A DTC P1381 being reset indicates that the PCM is not receiving serial data from the EBCM due to a EBCM problem.
6. When DTC P1381 is set, ABS serial data should not be able to be displayed.
7. Repair any condition that is causing a misfire by following the table for any DTC that has set.
8. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.