P1381

P1381 ABS Rough Road Serial Data Fault

Circuit Description
The powertrain control module (PCM)/engine control module (ECM) identifies engine misfire by detecting variations in crankshaft speed. Crankshaft speed variations can also occur when a vehicle is operated over a rough road. The Anti-Lock Brake System (ABS) can detect it 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/ECM by the Electronic Brake Control Module EBCM through the Instrument Panel Cluster (IPC) over the Universal Asynchronous Receiver Transmitter (UART) serial data line. The PCM/ECM 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/ECM will still continue to detect for misfire. However, if a misfire Diagnostic Trouble Code (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
- No message has been received in a time period greater than 5 seconds.
- The vehicle speed is greater than or equal to 8 mph (13 kph).
- The engine speed is less than or equal to 5100 rpm.
- Misfire option load is selected and the engine load is less than 93.8%.

Action Taken When the DTC Sets
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- DTCs can be cleared by using a scan tool.
- A history DTC is stored.

Conditions for Clearing the MIL/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/ECM 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 setting this DTC. Check the IPC and the EBCM for poor connections at the UART serial data terminals. Be sure no true misfire exists after repairing the cause of this DTC. A DTC P1618 also indicates that a fault may lie within the IPC serial data line, its connections, or within the IPC.

Step 1 - 9:

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. The On-Board Diagnostic (OBD II) 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 malfunction occurred. The information is then stored on the scan tool for later reference.
2. 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. A DTC P1381 being reset indicates that the PCM/ECM is not receiving the correct information from the EBCM due to an ABS DTC.
5. When DTC P1381 is set, an ABS DTC should also be set.
6. Repair any condition that remains and is causing a misfire by following the table for any DTC that has set.
7. The replacement PCM/ECM must be reprogrammed. Refer to the latest Techline procedure for PCM/ECM reprogramming.