Circuit Description
The 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 antilock 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 ECM by the electronic brake control module (EBCM) through pulse width modulation (PWM) serial data line. The 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 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1381 Misfire Detected - No Communication With Brake Control Module
Conditions for Setting the DTC
| • | Engine run time is greater than or equal to 10 seconds |
| • | PWM signal is between 5 or greater than 98% (ABS system fault). |
| • | 15 test failures between 31 test samples. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffers. |
| • | 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. |
| • | Disconnecting the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
The setting of this DTC indicates that a misfire was detected and that the ECM could not determine if the detected misfire was true or due to operating the vehicle on a rough surface. A misfire can be true misfire with or without setting this DTC. Check the EBCM for poor connections at the PWM serial data terminals. Be sure no true misfire exists after repairing the cause of this DTC.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Diagnostic System Check - ABS in Antilock Brake System |
