Circuit Description

PCM detects engine misfire by detecting variations in crankshaft speed. For accurate detection of engine misfire, PCM must be able to distinguish between crankshaft deceleration caused by actual misfire or deceleration caused by rough road conditions.

ABS system can detect if vehicle is on a rough road based on wheel acceleration/deceleration data supplied by each wheel speed sensor. If ABS system detects rough road greater than a predetermined threshold, this information is sent to the PCM via the Electronic Brake Control Module (EBCM) serial data circuit. PCM can then take the rough road into account when calculating misfire.

Even if the ABS is malfunctioning and cannot detect rough roads, the misfire diagnostic will continue to run. However, if a misfire DTC is set, this additional DTC P1380 will also set, indicating that rough road data was not available during the misfire calculation due to ABS system malfunction.

If there are 20 unusable ABS data values within a 50 value sample, DTC will set.