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 changes in crankshaft speed caused by actual misfire or by rough road conditions. ABS system can detect if vehicle is on a rough road based on wheel acceleration/deceleration data supplied by wheel speed sensors. If ABS system detects rough road greater than a predetermined threshold, this information is sent to PCM via Class 2 serial data circuit. PCM can then take rough roads into account when calculating misfire.

Even if ABS is malfunctioning and cannot detect rough roads, misfire diagnostic will continue to run. However, if a misfire DTC is set, this additional DTC P1381 will also set, indicating that rough road data was not available during misfire calculation due to ABS system malfunction.

Condition required for setting this DTC is; PCM received no serial data information for 15 seconds since previous data was received.