Circuit Description

PCM detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. 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.

The ABS system can detect if vehicle is on a rough road based on wheel acceleration/deceleration data supplied by the wheel speed sensors. If ABS system detects rough road above a predetermined threshold, this information is sent to the PCM via the serial data (UART). 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.

Conditions for setting this DTC are as follows:

• Vehicle speed is more than one MPH.
• Map is less than 99 kPa.
• DTC P0300-P0304 has been set.
• Engine speed is less than 3400 RPM.
• An ABS DTC is set.