Circuit Description

PCM receives rough road information from the EBCM/EBTCM on the Class II serial data circuit. 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.

Conditions for setting this DTC are as follows:

• Engine load less than 87 percent.
• Vehicle speed is greater than 10 MPH.
• Engine speed is less than 5000 RPM.
• A misfire DTC is occurring and requesting MIL to be illuminated.
• PCM has detected a rough road data error for at least 5 seconds.