Circuit Description

WARNING: This page is about a different car, the 2000 Isuzu Hombre. However, it is still accessible from the selected car via links, so may be relevant.

PCM detects engine misfire by detecting variations in crankshaft speed 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.

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 at greater than a predetermined threshold, this information is sent to PCM via Electronic Brake Control Module (ECBM) serial data circuit. PCM can then take the rough road 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 P1380 will also set, indicating rough road data was not available during misfire calculation due to ABS system malfunction.

Conditions for setting this DTC are:

A Misfire DTC (P0300-P0304) has been set.
Vehicle speed is greater than one MPH.
MAP is less than 99 kPa.
Engine speed is less than 3400 RPM.
An ABS DTC is set.