DTC P1380: EBCM DTC Detected Rough Road Data Unstable: Description

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Powertrain Control Module (PCM) detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. For accurate detection of engine misfire, PCM must distinguish between crankshaft deceleration caused by actual misfire and deceleration caused by rough road conditions. Anti-lock Brake System (ABS) can detect if vehicle is on a rough road based on wheel acceleration or deceleration data supplied by wheel speed sensors. If ABS detects rough road more than a predetermined threshold, this information is sent to PCM via serial data. PCM can then take 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 sets, this additional DTC also sets indicating that rough road data was not available during misfire calculation due to an ABS malfunction.