Rough Road Detection

The misfire detection monitor may include a rough road detection system to eliminate false misfire indications due to rough road conditions. The rough road detection system uses data from the anti-lock brake system (ABS) wheel speed sensors for estimating the severity of rough road conditions. This is a more direct measurement of rough road over other methods which are based on drive line feedback via crankshaft velocity measurements. It improves accuracy over these other methods since it eliminates interactions with actual misfire.

In the event of a rough road detection system failure, the rough road detection output is ignored and the misfire detection monitor remains active. A rough road detection system failure could be caused by a failure in any of the input signals to the algorithm. This includes the ABS wheel speed sensors, brake pedal position (BPP) switch, or controller area network (CAN) hardware concerns. Specific DTCs indicate the source of these component concerns.

A redundant check is also carried out on the rough road detection system to verify it is not stuck high due to other unforeseen causes. If the rough road detection system indicates rough road during low vehicle speed conditions where it is not expected, the rough road detection output is ignored and the misfire monitor remains active.