Capteur de route dégradée défectueux

The sensor telling the module the road surface is rough, faulty so the module cannot distinguish surface-induced crankshaft speed variation from a genuine misfire. Misfire detection works by measuring tiny fluctuations in crankshaft speed, and a rough road shakes the driveline enough to produce fluctuations that look exactly like one.

So the sensor exists to suppress false misfire reports, and losing it costs accuracy in both directions. Without a trustworthy signal the module either disables misfire monitoring — so a real misfire goes unreported and the converter is unprotected — or reports misfires the engine is not having. False misfire codes that appear only on poor surfaces are this sensor, and the correlation with road conditions is the diagnostic clue.

Not every vehicle has a dedicated sensor; many derive the same information from the braking module's wheel speeds, which is why these codes often accompany a communication fault rather than a sensor fault. Establish which arrangement the vehicle uses before looking for a part — on a derived system there is no rough road sensor to replace, and the fault is in the data path.