DTC P0318: Rough Road Sensor Circuit: Description

WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Correct engine misfire detection is dependent on whether or not the vehicle is experiencing a rough road condition. A rough road condition will cause unexpected crankshaft fluctuations especially when the torque converter clutch is in its lockup state. In order to detect a rough road condition, the ECM will use vehicle speed information from the Right Front Wheel Speed Sensor (RFWSS) available on both ABS and non-ABS vehicles. On ABS vehicles, the Electronic Brake and Traction Control Module (EBTCM) sends the ECM RFWSS signal information over the Controller Area Network (CAN) link. On non-ABS vehicles, the ECM receives this information over a discrete wire from the wheel speed signal conditioner module. This module converts the AC signal from the RFWSS to a square wave by momentarily grounding White wire. The ECM contains an internal 12 volt pull-up voltage supplied to White wire necessary to detect a square wave of 0 to 12 volts. DTC P0318 will set if the ECM does not detect a sufficient rough road signal based on the vehicle speed from the RFWSS when the vehicle is traveling in 4th or 5th gear for a certain length of time. If the ECM does not receive a rough road signal, it will not detect misfire.