P0318

Diagnostic Chart Part 1:

Diagnostic Chart Part 2:

Schematic:

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 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 circuit 1909. The ECM contains an internal 12 volt pull-up voltage supplied to circuit 1909 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 top gear for a certain length of time. If the ECM does not receive a rough road signal, it will still detect misfires; however, the threshold will be relaxed.

DTC PARAMETERS
DTC P0318 will set if the ECM detects the rough road signal based on the vehicle speed from the right front wheel speed sensor signal less than 5 km/h (3 mph) when:
^ Transmission is in 4th or 5th gear

OR

^ Condition exists for longer than 3 seconds
^ Vehicle is in a decel
^ ECT is greater than 64°C (147°F)
^ Engine speed is between 1800 and 3000 rpm

DTC P0318 diagnostic runs continuously once the above conditions have been met.

P0318 is a type D DTC.

DIAGNOSTIC AIDS

IMPORTANT: ABS only: If a right front wheel speed sensor circuit DTC if also set, diagnose that DTC first. An ABS DTC should also set with P0318 on an ABS vehicle. The road rough signal on an ABS vehicle is sent to the ECM from the EBTCM over the CAN link.

To locate an intermittent problem, use Scan tool to monitor DTC P0318 LAST TEST while driving the vehicle in the conditions listed under DTC parameters. A change from PASSED to FAILED indicates an error is occurring.

Another way to locate an intermittent problem is to backprobe circuit 1909 at the wheel speed conditioner module to verify the integrity of the signal to the ECM. Twelve volts should be on circuit 1909 with the ignition On and right front wheel not moving. As the wheel moves, the DVOM will fluctuate or read a lower voltage as the wheel spins. This indicates the wheel speed signal conditioner module is receiving the RFWSS signal and is momentarily grounding circuit 1909. Lifting the vehicle and allowing the engine to drive the wheels will allow easy rotation of the right front wheel.

The wheel speed conditioner module is located behind the left center console trim panel (left side of gear shift).

Right front wheel speed sensor resistance: 1k-2k ohms.