For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provide an overview of each diagnostic category.

### DTC Descriptor

DTC P0318: Rough Road Sensor Circuit

### Circuit Description

Correct engine misfire detection is dependent on whether or not the vehicle is experiencing a rough road condition. A rough road condition causes unexpected crankshaft fluctuations. In order to detect a rough road condition, the electronic brake control module (EBCM) communicates a wheel speed signal over the serial data circuit to the engine control module (ECM). The wheel speed sensor information allows the ECM to distinguish if the crankshaft speed variations are caused by a rough road condition or are caused by a true misfire. If the EBCM reports a wheel speed sensor failure, or the ECM does not receive the rough road information, this DTC sets.

### Conditions for Running the DTC

• | The ignition is ON or the engine is operating.

• | DTC P0318 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

• | The EBCM reports a wheel speed sensor failure to the ECM.

| OR

• | The ECM does not receive communication of a rough road signal from the EBCM for greater than 5 seconds.

### Action Taken When the DTC Sets

DTC P0318 is a Type B DTC.

### Conditions for Clearing the DTC

DTC P0318 is a Type B DTC.

### Reference Information

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

Engine idling, observe the scan tool DTC information.

Important: If any UXXXX DTCs are set, diagnose those first.

⇒ | If DTC P0318 failed this ignition, refer to Diagnostic Starting Point - Antilock Brake System.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine control module replacement, setup, and programming