For 1990-2009 cars

### Circuit Description

The PCM detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. For accurate detection of engine misfire the PCM must distinguish between crankshaft deceleration caused by actual misfire and deceleration caused by rough road conditions. The ABS Brake System can detect if the vehicle is on a rough road based on wheel acceleration/deceleration data supplied by the wheel speed sensors. If the ABS system detects rough road above a predetermined threshold, this information is sent to the PCM via serial data. The PCM can then take the rough road into account when calculating misfire. Even if the ABS is malfunctioning and cannot detect rough roads, the misfire diagnostic will continue to run. However, if a misfire DTC sets, this additional DTC also sets indicating that rough road data was not available during the misfire calculation due to an ABS System malfunction.

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0121, P0122, P0123, P0335, P0336, P0742 not set.

• | The vehicle speed is greater than 10.0 mph.

• | The engine load is less than 60%.

• | The engine misfire is detected (DTC P0300 set).

• | The engine speed is less than 3200 RPM.

### Conditions for Setting the DTC

An ABS system malfunction exists preventing the PCM from receiving rough road detection data.

### Action Taken When the DTC Sets

• | The powertrain control module (PCM) stores the DTC information into memory when the diagnostic runs and fails.

• | The malfunction indicator lamp (MIL) will not illuminate.

• | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A last test failed, or current DTC, clears when the diagnostic runs and does not fail.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Use a scan tool in order to clear the MIL and the DTC.

### Diagnostic Aids

Important:

• | Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM.

• | For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

• | Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed.

• | For an intermittent condition, refer to Symptoms .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. Service the ABS system before diagnosing for a misfire, because an actual engine misfire may or may not exist. The following two examples illustrate how this DTC can be set with or without an actual engine misfire:

• | There was an actual engine misfire during an ABS system malfunction.

• | The vehicle operator drove on a rough road, the ABS system could not detect this due to a malfunction, and the PCM interpreted the variations in crankshaft speed caused by the rough road as a misfire.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Diagnostic System Check - ABS in Antilock Brake System. | Go to Powertrain On Board Diagnostic (OBD) System Check