P1381

CIRCUIT DESCRIPTION
The PCM detects engine misfire by detecting variations in the crankshaft deceleration between the firing strokes. For accurate detection of an engine misfire, the PCM must distinguish between a crankshaft deceleration caused by an actual misfire and a deceleration caused by rough road conditions. The ABS Brake System can detect if the vehicle is on a rough road based on the wheel acceleration and deceleration data supplied by the wheel speed sensors. If the ABS system detects a 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 a misfire. Even if serial data communication between the ABS System and the PCM is malfunctioning and the PCM cannot receive the rough road data, the misfire diagnostic continues to run. If a misfire DTC sets, this additional DTC also sets, indicating that the rough road data was not available during the misfire calculation due to a serial data malfunction.

CONDITIONS FOR RUNNING THE DTC
^ The vehicle speed is more than 10 mph.
^ The engine speed is below 3200 RPM.
^ The engine load is less than 60 percent.
^ An engine misfire is detected and DTC P0300 is set.

CONDITIONS FOR SETTING THE DTC
^ A serial data malfunction exists, preventing the PCM from receiving the rough road detection data.
^ The above conditions met for 20 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
^ The driver information center, if equipped, may display a message.

CONDITIONS FOR CLEARING THE DTC
^ A current DTC "Last Test Failed" clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ Use a scan tool in order to clear the DTC.

DIAGNOSTIC AIDS
For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Step 1:

The number below refers to the step number 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 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 condition due to a malfunction, and the PCM interpreted the variations in the crankshaft speed caused by the rough road as a misfire.