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 Descriptors

DTC P1380: Misfire Detected - Rough Road Data Not Available
DTC P1381: Misfire Detected - No Communication with Brake Control Module

### System Description

The engine control module (ECM) detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. For accurate detection of engine misfire, the ECM must distinguish between crankshaft deceleration caused by actual misfire and deceleration caused by rough road conditions. The antilock brake system (ABS) 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 detects rough road above predetermined threshold, this information is sent to the ECM. The ECM uses the rough road information when calculating engine misfire. If the ABS is malfunctioning and cannot detect rough roads, the misfire diagnostic will continue to run; however, if an engine misfire DTC sets, this DTC also sets indicating that rough road data was not available, or there was no communication with the brake control module during the misfire calculation due to an ABS malfunction.

### Conditions for Running the DTC

• | The vehicle speed is greater than 8 km/h (5 mph).

• | The engine speed is less than 7,000 RPM.

• | The engine load is less than 60 percent.

• | Engine misfire is detected and DTC P0300 sets with the MIL illuminated.

• | DTCs P1380 and P1381 run continuously when the above conditions are met.

### Conditions for Setting the DTC

#### P1380

• | The ABS controller sends a message to the ECM indicating that a failure has occurred in the ABS module.

• | Engine misfire is detected and DTC P0300 set.

#### P1381

• | An ABS malfunction exists for more than 10 seconds, preventing the ECM from receiving rough road detection data.

• | Engine misfire is detected and DTC P0300 set.

### Action Taken When the DTC Sets

DTCs P1380 and P1381 are Type C DTCs.

### Conditions for Clearing the DTC

DTCs P1380 and P1381 are Type C DTCs.

### Reference Information

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Monitor the ABS DTCs on the scan tool.

⇒ | If any ABS DTCs are set, diagnose those first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle

⇒ | If there are no ABS DTCs set, refer to the following:

Symptoms - Antilock Brake System