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

### Circuit/System Description

The engine control module (ECM) identifies engine misfire by detecting variations in crankshaft speed. Crankshaft speed variations can also occur when a vehicle is operated over a rough road. The antilock brake system (ABS) can detect if the vehicle is on a rough surface based on wheel acceleration/deceleration data supplied by each wheel speed sensor. This information is sent to the ECM by the electronic brake control module (EBCM) through pulse width modulation (PWM) serial data line. The ECM then uses this information to determine if the crankshaft variations are being caused by an actual engine misfire or from being driven on a rough surface.

If the ABS is found to be malfunctioning, the ECM will still continue to detect for misfire. However, if a misfire DTC is set, this additional DTC will also be set, indicating that rough surface data was not usable during the misfire detection due to the ABS malfunction.

### Conditions for Running the DTC

• | Engine run time is greater than or equal to 10 seconds.

• | PWM signal is between 95-98 percent (ABS system fault).

• | The DTCs run once the above conditions are met.

### Conditions for Setting the DTC

The ECM detects 15 test failures between 31 test samples.

### 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

### Circuit/System Testing

1. DTCs P1380 or P1381 are informational DTCs. If there are no engine control DTCs, refer to No Communication with Electronic Brake Control Module .
2. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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