For 1990-2009 cars

Refer to Engine Controls Schematics .

### Circuit Description

The powertrain control module (PCM) receives rough road information from the electronic brake control module (EBCM) on the Class II serial data circuit. The PCM uses the rough road information to enhance the misfire diagnostic by distinguishing crankshaft speed variations caused by driving on rough road surfaces from variations caused by true misfires. The EBCM transmits rough road information based on inputs from the wheel speed sensors. If a loss of communication occurs which causes the PCM to not receive rough road information while DTC P0300 is requesting the malfunction indicator lamp (MIL) DTC P1381 is set.

### Conditions for Running the DTC

• | The engine load is less than 87 percent.

• | The engine speed is less than 5000 RPM.

• | The vehicle speed is greater than 10 mph.

• | A misfire DTC is occurring and requesting that the MIL be illuminated.

### Conditions for Setting the DTC

The PCM detects a loss of communication with the EBCM for at least 5 seconds.

### Action Taken When the DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

### Conditions for Clearing the MIL/DTC

• | The DTC becomes history when the conditions for setting the DTC are no longer present.

• | The history DTC clears after 40 malfunction free warm-up cycles.

• | The PCM receives a clear code command from the scan tool.

### Diagnostic Aids

Inspect for the following conditions:

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

### Test Description

Numbers below refer to the step numbers on the Diagnostic Table:

1. Ensures that the EBCM/EBTCM is capable of transmitting serial data on the serial data circuit.

#### DTC P1381 - Misfire Detected - No EBCM/PCM Serial Data

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn on the ignition switch.
2. Attempt to display ABS data on the scan tool.

Can ABS data be displayed?

--

Go to Diagnostic System Check - ABS in Antilock Brake System

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications