For 1990-2009 cars
Engine Controls Components
Power, Ground, MIL, DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The PCM receives rough road information from the EBCM / EBTCM on the UART 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 / EBTCM transmits rough road information based on inputs from the wheel speed sensors. If a loss of communication occurs which causes the PCM not to receive rough road information while DTC P0300 is requesting the MIL, DTC P1381 will set.

### Conditions for Running the DTC

• | Engine load is less than 87%.

• | Engine speed is less than 5000 RPM.

• | Vehicle speed is greater than 10 mph.

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

### Conditions for Setting the DTC

The PCM is detecting a loss of communication with the EBCM / EBTCM for at least 5 seconds.

### Action Taken When the DTC Sets

• | The PCM will not illuminate the Malfunction Indicator Lamp (MIL).

• | The PCM will store conditions which were present when the DTC set as Fail Records data only. This information will not be stored as Freeze Frame data.

### Conditions for Clearing the MIL/DTC

• | A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

### Diagnostic Aids

Check for the following conditions:

• | Poor connection at the PCM or at the EBCM / EBTCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe ABS data on the scan tool while moving connectors and wiring harnesses related to the EBCM / EBTCM. A loss of ABS data will indicate the location of the malfunction.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

### Test Description

Number(s) below refer to the step number(s) 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 | Was the Powertrain OBD System Check performed? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 | Operate the vehicle at a speed greater than 5 km/h (3 mph). Does DTC C1275 set? | -- | Go to DTC C1275 Serial Data Malfunction in Antilock Brake System | Go to Intermittents and Poor Connections Diagnosis in Wiring Systems