For 1990-2009 cars

Refer to Antilock Brake System Schematics in ABS Brakes.

### Circuit Description

The PCM receives rough road information from the EBCM / EBTCM on the Class 2 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 10 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 Failure 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.

• | The DTC can be cleared by using the scan tool Clear Info function.

### 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 Freeze Frame/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 UART serial data circuit.

2. Tests the UART serial data circuit at the EBCM/EBTCM for correct voltage.

#### 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 performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn ON the ignition.
2. With a scan tool, attempt to display ABS data.

Can ABS data be displayed?

--

Go to Step 3

Go to Step 4

3 | Test the serial data circuit for an open or a faulty connection. Refer to Wiring Repairs or Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | System OK | Go to Diagnostic Aids
4 |

1. Turn OFF the ignition.
2. Disconnect the EBTCM.
3. Turn ON the ignition.
4. Measure the voltage on the serial data circuit using a J 39200 Digital Multimeter that is connected to a good ground.

Does the voltage vary within the specified range ?

1-5V

Go to Step 5

Go to Step 6

5 | Inspect for a faulty connection at the EBTCM. Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6
6 | Test for an open in the serial data circuit to the EBTCM. Refer to Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 7 | Go to Self-Diagnostics in ABS/TCS
7 |

1. Turn ON the ignition.
2. With a scan tool, select chassis application.
3. With a scan tool, attempt to display ABS data.

Can ABS data be displayed?

--

System OK

Go to Step 4