GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The powertrain control module (PCM) detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. For accurate detection of engine misfire, the PCM must distinguish between crankshaft deceleration caused by an 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 the wheel acceleration and deceleration data supplied by the wheel speed sensors. The ABS electronic brake control module (EBCM) transmits rough road information to the body control module (BCM). The BCM acts as a bus and sends this information via a UART serial data circuit to the powertrain interface module (PIM). The PIM converts the UART serial data to Class II serial data for sharing with the PCM. The PCM can then take the rough road into account when calculating a misfire. Even if the ABS is malfunctioning and cannot detect rough roads, the misfire diagnostic will continue to run. However, if a misfire DTC sets, DTC P1380 also sets indicating that rough road data was not available during the misfire calculation due to an ABS system malfunction.

DTC Descriptors

This diagnostic procedure supports the following DTC.

DTC P1380 Misfire Detected - Rough Road Data Not Available

Conditions for Running the DTC

    •  Engine load is less than 87 percent.
    •  Engine speed is less than 5,000 RPM.
    •  Vehicle speed is greater than 16 km/h (10 mph).
    •  An engine misfire is detected and DTC P0300 is active.
    • DTC P1380 runs continuously when the above conditions are met.

Conditions for Setting the DTC

An ABS system malfunction exists, preventing the PCM from receiving the rough road detection data.

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC

    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

For an intermittent condition, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. Service the ABS system before you diagnose for a misfire, because an actual engine misfire may or may not exist. The following examples illustrate how this DTC can be set with or without an actual engine misfire:

  2. • There was an actual engine misfire during an ABS system malfunction.
    • The vehicle operator drove on a rough road, the ABS system could not detect this due to a malfunction, and the PCM interpreted the variations in crankshaft speed caused by the rough road as a misfire.

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Diagnostic System Check - ABS in Antilock Brake System

Go to Diagnostic System Check - Engine Controls