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. If the ABS detects a rough road above a predetermined
threshold, this information is sent to the PCM via
serial data. 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,
this additional DTC also sets indicating that rough
road data was not available during the misfire calculation
due to an ABS malfunction.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0121, P0122, P0123, P0335, P0336, and
P0742 are not set. |
| • | The vehicle speed is more than 16 km/h (10 mph). |
| • | The engine load is less than 60 percent. |
| • | The engine misfire is detected and DTC P0300 is set. |
| • | The engine speed is less than 3200 RPM. |
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.
-
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:
| • | 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. |
