Circuit Description
The powertrain control modlue (PCM) detects engine misfire by detecting
variations in the crankshaft deceleration between the firing strokes. For
accurate detection of an engine misfire, the PCM
must distinguish between a crankshaft deceleration caused
by an actual misfire and a deceleration caused by rough
road conditions. The ABS Brake System 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 system 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 serial data communication between the ABS System and the
PCM is malfunctioning and the PCM cannot receive the
rough road data, the misfire diagnostic continues
to run. If a misfire DTC sets, this additional DTC
also sets, indicating that the rough road data was not available
during the misfire calculation due to a serial data
malfunction.
Conditions for Running the DTC
| • | The vehicle speed is more than 16 km/h (10 mph). |
| • | The engine speed is below 3200 RPM. |
| • | The engine load is less than 60 percent. |
| • | An engine misfire is detected and DTC P0300 is set. |
Conditions for Setting the DTC
| • | A serial data malfunction exists, preventing the PCM from receiving
the rough road detection data. |
| • | The above conditions met for 20 seconds. |
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 diagnosing 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 condition due to a malfunction, and the PCM interpreted the
variations in the crankshaft speed caused by the rough road as
a misfire. |
