System Description
The powertrain control module (PCM) detects engine misfire events by monitoring
variations in the crankshaft rotation speed. Wheel speed changes caused by rough
road conditions can cause changes in crankshaft speed. By monitoring the wheel speed
sensors, the anti-lock brake system (ABS) can determine if the vehicle is operating
on a rough road. If the ABS is detecting a rough road condition severe enough to effect
misfire detection, a rough road signal is sent to the PCM on the serial data circuit.
If DTC P0300 is set and the rough road information is not available due to
an ABS malfunction, DTC P1380 will set.
Conditions for Running the DTC
| • | The vehicle speed is more than 1 km/h (0.6 mph). |
| • | The engine load is less than 100 percent. |
| • | The engine misfire is detected--DTC P0300 set. |
| • | The engine speed is less than 6,500 RPM. |
Conditions for Setting the DTC
An ABS malfunction exists preventing the PCM from receiving 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. |
