Circuit Description
The 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 actual
misfire and deceleration caused by rough road conditions. The ABS Brake
System can detect if the vehicle is on a rough road based on wheel acceleration/deceleration
data supplied by the wheel speed sensors. If the ABS system detects 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 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 System malfunction.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0335, P0336, P0742, P1120, P1121, P1220,
P1221 are not set. |
| • | The vehicle speed is above 16 km/h (10 mph). |
| • | The engine load is less than 60 percent. |
| • | Engine misfire is detected (DTC P0300 set). |
| • | The engine speed is less than 3200 RPM. |
Conditions for Setting the DTC
An ABS system malfunction exists preventing the PCM from receiving rough
road detection data.
Conditions for Clearing the MIL/DTC
| • | A last test failed, or the current DTC, clears when the diagnostic
runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles,
if failures are not reported by this or any other emission related
diagnostic. |
| • | Use a scan tool in order to clear the MIL/DTC. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after
3 consecutive ignition cycles that the diagnostic runs and does not
fail. |
| • | A last test failed, or current DTC, clears when the diagnostic
runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles,
if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Important:
| • | Remove any debris from the PCM\TAC module connector surfaces before
servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets
when diagnosing/replacing the modules. Ensure that the gaskets are
installed correctly. The gaskets prevent contaminate intrusion into
the PCM\TAC modules. |
| • | For any test that requires probing the PCM or a component
harness connector, use the Connector Test Adapter Kit J 35616
. Using this kit prevents damage
to the harness/component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems. |
| • | Using the Freeze Frame and/or Failure Records data may aid in
locating an intermittent condition. If you cannot duplicate the DTC, the information
included in the Freeze Frame and/or Failure Records data can help determine
how many miles since the DTC set. The Fail Counter and Pass Counter can
also help determine how many ignition cycles the diagnostic reported
a pass and/or a fail. Operate vehicle within the same freeze frame conditions
(RPM, load, vehicle speed, temperature etc.) that you observed. This
will isolate when the DTC failed. |
| • | For an intermittent condition, refer to
Symptoms
. |
Test Description
The numbers below refer to the step numbers 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 two 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. |
