Circuit Description
Correct engine misfire detection is dependent on whether or not the vehicle is experiencing a rough road condition. A rough road condition causes unexpected crankshaft fluctuations. In order to detect a rough road condition, the electronic brake control
module (EBCM) communicates a wheel speed signal over the serial data circuit to the engine control module (ECM). The wheel speed sensor information allows the ECM to distinguish if the crankshaft speed variations are caused by a rough road condition or are
caused by a true misfire. If the EBCM reports a wheel speed sensor failure, or the ECM does not receive the rough road information, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC.
DTC P0318 Rough Road Sensor Circuit
Conditions for Running the DTC
| • | The ignition is ON or the engine is operating. |
| • | DTC P0318 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
| • | The EBCM reports a wheel speed sensor failure to the ECM. |
| • | The ECM does not receive communication of a rough road signal from the EBCM for more than 5 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
| • | A condition with a wheel speed sensor will cause this DTC to set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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A condition with the wheel speed sensors or the serial data circuits between the EBCM and ECM can cause this DTC.
