P0477

DTC P0477

CIRCUIT DESCRIPTION
The engine control module (ECM) controls the exhaust brake control relay which supplies power to the intake throttle solenoid valve and exhaust brake magnetic valve based on vehicle running condition. The ECM monitors the exhaust brake control relay operating status through the exhaust brake relay feedback circuit and the intake throttle solenoid feedback circuit. If the ECM detects a low voltage condition on the exhaust brake control relay control circuit or either of the feedback circuits when the exhaust brake is commanded ON, this DTC will set.

Condition for Running the DTC
- DTCs P0478, P0642, P0643, U0073 and U0101 are not set.
- The battery voltage is between 10-16 volts.
- The ignition switch is ON time is longer than 5 seconds.
- The engine is running.
- The exhaust brake cut is not controlled.

Condition for Setting the DTC
- The ECM detects a low voltage condition on the exhaust brake control relay control circuit for longer than 1 second.

OR
- The ECM detects a low voltage condition on the exhaust brake control relay feedback circuit or intake throttle solenoid valve feedback circuit for longer than 1.5 seconds when the exhaust brake control relay is commanded ON.

Action Taken When the DTC Sets
- The ECM illuminates the malfunction indicator lamp (MIL) on the second consecutive driving cycle when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Freeze Frame/Failure Records on the second consecutive driving cycle when the diagnostic runs and fails.
- The ECM inhibits the cruise control.

Condition for Clearing the MIL/DTC
- The ECM turns OFF the MIL after 3 consecutive driving cycles when the diagnostic runs and does not fail.
- 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 emission related diagnostic after the ECM turns OFF the MIL.
- Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
If an intermittent condition is suspected, the following may cause an intermittent:
- Faulty exhaust brake control relay
- Poor connections
- Misrouted harness
- Rubbed through wire insulation
- Broken wire inside the insulation

Check for the following conditions:
- Poor connection at the ECM: Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness: Inspect the wiring harness for damage. If the harness appears to be OK, observe the "Exhaust Brake Relay" or "Intake Throttle Solenoid" display on the scan tool with engine running while moving connectors and wiring harness. A change in the display will indicate the location of the fault.

NOTE: If the exhaust brake control relay control circuit is open circuit, DTC P0478 will also set.

DTC P0477
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls Connector End Views or Engine Control Module (ECM) Connector End Views

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