P0479: Exhaust-pressure control valve — intermittent signal — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
The monitor for exhaust-pressure control valve reports an intermittent or unstable signal; a fault may not be present throughout a stationary check. This concerns exhaust back-pressure control, not an EGR flow diagnosis. The valve location and control arrangement depend on the engine.
Affected system: Exhaust pressure control
Symptoms
- Warning light may illuminate
- Related system function may be impaired
- Vehicle-specific symptoms vary
Possible causes
- Implausible sensor or switch signal, poor ground, connector corrosion, or wiring damage
- Related wiring, connector, power or ground fault
- Vehicle-specific mechanical or control issue
What to check
- Record stored and pending codes and freeze-frame data
- Compare the named sensor or switch signal with actual operating conditions; inspect the connector, reference supply, ground and harness.
- Confirm measured values against the vehicle service information
- Retest under the conditions that set the code
- Compare the named sensor or switch signal with actual operating conditions; inspect the connector, reference supply, ground and harness.
- Repair the verified cause and confirm the code does not return
Also written as: P0479-00, P047900, PO479 (some scan tools add the fault-type byte, e.g. -00).