P0479Generic code

P0479 Code: Exhaust Pressure Control Valve Intermittent

The P0479 code indicates intermittent dropouts in the exhaust pressure control valve circuit. Expect a loss of power, slow warm-up when cold and high exhaust temperature. Loose pins, a wire broken inside its insulation or a worn relay are the usual suspects.

Severity
Medium
Can I keep driving?
Yes, but with caution
Estimated cost
$80 to $900
Difficulty
Medium
System
Emissions Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0479 code means

On some diesels (Ford Power Stroke, International) a valve in the exhaust partly closes when the engine is cold to raise the engine load and warm it up sooner. It also helps the cabin heater.

The computer monitors the control circuit from its own driver transistor. The P0479 code indicates intermittent dropouts in the circuit. Before replacing the component, check the fuse, relay, connector and wiring, since they are the most common cause.

If the valve sticks closed, the engine loses a lot of power and runs hot. If it sticks open, the engine is slow to warm up. It often seizes up with soot and rust.

Intermittent faults are found by reproducing them. With the engine running and the scan tool in graph mode, move the wiring harness section by section, tap the connector gently and, if needed, warm the area with a hair dryer or wet the connector with a spray bottle. The point where the reading jumps is the point of the fault.

P0479 code symptoms

  • Check engine light on.
  • Loss of power.
  • Slow warm-up when cold.
  • High exhaust temperature.

Likely causes of the P0479 code

  1. Bad contact, with loose or corroded pins in the connector.
  2. Wire broken inside: the insulation looks intact but the copper is split.
  3. Relay with worn contacts that sometimes does not close.

How to diagnose the P0479 code step by step

  1. Command the component with the scan tool and check whether it responds.
  2. Check the fuse and relay.
  3. Measure the supply at the connector: battery voltage with the key on or when it is commanded.
  4. Measure the component resistance and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity and for shorts.
  6. Command the valve with the scan tool and watch the exhaust pressure.
  7. Inspect the exhaust pressure sensor tube.

How to fix the P0479 code

  • Repair the connector, the wiring or the power supply.
  • Replace the exhaust pressure control valve if it does not respond with correct power and control.
  • Clear the codes and verify that the monitor completes.

Technical reference data

  • Electric or vacuum actuator controlled by PWM.
  • Approximate values only: check the manufacturer data for your engine.

Brand-specific notes

This valve is found on some turbo diesels, and soot is hard on it.

P0479 on Ford

Typical of the Ford Power Stroke 6.0 and 6.4.

P0479 on International

Typical of International engines.

Frequently asked questions about P0479

Can I drive with a P0479 code?
With caution, and keep an eye on engine temperature and power. A P0479 code can leave the valve stuck closed, and that makes the engine run hot.
What does the exhaust pressure control valve do?
On some diesels (Ford Power Stroke, International) a valve in the exhaust partly closes when cold to raise the engine load and warm it up sooner. It also helps the cabin heater.
Do I always have to replace the part?
No. Check the fuses, relays, connectors and wiring first.
How much does it cost to fix P0479?
Roughly $80 to $900, depending on whether it is wiring, a relay or the valve itself.
What does the P0479 code mean?
It is a generic OBD2 code for intermittent dropouts in the control circuit of the exhaust pressure control valve.
What is the most common cause of P0479?
A bad contact in the connector, a wire broken inside its insulation, or a relay with worn contacts. Wiggling the harness with the scan tool in graph mode usually shows where.

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