P0477Generic code

P0477 Code: Exhaust Pressure Control Valve Low

The P0477 code indicates low voltage in the control circuit of the exhaust pressure control valve, from a short to ground or a lack of power. Expect a loss of power, slow warm-up when cold and high exhaust temperature.

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

On this page

What the P0477 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 P0477 code indicates low voltage in the control circuit (a short to ground or a lack of power). 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.

To confirm it, unplug the component with the key on and watch what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is fine and the component is the one pulling the signal to ground. If it does not change, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0477 code symptoms

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

Likely causes of the P0477 code

  1. Control wire shorted to ground. The component may stay energized all the time, or the computer cuts the command to protect itself.
  2. Interrupted power supply, from a fuse or relay.
  3. Shorted component, with a resistance far lower than specified.

How to diagnose the P0477 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 P0477 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.

P0477 on Ford

Typical of the Ford Power Stroke 6.0 and 6.4.

P0477 on International

Typical of International engines.

Frequently asked questions about P0477

Can I drive with a P0477 code?
With caution, and keep an eye on engine temperature and power. A P0477 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 P0477?
Roughly $80 to $900, depending on whether it is wiring or the valve itself.
What does the P0477 code mean?
It is a generic OBD2 code that means the control circuit of the exhaust pressure control valve is reading low voltage, from a short to ground or a lack of power.
What is the most common cause of P0477?
A control wire shorted to ground, an interrupted power supply from a fuse or relay, or a shorted valve. Check the wiring and fuse before buying the valve.

Related codes

Questions about the P0477 code

There are no questions about this code yet. Tell us about your case: vehicle, symptoms and what you have already checked.