P0477 code meaning
Exhaust Pressure Control Valve A Low
Powertrain system Generic code P04xx codes Check engine light
What P0477 means
The exhaust pressure control valve is a flap in the exhaust: on older Navistar/Ford diesels a warm-up flap that raises back pressure when cold, on Ram and others an exhaust brake, on VW's 2.0 TDI a flap that drives the low-pressure EGR, and on Audi and Bentley a sound flap. P0477 means the control circuit of valve A is low. Audi uses it for a short to ground of the exhaust flap. VW's 2.0 TDI of 2009–12 sets it together with P047F, P048A–P048C and P0401 when salt has corroded the flap shaft and the flap sticks – a blocked motor can cause overcurrent or a voltage drop; on the 2015 engine it appears with P0478/P0475 and the actuator is replaced.
P0477 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0477
- Check engine light on
- Flap without function: sound unchanged, rattling
- Diesel: longer warm-up, exhaust brake weak or EGR faults
Common causes of P0477
- Most likelyControl wire shorted to ground
- Most likelyFlap actuator faulty internally
- PossibleFlap seized by corrosion (motor blocked)
- PossibleChafed wire at the underbody
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Exhaust pressure control valve aValve actuatorActuator wiringEngine control module
What each part of P0477 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 77 | The exact fault in that area. |
What to do next
- Note P0477 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0477
What does P0477 mean?
P0477 means "Exhaust Pressure Control Valve A Low". The exhaust pressure control valve is a flap in the exhaust: on older Navistar/Ford diesels a warm-up flap that raises back pressure when cold, on Ram and others an exhaust brake, on VW's 2.0 TDI a flap that drives the low-pressure EGR, and on Audi and Bentley a sound flap. It is a generic code, so it means the same on every make.
Is it safe to drive with P0477?
Drive gently and only to a workshop. With P0477 the car can go into limp mode (reduced power) to protect itself.
Will P0477 fail an emissions test?
Yes, it can. P0477 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0477 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P0477 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.