P0477 Code: Exhaust Pressure Control Valve A Low
🟠 Moderate severity · drivable
Drivable, but the engine may start hard in cold weather and idle rough; fix it soon.
What P0477 means
The engine computer sees the exhaust pressure control valve reading too low, meaning the valve is not building the expected exhaust backpressure. A low reading usually comes from a valve stuck open, a leaking control line, or a failing actuator. Without proper backpressure, the engine warms up slower and may run roughly.
Symptoms
- Check engine light is on
- Hard starting in cold weather
- Rough idle
- Exhaust smoke on startup
Common causes
- most common: Valve stuck in the open position
- common: Leaking vacuum line or control hose
- common: Weak or failed valve actuator
- less common: Faulty valve position sensor
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Check and replace leaking vacuum or control lines | Yes | $20–100 |
| Clean or replace the stuck valve | Yes | $100–350 |
| Replace the valve actuator or position sensor | Mechanic | $150–400 |
Frequently asked questions
Can I drive with a P0477 code?
Yes, but the engine may be harder to start in cold weather and idle rough. Have the valve system inspected soon.
What does a low exhaust pressure control reading mean?
It means the valve is not closing enough to build backpressure, often because it is stuck open or a control line is leaking.
How much does it cost to fix a P0477?
A vacuum line fix is $20–$100. Replacing the valve or actuator typically runs $100–$400.
Related codes
P0475
P0475 Code: Exhaust Pressure Control Valve A Malfunction
P0476P0476 Code: Exhaust Pressure Control Valve A Range/Performance
P0478P0478 Code: Exhaust Pressure Control Valve A High
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.