P0479
Exhaust Pressure Control Valve A Intermittent
Exhaust / back-pressure control
Generic OBD-II
Medium
What it means
P0479 means the exhaust pressure (back-pressure) control valve "A" is behaving intermittently — the ECM sees its position or operation drop out and return. This valve regulates exhaust back-pressure, often for the exhaust brake and warm-up on diesels. The vehicle usually still drives, but power delivery and engine braking can be inconsistent until the sticking valve or wiring fault is fixed.
Medium
Can I keep driving? Usually drivable, but on diesels the exhaust brake and power delivery may be inconsistent, so have it looked at before it becomes a hard fault.
Common symptoms
What you'll notice
- Check-engine light on
- Intermittent loss of power or inconsistent boost
- Weak or erratic engine (exhaust) braking on diesels
- May enter a reduced-power limp mode at times
Common causes
Most likely first
- Exhaust pressure control valve sticking from carbon or sootLikely
- Intermittent wiring fault or loose connector in the valve circuitCommon
- Faulty valve actuator or motorCommon
- Corroded connector at the valveLess often
- Failed ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data to see when the fault appears.
- Wiggle-test the valve wiring and connector for an intermittent open or short.
- Inspect and clean the valve for carbon/soot binding.
- Test the actuator's operation and replace the valve or actuator if it sticks, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0479?+
Short trips are usually fine, but power and engine braking may be inconsistent. Fix it before it sticks fully open or closed.
Can I just clear P0479?+
An intermittent fault may stay away briefly, but it returns until the valve or its wiring is repaired.
Related codes
Often seen with P0479
Read & clear P0479 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX