EGR Valve
What it is
The Exhaust Gas Recirculation (EGR) valve routes a small, measured amount of exhaust gas back into the intake. It is a common carbon-clogging point on both petrol and diesel engines.
What it does
By recirculating inert exhaust gas it lowers combustion temperature, which cuts nitrogen-oxide (NOx) emissions and reduces engine knock. When it sticks open it causes rough idling and stalling; stuck closed or clogged it raises NOx and sets P0401/P0402.
Symptoms of failure
- P0401 (insufficient flow) or P0402 (excessive flow) codes
- Rough idle or stalling at stops
- Engine knock or pinging
- Failed emissions test (high NOx)
- Hesitation under light acceleration
Common fault codes
Which vehicles need it
Most petrol and diesel engines with EGR. Carbon build-up is especially common on high-mileage and short-trip vehicles.
Replacement cost
| DIY (part only) | $40–$200 |
|---|---|
| At a shop (parts + labor) | $200–$600 |
| Replacement interval | No set interval — clean carbon periodically; replace when it sticks or fails electrically. |
| DIY difficulty | Moderate (DIY) — often bolt-on and cleanable, but access can be tight |
| Recommended brands | Standard Motor Products, Delphi, Dorman, OEM |
Where to buy the part
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Frequently asked questions
Can I clean an EGR valve instead of replacing it?
Often yes. Many EGR codes are caused by carbon, not a dead valve. Removing it and cleaning the passages with carbon cleaner fixes a lot of P0401 cases — try that before buying a new valve.
Is it safe to drive with an EGR fault?
Usually short-term, but the engine may idle roughly, knock, or fail emissions. Persistent knock can cause real damage, so do not ignore it for long.