P0404
EGR Range/Performance
The EGR valve does not move through its expected range or its position feedback does not track command. The valve may be sticking, the position sensor may be drifting or carbon buildup is preventing full travel.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- Carbon buildup on EGR valveCommon
- Position sensor driftPossible
- Mechanical valve damageLess likely
Parts involved
- EGR Valve
- EGR Position Sensor
P0404 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.