What it means
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.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EGR A system controls valve movement and uses position feedback to report how far the valve has traveled. P0404 sets when the valve's movement or feedback does not match the expected range or commanded position, which can happen when carbon restricts travel, the sensor drifts, or the valve is mechanically damaged.
Common causes
Most likely first.
- Carbon buildup on EGR valve
- Position sensor drift
- Mechanical valve damage
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
How to diagnose it
- Save freeze-frame data and compare commanded EGR position with position feedback across the conditions that set the code.
- Inspect the EGR valve and passages for carbon that could restrict its travel.
- Check the valve connector and wiring for loose terminals, corrosion, or damage that could disrupt position feedback.
- Use a scan-tool actuator test, if available, to move the EGR valve through its range and watch whether feedback follows smoothly.
- If movement is free but feedback remains inaccurate, test the position sensor and valve assembly against the manufacturer's procedure.
Common fixes
- Clean carbon deposits that are preventing the EGR valve from moving through its range.
- Repair damaged wiring or connector terminals affecting EGR position feedback.
- Replace a position sensor that fails its specified range or tracking test.
- Replace a mechanically damaged or sticking EGR valve.
Can I keep driving?
A short, gentle trip may be possible if the engine runs normally, but avoid heavy load if it pings or hesitates. Incorrect EGR operation can increase emissions and worsen drivability.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.