P0404
PowertrainEGR Circuit Range/Performance
The exhaust gas recirculation (EGR) position sensor is reporting a value the ECU considers out of range. Either the EGR valve isn't actually moving when commanded, or the position feedback signal is wrong.
ⓘ Information only. This page provides general educational information about fault code P0404. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0404 mean?
P0404 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: EGR Circuit Range/Performance.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light
- • Rough idle, particularly at low revs
- • Hesitation when accelerating, more noticeable on diesels
- • Reduced power, limp mode in some cases
- • Increased emissions, possible MOT smoke test failure on diesels
- • Sometimes a slight surge or hunting at idle
Possible causes
Causes commonly associated with P0404, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. EGR valve seized from carbon buildup, almost universal on EU-emission diesels at 80,000+ miles
- 2. Failed EGR position sensor (where it's a separate part)
- 3. Sticking EGR pintle, the valve can't physically move through its full range
- 4. Wiring fault between the valve actuator and ECU
- 5. Connector contaminated with carbon, oil, or moisture
- 6. On some cars, the EGR cooler bypass valve also factors into this code
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read live data on commanded vs actual EGR position, the gap tells you whether the valve is responding to commands
- 2. Remove the EGR valve and visually inspect, carbon buildup is usually obvious and dramatic
- 3. Try cleaning if accessible, EGR cleaner spray (£8) and patience often restores function for another 20,000-50,000 miles
- 4. Test the actuator electrically against spec, resistance and operation against manufacturer values
- 5. If cleaning doesn't free the valve, replacement is the next step
- 6. On diesels, address the underlying cause (short-trip driving, carbon-heavy intake) at the same time, otherwise the new valve clogs up just as fast
Common questions about P0404
Difference between P0403 and P0404? +
P0403 is the EGR control circuit fault (electrical). P0404 is the EGR performance/range fault (the valve isn't behaving right whether the circuit is healthy or not). They sometimes appear together; the diagnostic approach is essentially the same: clean first, replace if cleaning doesn't help.
Why does my diesel keep blocking up the EGR? +
Diesel EGR systems route hot, sooty exhaust gas back into the intake. Over time, soot mixes with oil mist from crankcase ventilation and forms a hard, tar-like residue that builds up in the EGR valve, intake manifold, and around any sensors. Cars used mostly for short urban journeys (low exhaust temperatures, more soot) build up gunk fastest. An occasional sustained motorway run helps significantly.
Can I delete the EGR? +
Tampering with emissions equipment makes the car illegal for road use and an automatic MOT failure post-2018 in the UK. Some workshops offer EGR delete services but they're not legal for road cars. The proper fix is clean or replace the valve.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →