P0402
PowertrainEGR Flow Excessive Detected
The exhaust gas recirculation (EGR) system is flowing more exhaust gas back into the intake than the ECU has commanded. The EGR valve may be stuck partially open, or the position sensor may be misreporting closed when it's actually flowing.
ⓘ Information only. This page provides general educational information about fault code P0402. 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 P0402 mean?
P0402 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: EGR Flow Excessive Detected.
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, sometimes a noticeable hunt or surge at low revs
- • Hesitation under acceleration, particularly noticeable on diesels
- • Poor fuel economy
- • Sometimes a slight smell of unburned fuel from the exhaust
- • On petrol cars: pinging or knock under load (excess EGR drops combustion temperature, then in some conditions causes detonation)
Possible causes
Causes commonly associated with P0402, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. EGR valve stuck partially open, often from carbon buildup that prevents the valve closing fully
- 2. Failed EGR valve actuator, the actuator can't close the valve fully even when commanded
- 3. Position sensor reading inaccurate, valve is closed but sensor reports open
- 4. Wiring fault to the EGR valve or sensor
- 5. On vacuum-operated EGR systems: a leaking vacuum line letting the valve open without command
- 6. Internal valve seal failure, modulating diaphragms can age and leak
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 EGR commanded vs actual position, the gap tells you whether the valve is responding correctly
- 2. Remove the EGR valve and inspect for carbon buildup that might be preventing full closure
- 3. Try cleaning if accessible (EGR cleaner spray £8) and check whether the valve seats properly when commanded closed
- 4. Test the actuator electrically against spec, resistance and operation against manufacturer values
- 5. Check vacuum lines on cars that use vacuum control
- 6. If cleaning doesn't help, valve replacement is the typical fix
Common questions about P0402
Difference between P0401 and P0402? +
Opposite faults on the same system. P0401 is insufficient EGR flow (valve stuck closed or passages blocked). P0402 is excessive EGR flow (valve stuck open). Diagnostic approach is similar but P0402 means the valve is letting more gas through than commanded, while P0401 means less. Both usually clear with valve cleaning or replacement.
Can I delete the EGR system? +
Tampering with emissions equipment makes the car illegal for road use and an automatic MOT failure for vehicles from 2018 onwards. Some workshops offer EGR delete services but they're not legal for road cars. Clean or replace is the proper fix.
How urgent is this? +
Medium urgency. Drivability is fine in the short term but worsens over weeks. On petrol engines particularly, prolonged operation with excess EGR can cause pinging that damages pistons over time. Address within a few weeks rather than ignoring for months.
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 →