P0402 P0xxx · Powertrain (P) Medium severity
Exhaust Gas Recirculation Flow Excessive Detected
Too much exhaust gas is entering the intake. The EGR valve is stuck open or the flow signal is over-reading, starving the mixture of oxygen.
Severity guidance: Medium — drivability or emissions affected, book it in this week
Symptoms you will notice
- Rough idle or stalling
- Lack of power
- Black smoke on diesels
- Hard starting when hot
Common causes
Ordered from most to least likely — start at the top.
- 1 EGR valve stuck open from carbon
- 2 Faulty EGR position sensor
- 3 Short in the signal circuit
- 4 Incorrect valve fitted after a repair
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Watch EGR actual vs commanded position at idle — a valve that should be closed but is not confirms the fault.
- ✓ Remove and inspect the valve for carbon holding it open.
- ✓ Check the position sensor signal sweeps smoothly across its range.
- ✓ Blank the passage briefly with a test plate to confirm the symptom disappears.
Repair options
- Clean or replace the EGR valve
- Clean the EGR passages in the manifold
- Repair the position sensor wiring
P0402 — frequently asked questions
Can I blank off the EGR? +
For off-road or test purposes only. On road vehicles it is illegal in most markets and will fail inspection.
Why does it stall at idle? +
Exhaust gas displaces oxygen in the intake; at idle the engine cannot tolerate the dilution.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.