P0402 means the EGR system is flowing too much exhaust gas back into the intake manifold. The most common cause is an EGR valve stuck partially open, often due to carbon buildup on the valve seat. Diesel engines are especially vulnerable because of higher soot output.
P0402 means the EGR system is flowing too much exhaust gas back into the intake manifold. The most common cause is an EGR valve stuck partially open, often due to carbon buildup on the valve seat. Diesel engines are especially vulnerable because of higher soot output.
P0402 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0402 and illuminates the check engine light.
If your vehicle has triggered P0402, you may notice one or more of these symptoms:
Here are the most common causes of P0402, ranked by how likely they are to be the culprit:
Generally yes, for short-term driving. Driveable short-term, but excessive EGR flow causes rough idle, hesitation, and may stall the engine at low RPM. Extended driving with excess EGR contaminates the intake and accelerates carbon buildup on intake valves (especially direct-injection engines). Get it fixed before next emissions test.
Follow these steps to pinpoint the root cause of P0402:
Repair costs for P0402 vary depending on the root cause and your vehicle. Here are typical estimates:
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0402 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
These codes are often seen alongside P0402 or indicate related issues:
Short distances yes, but expect rough idle and possible stalling. Excessive EGR flow dumps soot and exhaust into the intake, which accelerates carbon buildup on intake valves, especially on direct-injection engines. Get it diagnosed within a few weeks.
No. EGR delete is illegal across the EU and UK. It increases NOx emissions, triggers a permanent check engine light, fails the periodic technical inspection (TÜV in Germany, ITV in Spain, TA in Lithuania, SKP in Poland), and can result in vehicle deregistration. Stick to cleaning or replacement.
Often yes. P0402 is usually caused by carbon stopping the valve from closing fully. Removing the valve, soaking it in EGR cleaner or carb cleaner, and clearing the seat resolves the code on roughly half of cases. If the solenoid or motor itself has failed, replacement is needed.
Diesel engines produce far more soot than petrol, so the EGR valve re-fouls quickly. If the EGR cooler is also blocked or leaking internally, the valve will stick open again within months. On heavily affected engines (BMW N47, M57), the cooler often needs replacement alongside the valve.
A 210,000 km imported diesel that looks too clean hides its faults in the OBD2 data. Here are the red flags a scan catches before you wire the money.
Clean a carboned diesel EGR valve yourself for €10-30. Symptoms, step-by-step removal, when to clean vs replace, and how to verify the fix with OBD2.
M57 vs M57N vs M57N2 across E60/E61. Swirl flap delete, twin-turbo wastegate on the 535d, ZF 6HP mechatronic. Five OBD2 checks before 3,000-12,000 EUR.
Connect any Bluetooth OBD2 adapter, scan for codes, and get AI-powered diagnostics with severity ratings and repair cost estimates.
Download Skanyx