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OBD fault code guide

P0402 Code Meaning UK

P0402 means “Exhaust Gas Recirculation Flow Excessive Detected”. In plain English, the engine computer thinks too much exhaust gas is entering the intake through the EGR system. This can happen if the EGR valve sticks open, the control solenoid over-commands it, the position sensor reads incorrectly, or carbon build-up stops the valve closing properly.

📅 Updated June 2026 🇬🇧 UK diagnostic guide 🛠 EGR excessive flow fault
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Quick answer

What does P0402 mean?

P0402 means the ECU has detected too much EGR flow. The EGR system is designed to let a controlled amount of exhaust gas back into the intake to reduce emissions. If too much exhaust gas enters at the wrong time, the engine can idle roughly, hesitate, smoke, stall or feel flat because the air-fuel mixture and combustion quality are being upset.

Most likely area

EGR valve stuck open, EGR position sensor, solenoid, vacuum control, wiring, MAP/MAF readings or carbon deposits.

Urgency

Moderate to high if there is stalling, rough idle, smoke, limp mode or poor acceleration.

MOT risk

Can affect emissions, smoke output, engine warning light status and running quality.

Code meaning

P0402 — Exhaust Gas Recirculation Flow Excessive Detected

The full description is usually P0402 Exhaust Gas Recirculation Flow Excessive Detected. This means the ECU believes EGR flow is higher than it should be. It may detect this from MAP, MAF, EGR position, temperature or pressure changes depending on the vehicle.

This is different from P0401. P0401 means not enough EGR flow. P0402 means too much EGR flow. One points towards restriction or lack of flow; the other often points towards the valve being open when it should not be.

Mechanic view

Why excessive EGR flow causes rough running

An EGR valve stuck open can act almost like an internal exhaust leak into the intake. At idle and low speed, too much exhaust gas can dilute the fresh air charge, causing unstable combustion.

That is why P0402 can feel different from a blocked EGR fault. Instead of just poor emissions, you may get stalling, rough idle, hesitation and smoke because the engine is getting exhaust gas when it needs clean air.

Symptoms

Common symptoms of a P0402 code

P0402 often causes rough running symptoms because excessive EGR flow can disturb combustion, especially at idle and low speed.

Engine management light

A steady engine warning light is one of the most common signs of P0402.

Rough idle

The engine may idle unevenly if the EGR valve is open when it should be closed.

Stalling

Too much EGR at idle can make the engine stumble or cut out.

Hesitation

The car may hesitate or feel delayed when pulling away or accelerating.

Black smoke on diesel

Incorrect EGR flow can affect combustion and increase smoke on diesel vehicles.

Poor fuel economy

Wrong EGR flow can reduce efficiency and make the car use more fuel.

Common causes

What causes a P0402 fault code?

P0402 is usually caused by the EGR system flowing too much, or by sensor data making the ECU think flow is excessive.

Very common

EGR valve stuck open

Carbon or mechanical wear can stop the EGR valve closing properly.

Carbon issue

Carbon holding the valve open

Soot deposits can stop the valve seating cleanly, especially on diesel vehicles.

Sensor

Faulty EGR position sensor

The ECU may receive the wrong valve position signal and detect incorrect flow.

Control fault

Faulty EGR control solenoid

A solenoid or actuator fault can command too much EGR flow.

Vacuum system

Vacuum control problem

Vacuum-operated EGR systems can open incorrectly if control hoses or solenoids fail.

Airflow data

MAF or MAP sensor issue

Incorrect airflow or pressure readings can make EGR flow calculation inaccurate.

Wiring

EGR wiring or connector fault

Damaged wiring can affect valve command, feedback or sensor reference signals.

Previous repair

Wrong or poor-quality EGR valve

Incorrect aftermarket parts can cause repeat EGR flow codes.

ECU rare

Control strategy issue

Rare, but possible after valve, wiring, sensors and control systems have been checked.

Diagnosis

How a garage should diagnose P0402

✅ Scan all stored, pending and permanent codes.

✅ Record freeze frame data before clearing anything.

✅ Check whether P0402 appears with P0401, MAF, MAP, DPF or boost codes.

✅ Command the EGR valve open and closed with a diagnostic tool where possible.

✅ Check whether the valve closes fully at idle.

✅ Compare MAF and MAP readings when EGR is commanded.

✅ Inspect the EGR valve for carbon, sticking or poor seating.

✅ Check EGR position feedback, wiring and connector condition.

✅ Check vacuum hoses and solenoids on vacuum-operated systems.

Avoid this mistake

Do not clean blindly without checking movement

Cleaning an EGR valve may help if carbon is holding it open, but the valve must be checked for proper movement and seating. A valve that is electrically faulty or mechanically worn may still stick after cleaning.

The important question is not just “is it dirty?” It is “does it close fully when commanded?” If it cannot close, excessive EGR flow can continue.

EGR excessive flow checklist

Mechanic-style checks for P0402

A strong P0402 diagnosis should prove whether the EGR valve is physically stuck open, being commanded incorrectly, or being misread by the ECU.

Valve closed test

Check whether the EGR valve actually closes at idle and low load.

Command test

Use a scan tool to command EGR movement and watch engine response.

Position feedback

Compare commanded position with actual position where supported.

MAF reaction

MAF readings should change predictably when EGR is opened or closed.

Carbon inspection

Check for soot preventing the valve from seating correctly.

Sensor sanity check

Check MAP, MAF and temperature data before condemning the valve.

UK repair cost guide

How much does P0402 cost to fix in the UK?

Costs vary by vehicle, access, EGR design, diesel or petrol layout and whether the fault is cleaning, wiring, solenoid or valve replacement. These are rough UK guide prices only.

Diagnostic scan and live data test

Usually around £40–£120 depending on how much EGR command testing is included.

EGR cleaning

Can be moderate cost if access is simple, but cleaning is not guaranteed if the valve is worn.

EGR valve replacement

Can cost more depending on part quality, access and whether coding or adaptation is needed.

Vacuum or solenoid repair

Often cheaper than an EGR valve if a hose or control solenoid fault is found.

Wiring or connector repair

Costs vary depending on corrosion, access and whether the loom needs repair.

MAF/MAP sensor diagnosis

May be needed if the EGR flow calculation is being misled by sensor readings.

Safe driving advice

Can you drive with a P0402 code?

If the engine light is steady and the car drives normally, short careful driving may be possible. But if the car stalls, idles badly, smokes, hesitates, loses power or enters limp mode, get it checked quickly. Too much EGR flow can make the engine run poorly and increase emissions.

✅ Lower risk: steady engine light, no stalling, no smoke and normal performance.

⚠️ Medium risk: rough idle, hesitation, poor economy or repeated engine light.

🚫 High risk: stalling, heavy smoke, limp mode, severe hesitation, overheating or major power loss.

Real experience

What I would check first

On a real car with P0402, I would first check if the EGR valve is stuck open or being commanded open when it should not be. Rough idle that improves when EGR flow is blocked or reduced can be a strong clue.

I would also look at MAF and MAP readings. Sometimes the valve is blamed when the ECU is actually being misled by airflow or pressure data.

MOT implications

Will P0402 fail an MOT?

P0402 can lead to an MOT failure if the vehicle has an emissions-related engine warning light, excessive smoke, poor emissions, rough running or visible emissions system faults. Excessive EGR flow can upset combustion and make the engine run badly during the test.

Smoke risk

Incorrect EGR flow can contribute to diesel smoke and poor combustion.

Warning light issue

An engine warning light linked to emissions should be investigated before MOT.

Idle quality

Rough idle, stalling or hesitation should be repaired before presenting the vehicle.

Engine light MOT guide Common MOT failures
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Browse more OBD fault code guides

P0402 is one common EGR excessive flow diagnostic trouble code. For more common codes, meanings, symptoms, repair costs and MOT implications, use the main Motor Vehicle Expert fault-code hub.

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Frequently asked questions

Frequently Asked Questions About P0402

Find answers to common questions about P0402 EGR excessive flow faults, driving safety, repair costs and MOT implications.

What does P0402 mean?

P0402 means the engine computer has detected excessive exhaust gas recirculation flow. In simple terms, too much exhaust gas is entering the intake when the ECU does not expect it.

Can I drive with a P0402 code?

Short careful driving may be possible if the car runs normally and the engine light is steady. If the car stalls, idles badly, smokes, loses power, overheats or goes into limp mode, get it checked quickly.

Will P0402 fail an MOT?

P0402 can lead to an MOT failure if it causes an emissions-related engine warning light, excessive smoke, poor emissions, rough running or visible emissions system faults.

What causes a P0402 code?

Common causes include an EGR valve stuck open, faulty EGR position sensor, vacuum control fault, EGR solenoid issue, wiring fault, carbon deposits holding the valve open, MAP or MAF sensor issues, or incorrect EGR command from the control system.

How much does P0402 cost to fix in the UK?

A diagnostic check may cost around £40 to £120. EGR cleaning, wiring repair or solenoid repair may be moderate, while EGR valve, EGR cooler or intake cleaning work can cost more depending on access.

Is P0402 the same as P0401?

No. P0401 means insufficient EGR flow, while P0402 means excessive EGR flow. Both involve the EGR system but they point in opposite directions.

About this guide

Based on practical mechanic-style diagnostic experience

Motor Vehicle Expert publishes practical UK vehicle guidance based on real-world mechanical knowledge and hands-on diagnostic experience. This P0402 guide is written to help drivers understand EGR excessive flow faults before replacing expensive EGR parts unnecessarily.

Fault codes should always be treated as a starting point for diagnosis. If your car stalls, smokes heavily, runs badly, enters limp mode or has a flashing engine light, avoid continuing to drive and get professional help.