P0402 EGR A Flow Excessive Detected

Investigate soon

The ECU has logged a fault on P0402. The definition below is the exact wording the standard uses for this code.

Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.

The definition

P0402: EGR A Flow Excessive Detected.

P0402 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.

What to check first

Cheapest and fastest checks first:

Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
Check the connector at the part for corrosion, and that it is fully seated.
Clear the code and see whether it returns, and under what conditions.

What actually causes this on a VAG

This is the opposite complaint to a blocked EGR: the ECU reckons too much exhaust gas is getting into the inlet. On VAG engines that usually means the EGR valve isn't closing properly - commonly because soot has built up on the seat, or the valve is stuck part-open. Because exhaust gas displaces fresh air, the symptoms show up worst when the engine wants clean air: a rough or hunting idle, stalling as you come to a stop, hesitation when pulling away, smoke and poor cold running. It's worth sorting rather than living with, because a valve that won't shut keeps feeding soot into the inlet and, on a DPF car, into the filter.

Most likely causes, in order

EGR valve stuck part-open with carbon. The most likely cause by a distance, especially on diesels used for short trips. Remove the valve and look at the seat - if it won't close cleanly onto a clean face, that's your fault. Cleaning is often enough, provided the valve isn't worn or seized in its bore.
The valve is being held open by its control side. On vacuum systems, a control solenoid that has stuck, a hose routed wrong or a diaphragm that won't return can leave the valve commanded open. On electric valves, worn gearing or a jammed motor does the same. Watch commanded versus actual valve position in live data, or run an actuator test.
A leak letting exhaust gas past the closed valve. A distorted flange, a failed gasket at the valve, or a cracked pipe on the inlet side of the valve can let gas through whatever the valve itself is doing. Worth suspecting if the code returned soon after the valve was cleaned or refitted - a misplaced gasket or an unevenly tightened flange is easy to do.
A misleading airflow or pressure signal. Since the ECU calculates flow rather than measuring it, a faulty MAF or inlet pressure sensor can make a healthy system look like it's over-recirculating. Check those readings look sensible before condemning the EGR.

Worth knowing: Take the valve off and look before you order one - plenty of these are just carbon on the seat and clean up properly, though a valve that's worn or seized in its bore needs replacing. Don't be tempted by a blanking plate or an "EGR delete" either: it does nothing about the soot already in the inlet, the car no longer matches the emissions equipment it was built with, and a lit engine warning light is an MOT failure in its own right.

Reading the code is the easy part

A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.

VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.

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Common questions

What does P0402 mean?

P0402 means EGR A Flow Excessive Detected. It is logged when the ECU sees this circuit outside its expected operating window.

Can I drive with P0402?

The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.