P0402 Generic (SAE)

Exhaust Gas Recirculation Flow Excessive Detected

Updated 2026-10-02 · Auxiliary emission controls

Severity

Medium

Typical repair cost

100 – 600 EUR

System

Powertrain

What it means

The ECU detected exhaust gas flowing into the intake when the EGR valve was commanded closed, or more flow than expected for a given command. It typically sees this as a MAF reading well below the model value at idle, an unexpectedly high MAP, or a DPFE voltage above the closed-valve baseline. The most common cause is a valve that will not seat because of carbon.

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Symptoms

Rough or unstable idle, idle speed dipping
Stalling after cold start or when coming to a stop
Hesitation and misfire-like stumble at low rpm
Black smoke and loss of power on diesels (lack of fresh air)
Check engine light, sometimes with P0300-series misfire codes

Common causes

EGR valve stuck open or not seating due to carbon on the pintle/seat
Failed EGR actuator motor or broken return spring
Faulty DPFE sensor reading high (Ford) or blocked DPFE hose
EGR vacuum solenoid stuck open or leaking
Wiring short to ground on the EGR control circuit
Faulty MAF sensor underreporting air mass

How to diagnose

At warm idle read EGR actual position: it should be 0-3 %. Compare MAF against the expected idle value for the engine (e.g. 2.0 TDI approx. 250-350 mg/stroke, 1.6 petrol approx. 2-4 g/s); a reading 30 % lower suggests the valve is leaking exhaust into the intake.
Command the valve closed with the scan tool and watch the idle; if it stays rough and smooths out when the EGR pipe is temporarily blanked off for the test, the valve is not sealing.
On vacuum-operated systems disconnect the vacuum hose at idle; if the idle improves, the solenoid is passing vacuum when it should not.
On Ford DPFE systems check the sensor voltage key-on engine-off: 0.9-1.1 V is normal; above 1.3 V indicates a faulty sensor or blocked hoses.
Remove the valve and check that the pintle returns fully onto its seat; clean or replace. Inspect the actuator gear train for wear on electric valves.
Check the EGR control circuit for a short to ground and verify the ECU driver duty cycle with a scope if the valve is electrically held open.

Frequently asked questions

Why does my engine stall with P0402?

Exhaust gas displaces fresh air at idle when the valve leaks, so the mixture becomes too inert to burn properly and the engine dies, especially when cold.

Can a dirty MAF cause P0402?

Yes. If the MAF underreports air flow the ECU calculates excessive EGR flow even with a healthy valve, so verify the MAF reading before replacing the EGR valve.

How long does the repair take?

Cleaning or replacing an accessible EGR valve takes 1-2 hours; on engines where the valve sits under the intake manifold allow 3-4 hours.