P0402
EGR A Flow Excessive Detected.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 4
- AreaAuxiliary emission controls
- 02
- FaultThe specific fault in that area
What it means
P0402 is the generic code for excessive exhaust gas recirculation (EGR) flow detected. The engine control unit saw more EGR flow than it expected, usually from a manifold pressure, EGR position or other feedback signal showing a change larger than the commanded EGR amount. This is often seen when the EGR valve is stuck open or leaking, and it is typically set when the valve should be closed or only slightly open, such as at idle or on deceleration.
Symptoms
- Engine warning light on
- Rough or unstable idle
- Stalling at idle or when coming to a stop
- Hesitation or poor response on light throttle
- Hard starting in some cases
- Slightly higher fuel consumption
Possible causes
- EGR valve stuck open or not seating fully because of carbon build-uplikely
- Faulty EGR valve actuator or internal position sensor giving wrong feedbacklikely
- Faulty EGR pressure or differential pressure sensor, or a blocked or split sensor hosepossible
- Wiring or connector fault in the EGR valve or sensor circuit (short, corrosion or chafing)possible
- Manifold absolute pressure sensor fault or vacuum leak affecting the reading the ECU uses to judge EGR flowpossible
- Faulty vacuum control solenoid or vacuum supply on vacuum-operated EGR systemspossible
- Outdated or faulty ECU software or calibration where a manufacturer bulletin lists it as a causerare
How to diagnose
- Read all stored and pending codes plus freeze frame data to see the engine load, speed and temperature when the fault set, and check for related MAP, MAF or EGR codes
- Visually inspect the EGR valve, wiring, connectors, vacuum hoses and sensor hoses for damage, corrosion, splits or loose fittings
- Check for vacuum or intake leaks that could upset the manifold pressure readings
- With a scan tool capable of live data, compare commanded and actual EGR position and watch the MAP or EGR pressure readings at idle with the valve commanded closed
- Run the EGR valve actuator test if available, noting whether it moves smoothly and fully closes, and whether idle quality changes as expected
- Remove the EGR valve if access allows and inspect it for carbon holding the valve open or preventing a clean seat
- Check the supply, ground and signal circuits of the valve and sensors against the manufacturer's wiring data for your model and engine
- Check for software updates or technical bulletins applicable to the vehicle and engine
How to fix
- Clean or replace the EGR valve if it is sticking open or not sealing, and clear any blocked passages as the manufacturer's procedure allows
- Replace a faulty EGR actuator or position sensor if the feedback does not match the commanded position
- Replace the EGR pressure sensor or renew blocked or damaged sensor hoses
- Repair damaged wiring or connectors in the EGR and sensor circuits
- Repair vacuum leaks or replace a faulty vacuum solenoid or MAP sensor if testing shows it is at fault
- Apply an ECU software update only where the manufacturer lists an outdated calibration as a known cause for this fault
Can I keep driving?
The car can usually be driven for a short time, but stalling or poor running can make it unsafe in traffic, so get it checked soon. Prolonged driving with a valve stuck open can worsen running quality and strain the engine management.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.