Diagnostic code
P0402 Code: Exhaust Gas Recirculation Flow Excessive
P0402 means the engine computer believes too much exhaust gas is entering the intake through the EGR system. An EGR valve stuck open, control fault, or misleading sensor feedback can make the engine stumble because exhaust dilutes the air-f
Educational reference only, not professional repair advice. A fault code is a starting point, not a diagnosis. Vehicle symptoms, live data, service history, and manufacturer-specific procedures change the repair path. If the check engine light is flashing, the vehicle is overheating, brakes or steering feel unsafe, fuel odor or smoke appears, or the engine is running poorly, stop driving when safe and get professional help.
Sources
Safety limits for this page
Use this page as a reference only. Do not perform hazardous repairs from a web guide. Stop when safe and contact a qualified mechanic if any warning condition below applies.
- Opening fuel lines, fuel tanks, or pressurized fuel components
- Flashing check engine light
- Overheating, smoke, or strong fuel smell
- Loss of power, severe shaking, unsafe braking, or unsafe steering
- Fuel odor, visible leak, smoke, or hard starting after refueling
- Burning smell, exhaust leak sound, or visible exhaust damage
Can I drive?
Avoid extended driving if the vehicle stalls, idles poorly, or loses power. Mild symptoms still need diagnosis soon.
Repair range
$80-$800
Scanner note
Basic OBD-II scanner with live data
Plain-English Meaning
P0402 means the engine computer believes too much exhaust gas is entering the intake through the EGR system. An EGR valve stuck open, control fault, or misleading sensor feedback can make the engine stumble because exhaust dilutes the air-fuel charge at the wrong time.
Common Causes
Common possibilities (most common first):
- EGR valve stuck open
- Faulty EGR control solenoid
- Carbon holding valve off its seat
- Incorrect EGR feedback sensor signal
- Vacuum routing fault on older systems
Order varies by make, model, mileage, and operating conditions. Do not replace parts based only on this list — verify with a scan tool and qualified mechanic.
Symptoms
- Rough idle
- Stalling at stops
- Hesitation
- Check engine light
Diagnostic Steps
- 1Check whether the EGR valve closes fully
- 2Inspect vacuum routing or electrical control
- 3Review EGR feedback sensor data
- 4Look for carbon preventing valve closure
- 5Retest idle quality after repair
Confusable And Related Codes
P0420
Compare →P0420 means the engine computer sees that the catalytic converter on bank 1 is not cleaning exhaust as efficiently as expected. The converter may be worn, but exhaust leaks, oxygen sensor problems, misfires, or fuel mixture issues can also
P0171
Compare →P0171 means the engine computer is adding extra fuel because bank 1 is running lean. In plain terms, the engine is getting too much air, not enough fuel, or incorrect sensor information. Vacuum leaks, intake leaks, fuel delivery issues, and
P0300
Compare →P0300 means the engine is misfiring randomly or across multiple cylinders instead of one clearly identified cylinder. Ignition, fuel, air leaks, compression problems, or timing issues can all interrupt combustion and trigger this code.
P0401
Compare →P0401 means the engine computer commanded EGR flow but did not see enough exhaust gas recirculation. Carbon buildup, valve problems, vacuum control faults, or sensor feedback issues can keep the system from flowing as expected.
FAQ
Can P0402 cause stalling?
Yes. Too much EGR at idle can dilute combustion and stall the engine.
Is P0402 the opposite of P0401?
They are related, but P0402 points to too much EGR flow while P0401 points to too little.
Can cleaning fix P0402?
Cleaning may help if carbon holds the valve open, but control and sensor faults must be ruled out.
This page is educational and is not a substitute for hands-on vehicle diagnosis.