P0402: EGR Flow Excessive Detected
P0402 means the engine computer detected too much exhaust gas flowing back into the intake, usually because the EGR valve is stuck open or leaking. You can often drive short distances, but rough running, stalling or power loss can make it unreliable, so get it checked soon.
You can drive, but get it checked soon
The car may idle roughly, stall, jerk under part load, or on a diesel smoke and lose power, and limp mode (reduced power to protect the engine) is possible. Short trips are usually manageable, but stalling can be a safety risk in traffic.
What it means
The exhaust gas recirculation (EGR) system sends part of the exhaust back into the intake to lower combustion temperature and reduce nitrogen oxide (NOx) emissions. P0402 is set when the computer sees more recirculated exhaust than expected, or sees exhaust flowing when the valve should be closed. Emissions rules require the system to detect a leaking valve, which is why this code exists. On Ford vehicles, a DPFE sensor (a sensor that measures the pressure difference across the EGR flow) is checked at idle with EGR off, and the computer expects no difference above the engine-off value. Ford diesels compare the measured EGR rate with the expected one. GM diesels look at the fresh-air deviation in the opposite direction. The check engine light comes on, and the code needs a completed drive cycle (a set pattern of driving the computer uses to rerun its self-tests) to confirm a fix.
Likely causes
- EGR valve stuck open or dirt under the seatVery likely
Dirt keeps the valve from sealing, so exhaust keeps flowing when the valve should be closed.
- Ford: DPFE sensor drifting or hose connected wrongPossible
A drifting sensor or incorrect hose reports a pressure difference that looks like EGR flow.
- Diesel: air leak between air mass meter and turbo, or MAF driftPossible
Wrong fresh-air readings make the computer think EGR flow is too high.
- Valve control opens the valve unintentionallyLess likely
A fault in the control side can command or allow the valve to open when it should stay closed.
What you may notice
- Check engine light on
- Rough idle or stalling (gasoline engines)
- Jerking at part load
- Diesel: black smoke and loss of power
What to check, cheapest first
- 1Read the code and any related codes (P0400, P0401, P0404, P042E, P0101) and note freeze-frame data. · you can do it
- 2Look over vacuum hoses and, on a Ford, the DPFE sensor hoses for cracks, disconnections or incorrect routing. · you can do it
- 3On a diesel, inspect the intake piping between the air mass meter and the turbo for leaks or loose clamps. · you can do it
- 4Inspect the EGR valve for dirt under the seat or a valve that does not close, and clean or replace it as needed. · mechanic
- 5Check the DPFE sensor or air mass meter readings against expected values with a scan tool. · mechanic
- 6Clear the code and complete a drive cycle to confirm the fault does not return. · mechanic
Related codes
Frequently asked questions
Can I drive with P0402?+
Short distances are often possible, but stalling, rough running or power loss can occur. Have it checked soon.
Can a loose gas cap cause P0402?+
No. A gas cap affects the fuel vapor system. P0402 points to the EGR system, most often a valve stuck open.
Will P0402 pass an emissions test?+
Unlikely. The code is emissions-relevant and turns on the check engine light, which usually leads to a failed test until it is repaired.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10