What it means
EGR flow is higher than expected when the valve should be closed, or higher than commanded when partially open. Typically a valve that has stuck open due to carbon, causing rough idle and stalling.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EGR valve should limit exhaust flow when closed and meter it when commanded open. P0402 sets when the module detects more EGR flow than expected, including flow while the valve should be closed; a valve that cannot seal can dilute the intake charge and make idle unstable.
Common causes
Most likely first.
- EGR valve stuck open
- Valve seat eroded — does not seal
Symptoms
- Check engine light on
- Rough idle
- Stalling, especially at idle
- Hesitation or reduced power
How to diagnose it
- Save freeze-frame data and review EGR command, position feedback, and available flow data to confirm the excess-flow condition occurs with the valve expected to be closed.
- At idle, observe whether the engine runs rough or stalls and compare the EGR position reading with the commanded closed state.
- Inspect the EGR valve and seat for carbon or damage that could hold the valve open or prevent sealing.
- Use an available scan-tool actuator test to command the valve closed and check whether position feedback and idle behavior respond.
- If the valve appears closed but excess flow remains, test the position or flow feedback system using the manufacturer's procedure.
Common fixes
- Remove carbon that is preventing the EGR valve from closing, if cleaning is appropriate for that valve.
- Replace an EGR valve that sticks open or fails to seal.
- Replace a valve with an eroded or damaged seat that allows flow when closed.
- Repair faulty position or flow feedback wiring if testing identifies it.
Can I keep driving?
If the engine stalls at idle, avoid stop-and-go driving and do not drive where a stall could put you in danger. Continued operation with excessive EGR flow can worsen rough running and hesitation.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.