P0402: EGR flow higher than the computer expects
Exhaust gas recirculation flow excessive detected
Severity: Monitor
P0402 means too much exhaust is being recirculated, which usually raises emissions rather than stopping the car, though a stuck-open valve can make the engine idle roughly.
It gets more serious if:
- Inspect soon: Have it inspected soon if the engine idles roughly, hesitates or stalls. TaT lists these as results of too much EGR flow.
P0402 in short
P0402 means the engine computer measured more exhaust gas recirculation flow than it expects. The usual cause is an EGR valve stuck open or dirty, followed by a sensor or intake fault. The car is usually driveable, but a rough idle or stalling means it should be checked soon.
The EGR valve lets a metered amount of exhaust back into the intake to lower combustion temperature. The computer sets P0402 when flow is above its calibrated amount, for instance when the valve should be closed.
A valve that sticks open is the simplest explanation, but the computer judges flow from other sensors such as airflow or manifold pressure, so a sensor fault can look the same.
On the Saab diesel service procedure, the test is to command the valve to 5% at idle and expect the airflow reading to stay above 14 g/s; if it does not, the valve is replaced.
Most likely causes
These are general causes for this code across vehicles. None is specific to one make or model.
Cause 1: EGR valve stuck open or not closing
Common general cause- Why it ranks here
- The Saab service procedure replaces the EGR valve when it fails the command test, and TaT lists a stuck-open valve first.
- What would change this
- Rises if the valve does not respond to scan-tool commands or idle is rough. Falls if the valve closes fully when commanded.
Cause 2: Airflow, pressure or EGR position sensor reading wrong
Possible — needs testing- Why it ranks here
- TaT names sensor malfunction and abnormal exhaust pressure as other possible causes; the computer infers flow from these sensors.
- What would change this
- Rises if the EGR commanded and actual values disagree with sensor data. Falls if sensors read sensibly and the valve fails its own test.
Cause 3: Intake or exhaust leak or blockage
Possible — needs testing- Why it ranks here
- The Saab procedure has you check the intake, exhaust, turbo and air filter for leaks or blockages before condemning the valve.
- What would change this
- Rises if a leak or blocked filter is found. Falls if intake and exhaust are sound.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all stored codes and freeze-frame data, and fix any other codes first.
IfOther EGR, airflow or boost codes are stored
It meansWork those first; they can set P0402 as a side effect.
Points to: Airflow, pressure or EGR position sensor reading wrong
IfP0402 is alone
It meansCheck the EGR valve.
Step 2: Command the EGR valve closed (around 5%) at idle and watch airflow or manifold pressure.
IfThe reading does not change as expected
It meansThe valve is not closing properly.
IfThe valve responds normally
It meansCheck for leaks, blockages and sensors.
Step 3: Inspect the intake, air filter and exhaust for leaks or blockage.
Warning:Keep hands and clothing away from the hot exhaust and moving belts when the engine is running.
IfA leak or blockage is found
It meansRepair it and retest.
IfNothing is found
It meansSuspect a sensor.
Points to: Airflow, pressure or EGR position sensor reading wrong
Symptoms
- Check engine light
- Uneven idle
- Hesitation or stalling Gets more serious: stop and have it checked.
How to fix
Step 1: With the engine off and cool, look at the vacuum hoses and wiring at the EGR valve for damage.
On your vehicle
We don't have reviewed vehicle-specific evidence for P0402 yet. The causes and tests above apply across vehicles.
Related codes
P0402 questions
What is the difference between P0401 and P0402?
P0401 means the EGR flow is lower than expected; P0402 means it is higher than expected, often from a valve that is stuck open.
Sources and review
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error