P0402 Error: EGR Flow Too High (Solution)

P0402 indicates an excessive exhaust gas recirculation flow, which is the opposite of P0401 (too low). The engine control unit detects that the air mass does not increase as expected when the EGR valve is closed, meaning that too much exhaust gas is being recirculated. The most common cause is a carbon-fouled EGR valve that is stuck open.


What does P0402 mean?
The EGR valve recirculates exhaust gases into the intake manifold. If it doesn't close completely or opens too much, too much exhaust gas is recirculated. The control unit detects this through a low air mass measurement or a lack of response when closing, and sets the P0402 code. This results in a rich combustion with soot formation.


Typical symptoms:
- Engine check light is on.
- Jerky movement, especially under partial load.
- Power loss
- Black smoke coming from the exhaust.
- Increased fuel consumption.


Most common causes:
- EGR valve is carbonized and stuck open (most common cause).
- Defective or incorrectly controlled AGR (Abgasrückführung) valve (N18).
- For EGR systems controlled by vacuum: Incorrect vacuum supply (vacuum is constantly applied).
- The mass airflow sensor is reporting insufficient airflow (e.g., due to a measurement error or a leak in the intake tract between the mass airflow sensor and the turbocharger).
- Clogged air filter.


Diagnosis with VCDS:
- Autoscan: P0402 code found in the engine control unit (01 - Engine).
- Perform actuator diagnosis for the EGR valve (N18).
- Check the air mass flow while the EGR valve is closed (it should increase).
- Remove the EGR valve and check it for carbon buildup and leaks.
- Check the vacuum supply to the AGR valve.