P0402 fault code: excessive EGR flow
Plain-language definition
EGR A Flow Excessive Detected
What does it mean?
The EGR system sends part of the exhaust gas back to the intake side to lower the combustion temperature and reduce the formation of nitrogen oxides (NOx). The engine computer uses the EGR valve to set how much gas is sent back, depending on driving conditions.
P0402 means the engine computer has measured more EGR flow than it expected, or flow at a moment when there shouldn't be any. Depending on the engine, it tells this from the intake manifold pressure, the amount of fresh air measured by the air flow sensor (MAF), or a sensor in the EGR line. On engines with more than one EGR valve or circuit, the "A" in the code's definition tells which one is meant; the manufacturer decides which part it corresponds to.
Because too much exhaust gas disrupts combustion, there may be rough idling, shaking or even stalling. You may notice hesitation and a loss of power when accelerating; on diesel engines there may also be black smoke from the exhaust.
How serious is it?
It's rated Warning. Too much EGR flow disrupts combustion; symptoms such as stalling at idle or a loss of power can noticeably affect driving.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- EGR valve that can't close fully or stays open because of soot
- Problem in the vacuum or electrical circuit that controls the EGR valve
- EGR valve position sensor giving wrong information
- Inaccurate intake pressure sensor or air flow sensor (MAF)
- Fault in the EGR line's pressure sensor or its hoses (on some engines)
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Fiat
- EGR Drift positive air control - low air quantity, DC Offset
Related codes
How does it appear in the 2dakika report?
EGR A Flow Excessive Detected
If the code is read as a confirmed (stored) fault, the report shows it with the "Warning" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.