OBD code P0402

The ECU has detected too much recirculated exhaust gas entering the intake.

Estimated severity

Medium

Common symptoms

Rough idle
Power loss at low rpm
Black smoke or smoke during acceleration
Engine hesitates or stalls in some cases
Higher intake soot buildup over time

Likely causes

EGR valve stuck open from carbon buildup
Faulty EGR actuator or position sensor
Incorrect MAF or MAP reading
Vacuum or electric control fault
EGR cooler or passages clogged in a way that affects control

Recommended checks

1. Check commanded and actual EGR position with a scanner.
2. Inspect the EGR valve for sticking or heavy carbon buildup.
3. Check MAF/MAP readings because the ECU may infer EGR flow from them.
4. Inspect vacuum lines or electrical actuator connections.
5. Clean or replace the EGR only after confirming the control fault.

What does code P0402 mean?

P0402 means the EGR system is flowing more than expected. If too much exhaust gas enters the intake, combustion becomes unstable, the engine may lose power and smoke may increase. On diesel commercial vehicles, this may be caused by an EGR valve stuck open, control problems or incorrect pressure/air-mass readings.

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