Exhaust Gas Recirculation Flow Excessive Detected
The EGR system is allowing too much exhaust gas back into the intake.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The EGR (Exhaust Gas Recirculation) system is designed to reduce emissions by recirculating some exhaust back into the engine to lower combustion temperatures. If the EGR is leaking or stuck open, too much exhaust gas enters the intake, which causes performance issues.
What the computer is actually seeing
The engine control module (ECM) monitors the EGR flow through various sensors. If the flow indicated by the EGR and the expected values determined by the ECM don't match, it triggers the P0402 code, meaning too much exhaust gas is coming back into the engine.
What a healthy reading looks like
Typically, the EGR flow should be between 5-15% at idle; anything higher could trigger the P0402 code.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Inspect all EGR system hoses and connections for leaks or damage. Fix or replace as needed. Decision: If leaks found, repair them. If not, move to step 2.
- 22. Check the EGR valve for proper operation. With the engine running, use a scan tool to command the EGR valve to open. Observe the change in RPM. Decision: If the RPM drops significantly, the EGR is functioning. If no change, replace the EGR valve.
- 33. Inspect EGR passages for carbon buildup or blockages. Clean out any obstructions you find. Decision: If passages are clogged, clean them. If they are clear, move to step 4.
- 44. Check the sensor(s) that report EGR flow to the ECM. Measure the voltage or resistance as specified. Decision: If outside manufacturer specs, replace the sensor.
Common causes
- Faulty EGR valve
- Clogged EGR passages
- Vacuum leaks in the EGR system
- Faulty sensors monitoring EGR flow
- ECM software issues
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with a P0402 code?
It's drivable, but reduce your speed and avoid heavy loads. It can affect emissions and engine performance.
Will the P0402 code come back after clearing it?
If the underlying issue isn't fixed, it will come back after a few drive cycles.
Why does P0402 sometimes pair with P0401?
P0401 indicates insufficient EGR flow, while P0402 indicates excessive flow; both can occur if the EGR system has issues.
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