Exhaust Gas Recirculation Flow Excessive Detected
What does P0402 mean?
The P0402 code means the vehicle's onboard diagnostic system has detected: Exhaust Gas Recirculation Flow Excessive Detected. This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Rough or unstable idle
- Engine surging or hesitation
- Engine stalling at idle
- Pinging or knocking under load
Probable Causes (Ranked by Likelihood)
- EGR valve stuck open Very High
- Carbon buildup holding EGR valve open High
- Faulty EGR pressure feedback sensor (DPFE) Moderate
- Blocked EGR passages causing incorrect readings Low
Step-by-Step Diagnostic Procedure
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Visually inspect the EGR valve for carbon buildup preventing full closure
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With the engine idling, manually close the EGR valve -- if idle smooths out, the valve is stuck open
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Test the DPFE sensor by comparing its voltage readings to specifications (typically 0.45V at idle)
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Check EGR vacuum lines and electrical connectors for damage or leaks
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Clean the EGR valve and passages with carburetor cleaner and retest
Frequently Asked Questions
Can I drive with code P0402?
You can drive short distances, but the engine may idle rough or stall. Excessive EGR flow dilutes the air-fuel mixture at idle, causing drivability problems. Repair promptly to avoid stalling in traffic.
Can I clean the EGR valve instead of replacing it?
Yes. Many EGR valves can be removed and cleaned with carburetor cleaner to remove carbon deposits. If the valve moves freely after cleaning and holds vacuum, it may not need replacement.
Why is P0402 especially common on Ford vehicles?
Ford vehicles with DPFE (Differential Pressure Feedback EGR) sensors are prone to this code. The DPFE sensor fails frequently and gives false high-flow readings, triggering P0402.