P0402 - Exhaust Gas Recirculation Flow Excessive Detected
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0402 is an OBD-II generic code indicating that the Engine Control Unit (ECU) has detected an excessive amount of exhaust gas recirculation (EGR). This typically occurs when the EGR valve opens more than commanded or fails to close properly. The ECU monitors this via the Delta Pressure Feedback EGR (DPFE) sensor or by observing manifold absolute pressure (MAP) changes. Excessive EGR flow at idle or low load can cause combustion instability as the inert exhaust gases displace too much oxygen.
Possible Causes
EGR valve stuck open due to excessive carbon buildup
Faulty DPFE (Delta Pressure Feedback EGR) sensor or blocked/leaking sensor hoses
Defective EGR control solenoid vacuum supply keeping the valve open
Faulty MAP sensor or ECU software issue
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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