P0402

P0402 is the opposite of P0401 — excessive EGR flow. The ECM commanded the valve toward closed (or completely closed during idle, where EGR should be zero) but is still seeing exhaust gas in the intake stream via MAP/MAF/DPFE signal. The dominant cause on gas engines past 80,000 miles is a carbon-coked pintle that won't seat fully closed: chunks of baked-on soot sit between the pintle and the seat, exhaust leaks past at idle, and the engine runs rough or stalls at stoplights with a P0402 stored. Diagnostic ladder: pull the valve, look at the seat under good light, and check for a visible gap or carbon flakes preventing seating; the pintle should snap closed under spring pressure with zero gap when uncommanded. Scan-tool EGR position live data at idle — a healthy valve reads pintle-closed (typically <0.7V on the position sensor); a stuck-partially-open valve reads 0.9-1.5V at idle and that's your code. Other common cause: a torn EGR valve diaphragm on older vacuum-operated valves (pre-2005 Toyota, GM, Chrysler) where intake vacuum pulls the valve open at idle when it should be closed — pinch the vacuum line at the valve and see if the rough idle clears. On DPFE-equipped Fords, a leaking DPFE rubber hose can over-report flow and trigger P0402 even with a perfectly sealing valve.

Vehicle-specific patterns: 2003-2010 GM 3.5/3.9L V6 (Impala, Malibu, Uplander, Lucerne) is the textbook P0402 — the linear EGR valve pintle cokes up with carbon and won't fully seat, idle goes rough, and the code throws within a few drive cycles; clean the seat with carb cleaner if the pintle isn't pitted, otherwise replace ($90-$160 part). 2000-2007 Chrysler/Dodge 3.3/3.8L V6 (Caravan, Town & Country) throws P0402 from a stuck EGR solenoid valve that won't fully close — common enough that aftermarket valves come with a TSB-style cleaning kit. 1998-2004 Toyota 4Runner/Tacoma with the 5VZ-FE 3.4L V6 throws P0402 from a torn EGR modulator diaphragm bleeding vacuum to the valve at idle — modulator is $40, valve is fine. 2005-2010 Ford Mustang 4.0L SOHC V6 throws P0402 from a stuck-open valve combined with a leaking DPFE hose — replace both the hose and the valve to clear it permanently. Estimated repair: $30 (carb cleaner DIY) to $300+ (valve + position sensor + gasket).