Powertrain, generic · Auxiliary emission controls

P0402 EGR A Flow Excessive Detected

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. P0402 means too much exhaust is recirculated, or exhaust flows although the valve should be closed – CARB explicitly requires a leaking valve to be detected. Ford's DPFE check at idle with EGR off expects no pressure difference above the engine-off value; Ford diesels compare the measured EGR rate with the expected one, GM diesels the fresh-air deviation in the opposite direction. Petrol engines idle roughly or stall, diesels smoke and may lose power.

Likely causes

EGR valve stuck open, dirt under the seat
Ford: DPFE sensor drifting or hose wrong
Diesel: air leak between air mass meter and turbo, MAF drift
Valve control opens unintentionally

Symptoms

  • Check engine light on
  • Rough idle or stalling (petrol)
  • Jerking at part load
  • Diesel: black smoke, loss of power

Repair estimate

DifficultyMediumDIY possible
Parts and labour€100–800
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Check if the valve closes fully
  2. Inspect for carbon holding it open
  3. Check control signal

Parts involved

egr valveegr valve seatdpfe sensormaf sensor

Related codes

P0400P0401P0404P042EP0101

References: newtonnet.co.uk, fordservicecontent.com, gsi.ext.gm.com, saabwisonline.com.