DTC P0401 Or P0402: EGR Flow - Insufficient/Excessive: Condition

DTC P0401 is set, when during deceleration, in which fuel cut is involved, difference in intake manifold absolute pressure value when EGR valve is opened, and when EGR valve is closed is less than specified value.

DTC P0402 is set, when during deceleration, in which fuel cut is involved, difference in intake manifold absolute pressure value when EGR valve is opened, and when EGR valve is closed is more than specified value. MIL is illuminated when ECM detects malfunction during 2 consecutive drive cycles.