All codes › P0401

P0401 — EGR Flow Insufficient

P0401 is set when the ECM commands the EGR valve open during a drive-cycle monitor test and does not see the expected change in engine load, manifold absolute pressure, or DPFE/MAP-delta signal. The EGR system is supposed to flow a small amount of exhaust back into the intake under cruise conditions to reduce combustion temperature and NOx emissions — if no flow is detected, P0401 sets. The cause is almost always a clogged EGR passage, a stuck valve, or a failed flow-feedback sensor.

Pick your vehicle for a P0401 diagnosis

Select your exact year, make, and model below to get a diagnostic guide tuned to your vehicle's known failure patterns and TSBs.