Possible causes

– Exhaust Gas Recirculation (EGR) volume control valve stuck closed
– Faulty Exhaust Gas Recirculation (EGR) volume control solenoid valve
– Faulty EGR Valve
– Faulty EGR temperature sensor and circuit
– Exhaust Gas Recirculation (EGR) solenoid valve harness is open or shorted
– Exhaust Gas Recirculation (EGR) solenoid valve circuit poor electrical connection
– Dead (Weak) battery

Tech notes

EGR flow malfunction could be caused by a clogged EGR valve or EGR tube. Before replacing any parts try cleaning the EGR valve, tube and passages.

When is the code detected?

Exhaust Gas Recirculation (EGR) flow control is not responding

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Possible engine hesitation

P0400 HONDA Description

Early Exhaust Gas Recirculation (EGR) systems component s include and EGR Valve, and Engine Control