Trouble codes › P0400
P0400 Exhaust Gas Recirculation "A" Flow
Emissions
P0400 means the EGR system isn't flowing exhaust back into the intake as expected, often from carbon buildup.
The engine computer found a general problem with EGR flow: the exhaust it recirculates into the intake isn't behaving as expected (too little, too much or no measurable change).
Usually drivable, but watch for pinging under load or rough idle. Get it checked soon.
Common causes
- Carbon-clogged EGR passages or valve
- A sticking or failed EGR valve
- A vacuum or electrical problem with the EGR control
- A faulty EGR position or pressure sensor
Symptoms
- Check-engine light
- Pinging under load, or rough idle and stalling if stuck open
- Failed emissions test
What to check first
- Check vacuum hoses and wiring to the EGR valve.
- Remove and inspect the valve and passages for carbon.
- Command the valve with a scan tool (electronic valves) and watch idle change.
- Look for service bulletins for your engine.
What does P0400 mean on your vehicle?
The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.
Ask iRepair about P0400No scanner? Most auto parts stores read check-engine codes for free.
Related codes
General guidance for P0400 on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.