P0401Moderate severityEmissionsDIY: Moderate
P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient
The EGR system isn't moving enough exhaust back into the intake. Usually carbon buildup is clogging the EGR passages or the valve itself is stuck.
Can I keep driving?
Usually yes. Ignoring it can mean a rougher idle over time and an emissions failure.
Symptoms you might notice
- Check engine light
- Rough idle or an occasional stall at a stop
- Pinging or knocking under load on some engines
- Failed emissions test
What to check first
- Inspect the EGR valve and the passages leading to it. Heavy carbon buildup is the most common finding.
- On a scan tool, command the EGR valve open at idle. A healthy system makes the idle rough or stalls the engine, and nothing happening points to a stuck valve or blocked passages.
- If your system uses a pressure sensor (called a DPFE sensor on some Fords), check its hoses for cracks or soot blockage before replacing it.
- Clean or replace the valve and clear the passages once you know which part is at fault.
Most common causes
- Clogged EGR passages (carbon)
- Stuck or failed EGR valve
- Failed DPFE / EGR position sensor
Check it against your exact vehicle
A code means the same thing on every car, but where the parts are and what to check first depends on your year, make, model and engine. Tell CaliperAI what you are seeing and it will help narrow down the likely causes for your vehicle.
Related codes
Not sure this is your problem? Browse common car problems by symptom.
General information about this code, not a diagnosis of your specific vehicle. Safety-critical work such as brakes, fuel and airbags is best left to a qualified mechanic.