P0401
Exhaust Gas Recirculation Flow Insufficient Detected
When the ECU commands EGR open, the actual flow measured by the DPFE sensor or the resulting MAP/MAF change is below threshold. By far the most common cause is a carboned-up EGR valve or blocked intake passages.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
What we see in the workshop
ON FORD ECOBOOST
Insufficient EGR flow is usually carbon blocking the passages rather than a failed valve. Cleaning the passages properly is the fix that lasts.
Common causes
Ordered by how often each turns out to be the cause.
- EGR valve clogged or stuck closedCommon
- Intake EGR passages blocked with carbonCommon
- Vacuum line to EGR (vacuum-actuated valves) crackedPossible
Parts involved
- EGR Valve
- EGR Passages
- Dpfe Sensor
P0401 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.