What P0401 means
Exhaust Gas Recirculation Flow Insufficient Detected
How to diagnose
- Read freeze frame data. When P0401 set, your ECU snapshotted every sensor at that moment. This tells you what the car was doing when the fault triggered — RPM, load, coolant temp, throttle position, fuel trims. Almost always enough info to figure out the cause without further testing.
- Check for related codes. If you have P0401 plus other codes, fix the earliest one in the chain first — a single root cause often triggers multiple codes.
- Cheap fixes first. For most codes, the order is: inspect connectors + wiring (free), check for vacuum leaks (cheap), replace sensor (moderate), replace mechanical part (expensive). Follow that ladder before dropping money on parts.
Manufacturer-specific descriptions
Different manufacturers use P0401 for slightly different failure modes:
| AUDI | Restriction in the EGR passages usually caused by carbon buildup, The EGR Valve is defective, Lack of proper vacuum or electrical signal to the EGR valve, Malfunctioning EGR Vacuum supply solenoid, Lack of proper EGR system feedback to the computer from the: Manifold Absolute Pressure Sensor (MAP), Differential EGR Pressure Feedback Sensor (DPFE), EGR Valve Position Sensor (EVP), EGR Temperature S... |
| BMW | Exhaust Gas Recirculation Flow Insufficient Detected |
| FIAT | EGR air control negative drift - high air quantity, |
| FORD | EGR Flow Insufficient Detected |
| HONDA | Exhaust Gas Recirculation (EGR) Insufficient Flow |
| MITSUBISHI | Exhaust Gas Recirculation Flow Insufficient Detected; EGR flow insufficient |
| NISSAN | Exhaust Gas Recirculation Flow Insufficient Detected |
| VOLKSWAGEN | Exhaust Gas Recirculation (EGR) Flow Insufficient |
Read P0401 on your own car
DIY Fix My Car reads P0401 plus 25,000+ other DTC codes with manufacturer-specific descriptions. Includes freeze frame data, likely fix parts, and AI mechanic chat. Download free.