P0407
EGR Sensor B Circuit Low
The signal from EGR position or pressure sensor B is below the lower diagnostic threshold. Indicates a short to ground, open signal wire or sensor fault.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- EGR sensor B internally faultyCommon
- Signal wire shorted to groundPossible
- Connector corrodedLess likely
Parts involved
- EGR Position Sensor
- EGR Pressure Sensor
- Sensor Wiring
P0407 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.