What it means
The signal from EGR sensor B is below the expected range. The code identifies a low circuit signal; the sensor type and circuit layout vary by vehicle.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The EGR system routes some exhaust gas back into the intake to reduce combustion temperatures and emissions. The control module monitors the feedback signal from EGR sensor B, and sets P0407 when that signal falls below its expected range.
Common causes
Most likely first.
- EGR sensor B internally faulty
- Signal wire shorted to ground
- Connector corroded
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
How to diagnose it
- Use a scan tool to record freeze-frame data and compare EGR sensor B with other EGR readings to see when the low signal occurred.
- Inspect sensor B's connector and wiring for corrosion, loose pins, damaged insulation, or a wire touching ground.
- Check the sensor's live reading while commanding EGR operation, if the vehicle supports that test, and note whether sensor B responds.
- With the wiring diagram, check the sensor B reference, ground, and signal circuits for an unintended short to ground.
- Test EGR sensor B and its circuit against the manufacturer's specification to distinguish a failed sensor from a wiring fault.
Common fixes
- Clean and secure a corroded or loose sensor B connector.
- Repair a signal wire shorted to ground or other damaged wiring.
- Replace EGR sensor B if its output fails the manufacturer's specification.
Can I keep driving?
If the engine runs smoothly, a short, gentle drive may be possible, but avoid heavy acceleration or towing because reduced EGR feedback can contribute to knocking under load. Stop driving if knocking becomes pronounced or power loss makes the vehicle unsafe; continued operation can increase emissions and risk engine damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.