P0407 Exhaust Gas Recirculation Sensor B Circuit Low

P0407 indicates a low input condition in Exhaust Gas Recirculation Sensor B circuit. The controller is seeing less EGR position or feedback voltage than expected from the B sensor path.

Code details

Generic OBD-II · P0

System: Emissions
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the EGR valve before confirming sensor B reference, ground, signal, and valve movement.

Symptoms of P0407

Check-engine light, often with no obvious change in how the car drives.
A failed emissions test or incomplete readiness monitors.
Sometimes a faint fuel-vapour smell (on EVAP codes).

Common causes of P0407

A worn catalytic converter or an oxygen/air-fuel sensor reading out of range.
EVAP leaks — a loose or failed gas cap, cracked hose, or purge/vent valve.
Exhaust leaks, fuel-trim problems, or a fault in a related monitor.

Useful checks before replacing parts

Compare EGR sensor B voltage, commanded EGR position, actual EGR feedback, MAP or MAF response, freeze-frame load, and related EGR circuit codes.
Inspect sensor B wiring, connector corrosion, reference voltage, ground, EGR valve movement, carbon buildup, and harness damage near heat sources.
Check whether the low signal is electrical, caused by a stuck EGR mechanism, or caused by missing reference or ground.

Related OBD-II codes

These nearby emissions entries can help compare wording and pin down the fault area.