P0405 Exhaust Gas Recirculation Sensor A Circuit Low

P0405 indicates a low input from EGR sensor A. The feedback signal for EGR position or flow is lower than expected.

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 checking the feedback circuit; a low signal can be wiring, ground, reference, or sensor related.

Symptoms of P0405

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 P0405

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

Check sensor reference voltage, signal wire, ground, connector condition, and terminal tension.
Compare EGR command with feedback data and watch for dropouts while moving the harness.
Inspect the EGR valve or feedback sensor for sticking, contamination, or mechanical position errors.

Related OBD-II codes

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