P0406: Exhaust Gas Recirculation Sensor "A" Circuit High
P0406 means Exhaust Gas Recirculation Sensor "A" Circuit High. The EGR position/flow sensor signal is high. The signal voltage is higher than the maximum the module expects. Typical causes are an open ground circuit, a signal wire shorted to voltage, an unplugged connector, or a failed sensor.
Can I keep driving? Drivable with care. Diagnose soon: performance, economy or other components can be affected.
Common symptoms
- Check engine light on
- Possible rough idle or knocking
- Failed emissions test
Possible causes
- Faulty EGR valve or solenoid
- Wiring or connector fault
- Faulty EGR position sensor
- Engine computer driver fault (rare)
How to diagnose P0406
- Inspect the connector and wiring.
- Check power, ground and signal circuits.
- Command the valve on a scan tool and confirm it responds.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Related codes
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.