P0406EGR Sensor A Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. EGR sensor A is usually the valve position sensor; on Ford until about 2011 the DPFE differential pressure sensor. P0406 means its signal is above the upper limit – GM 2018 above 97.7 % of 5 V, GM 2005 above 94.7 % (both MIL after two trips), Ford petrol above 95 % for 4 s, Ford diesel above 4.70 V, Saab above 4.75 V. Typical is a signal wire shorted to positive or an open sensor ground, which GM names explicitly. EGR is then switched off.
- What you may notice
- Check engine light on
- EGR switched off
- Diesel: possibly reduced power
- Otherwise hardly noticeable
- Likely causes
- LikelySensor ground or return wire open
- PossibleSignal wire shorted to 5 V or positive
- PossibleSensor in the EGR valve faulty
- PossibleMoisture or corrosion in the connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.