Powertrain, generic · Auxiliary emission controls
P0406 EGR Sensor A Circuit High
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible
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.
Likely causes
Sensor ground or return wire open
Signal wire shorted to 5 V or positive
Sensor in the EGR valve faulty
Moisture or corrosion in the connector
Symptoms
- Check engine light on
- EGR switched off
- Diesel: possibly reduced power
- Otherwise hardly noticeable
Repair estimate
DifficultyEasyDIY possible
Parts and labour€30–600
Time0.5–2.5 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
egr valve position sensoregr valvesensor wiringengine control module
Related codes
References: gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com, saabwisonline.com.