P0406 code meaning
EGR Sensor A Circuit High
Powertrain system Generic code P04xx codes Check engine light
What P0406 means
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 gasoline 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.
P0406 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0406
- Check engine light on
- EGR switched off
- Diesel: possibly reduced power
- Otherwise hardly noticeable
Common causes of P0406
- Most 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
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EGR valve position sensorEGR valveSensor wiringEngine control module
What each part of P0406 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 06 | The exact fault in that area. |
What to do next
- Note P0406 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0406
What does P0406 mean?
P0406 means "EGR Sensor A Circuit High". Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. It is a generic code, so it means the same on every make.
Is it safe to drive with P0406?
Drive gently and only to a workshop. With P0406 the car can go into limp mode (reduced power) to protect itself.
Will P0406 fail an emissions test?
Yes, it can. P0406 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0406 to fix?
Difficulty: easy. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0406 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.