What P0406 means
Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx.
How the engine computer detects it
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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- EGR switched off
- Diesel: possibly reduced power
- Otherwise hardly noticeable
Common causes
- Sensor ground or return wire open Most likely
- Signal wire shorted to 5 V or positive Possible
- Sensor in the EGR valve faulty Possible
- Moisture or corrosion in the connector Possible
How to diagnose P0406
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: egr valve position sensor, egr valve, sensor wiring, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Vehicles that report P0406 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Dodge Ram 1500 | 2005–2007 | 4 | 60k |
Counts of owner complaints to the NHTSA that mention P0406 (9 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- 06
- Specific fault
Questions drivers ask
Can I drive with code P0406?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P0406?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0406 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0406 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0406. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.