What to do about a P0406 fault code
P0406 rarely leaves you stranded, but left alone the EGR system runs without proper feedback and the light means an MOT fail. The code says the EGR position sensor's signal is too high, and we can test it where the vehicle is parked.
Can you keep using it with P0406?
Fine for now
Most vehicles run normally with P0406, so everyday use while you arrange a check is usually fine.
Get it booked this week
If the engine idles roughly, hesitates or the light keeps returning, book within the week before an MOT or a longer trip.
Stop and call us
Only if the vehicle goes into limp mode or stalls repeatedly. P0406 on its own seldom gets that far.
Signs that go with P0406
- The engine light with the vehicle feeling much the same
- An occasionally lumpy idle
- Other sensor codes if a shared supply is at fault
What P0406 means
The official definition is EGR sensor A circuit high. The sensor that reports the EGR valve's position is sending a voltage above its normal range, usually because of an open circuit, a short to the supply or a failed sensor inside the valve.
Common causes
A broken earth or signal wire
An open circuit on the sensor's earth can push the signal to the top of its range.
A short to the 5-volt supply
Chafed wires touching each other can hold the signal high.
A failed sensor inside the valve
On most engines the position sensor is part of the EGR valve, so a sensor failure means a new valve.
What to do right now
- Note any change in idle or pick-up, and whether other lights are on.
- Check the valve's plug is clipped in if you can reach it with the engine cold.
- Don't keep clearing it, as the stored data helps find intermittent faults.
- Book a check with the registration and full code.
How we sort P0406 where the vehicle is parked
We test the sensor's supply, earth and signal and watch its reading as the valve moves, for £100 + VAT. That shows whether a wire or the valve is at fault, and a garage carries out the repair using our findings. If your Ford Ranger is showing P0406 and has the locked SID212 ECU, software work on it costs £1,200 + VAT and is done off site, with a 7-day turnaround.
An EGR delete (£220 + VAT) is also available. If the vehicle can't be moved, say so when booking.
Reviews
Will P0406 put the car into limp mode?
It's uncommon, though some engines reduce power if they lose track of the EGR valve's position.
How long can I leave P0406 before it gets worse?
An electrical fault can stay the same for months, but corrosion and chafing usually get worse. Get it sorted before the next MOT.
Can P0406 damage the engine?
Not directly. Without position feedback, the ECU may shut the valve, which raises NOx but doesn't harm the engine.
Will my car pass its MOT with P0406 showing?
No, because the lit engine light is an MOT fail by itself.
Is P0406 something I can fix myself?
Checking the plug is fine. Tracing a short or open circuit needs a meter. If the signal reads low instead, you'll see P0405.
Is an EGR delete an option for P0406 on a road vehicle?
No, the delete is sold for off-road and export use only. Our EGR delete legality guide sets out the rules.
Get P0406 looked at where the vehicle is parked
Tell us where the vehicle is and what's on the dash, and we'll come and test the EGR sensor circuit.
More fault codes explained
Eccles, Manchester M30 0SF