P0406: EGR sensor A circuit high
The ECU is getting a voltage from EGR sensor A that is above the possible range. It is almost always wiring, a connector or the sensor itself.
| Code | P0406 |
|---|---|
| System | Engine and transmission |
| Group | P04xx, Emissions control |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0406 means
EGR sensor A reports to the ECU, usually on valve position or on the pressure or temperature of the recirculated gas; exactly what it measures is up to each manufacturer. The signal has gone above its normal range, which nearly always means an electrical rather than a mechanical problem.
Most common causes
- Loose or corroded sensor connector
- Broken or poor sensor earth
- Signal wire shorted to a positive supply
- Faulty EGR sensor
- Wiring fault back to the ECU
Symptoms
- Engine warning light on
- The ECU may switch off the EGR
- Slightly rough idle or a small loss of power
- Often no symptoms
Can you drive with P0406?
With care You can drive. The ECU usually puts the EGR into a safe mode, but the engine may run worse and fail an emissions test, so fix it soon.
How to check it
With the ignition on and engine off, check the EGR sensor value on your reader: a steady 5 volts or maximum reading points to a broken earth or an open sensor.
How to read and clear P0406 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0406 with this same explanation and whether it’s confirmed, pending or permanent.
With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.
Similar codes
- P0402 Exhaust gas recirculation (EGR) flow excessive
- P0403 EGR control circuit malfunction
- P0404 EGR circuit range or performance problem
- P0405 EGR sensor A circuit low
- P0407 EGR sensor B circuit low
- P0408 EGR sensor B circuit high
- P0409 EGR sensor A circuit malfunction
- P0410 Secondary air injection system malfunction
- P0400 Exhaust gas recirculation (EGR) flow malfunction
- P0401 Exhaust gas recirculation (EGR) flow insufficient
- P0411 Secondary air injection incorrect flow detected
- P0412 Secondary air switching valve A circuit malfunction
P0406 is a generic code, so it means the same on any make, for example on BMW, Ford, Mercedes-Benz, Peugeot, Renault, Volkswagen. See what Final OBD does on your car in makes and models.
What does code P0406 mean?
EGR sensor A reports to the ECU, usually on valve position or on the pressure or temperature of the recirculated gas; exactly what it measures is up to each manufacturer. The signal has gone above its normal range, which nearly always means an electrical rather than a mechanical problem.
Can you drive with P0406?
You can drive. The ECU usually puts the EGR into a safe mode, but the engine may run worse and fail an emissions test, so fix it soon.
How do you clear P0406?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0406 comes back.
Read it on your car
Final OBD reads the faults of every control unit for free, including each make’s own codes, and with Pro explains each one in plain English. Free clears engine faults at no cost.
Coming soon
Mid to late October 2026
If you want to try it in your car before anyone else, send us your email and we will add you as a tester.
info@finalobd.com