P0405: EGR sensor A circuit low
The ECU is getting a voltage from EGR sensor A that is below the possible range. It is almost always wiring, a connector or the sensor itself.
| Code | P0405 |
|---|---|
| System | Engine and transmission |
| Group | P04xx, Emissions control |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0405 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 below its normal range, which nearly always means an electrical rather than a mechanical problem.
Most common causes
- Loose or corroded sensor connector
- Broken signal or supply wire
- Signal wire shorted to earth
- Faulty EGR sensor
- 5 volt reference supply pulled down by another shorted sensor
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 P0405?
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.
Open the bonnetthe in-depth explanation
How to check it
With the ignition on and engine off, check the EGR sensor value on your reader: a steady 0 or near 0 volts points to a broken wire or a short to earth.
How to read and clear P0405 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 P0405 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
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 an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P0401 Exhaust gas recirculation (EGR) flow insufficient
- P0402 Exhaust gas recirculation (EGR) flow excessive
- P0403 EGR control circuit malfunction
- P0404 EGR circuit range or performance problem
- P0406 EGR sensor A circuit high
- P0407 EGR sensor B circuit low
- P0408 EGR sensor B circuit high
- P0409 EGR sensor A circuit malfunction
- P0400 Exhaust gas recirculation (EGR) flow malfunction
- P0410 Secondary air injection system malfunction
- P0411 Secondary air injection incorrect flow detected
- P0412 Secondary air switching valve A circuit malfunction
To understand it properly
We explain how that system works, with drawings and no waffle, in our mechanics guide: EGR and particulate filter.
What does code P0405 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 below its normal range, which nearly always means an electrical rather than a mechanical problem.
Can you drive with P0405?
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 P0405?
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, P0405 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
