P0406
Exhaust Gas Recirculation Sensor "A" Circuit High
- Severity
- Medium
- Driving
- Drivable — book it in
EGR sensor "A" is reporting a voltage above the range the module accepts - typically shorted to voltage or an open earth. This sensor tells the module where the EGR valve actually is, or how much gas is actually flowing. Without a believable reading the module cannot verify what the valve is doing, so it disables EGR control. Sensor "A" is the manufacturer's designation, not a physical location; the vehicle's own documentation says which sensor that is.
Possible causes
- CommonWiring fault on the sensor "A" signal circuit
- CommonCorroded or water-ingressed connector at the sensor
- CommonFailed EGR position or pressure sensor
- PossibleSplit or blocked hoses to a differential pressure sensor
- PossibleLoss of the 5 volt reference or the sensor earth
- RareFaulty control module
What you might notice
- Check engine light on
- EGR system disabled
- Failed emissions test
- Rough idle in some cases
- Frequently no symptom the driver notices
What to check, in order
- Check the sensor connector for corrosion and water. This is the most common cause of both a stuck-high reading and an intermittent one.
- Measure the reference voltage at the sensor with the ignition on. If the reference is missing, the sensor is not at fault and the problem is upstream - and other sensors sharing that reference will usually have set codes too.
- Check for a good earth at the sensor. A lost earth commonly drives a signal high, which is why P0406 and P0408 are not always a shorted signal wire.
- Watch the sensor reading on the live data screen while the valve is commanded through its travel. A reading that never moves confirms a dead sensor or a dead circuit.
- On a differential pressure sensor, check its hoses. They perish, split and block with soot, and either fault produces an out-of-range reading from a perfectly good sensor.
- Look for other codes sharing the same reference or earth circuit before condemning this sensor.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Auxiliary emission controls
P0400P0401P0402P0403P0404P0405P0406P0407P0408P0409P0410P0411P0412P0413P0414P0415P0416P0417P0418P0419P0420P0421P0422P0423P0424P0425P0426P0427P0428P0429P0430P0431P0432P0433P0434P0435P0436P0437P0438P0439P0440P0441P0442P0443P0444P0445P0446P0447P0448P0449P0450P0451P0452P0453P0454P0455P0456P0457P0458P0459P0460P0461P0462P0463P0464P0465P0466P0467P0468P0469P0470P0471P0472P0473P0474P0475P0476P0477P0478P0479P0480P0481P0482P0483P0484P0485P0486P0487P0488P0489P0490P0491P0492P0493P0494P0495P0496P0497P0498P0499