P0406

EGR Sensor A Circuit High

Auxiliary emissions (EGR) Generic OBD-II Medium

What it means

P0406 means the EGR position sensor's circuit is reading a high voltage — the ECM can't trust its report of how far the EGR valve is open. The engine usually drives normally, sometimes with a rough idle. It typically points to a failed sensor, a wiring short to voltage, or a corroded connector rather than the valve itself.

Medium

Can I keep driving? Yes — this is an EGR position-sensor circuit fault; the car generally drives normally, though you may get a rough idle. Fix it to pass emissions and keep EGR working correctly.

Real-world scan data

Seen in

1,844

scans in the past year

Found in

0.3%

of scans

0.5%

of scans that found faults

Appears alongside · share of P0406 scans

P0487in 43.8% of scans

C0487in 33.0% of scans

C0406in 30.4% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on (often the only symptom)
Occasional rough idle or hesitation
Slightly reduced fuel economy
Fails an emissions test

Common causes

Most likely first

Faulty EGR position sensorLikely
Wiring shorted to voltage or an open in the sensor circuitCommon
Corroded or loose sensor connectorCommon
Faulty ECM (rare)Less often

How to diagnose & fix

Work through it in order

Read freeze-frame data to confirm the high signal.
Inspect the EGR sensor connector and wiring for a short to voltage, an open, or corrosion.
Check the sensor's reference and signal voltages against spec.
Replace the EGR position sensor (or valve assembly, if integrated) if it tests faulty.
Clear the code and re-test.

FAQ

Quick answers

Is it safe to drive with P0406?+

Yes, generally. It's a sensor-signal fault, so drivability is usually normal aside from possible rough idle. Fix it so EGR operates correctly and you can pass emissions.

Can I just clear P0406?+

It returns unless the sensor or wiring is repaired. Clearing only tells you whether the fault is current or was intermittent.

Read & clear P0406 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX