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.
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.
Related codes
Often seen with P0406
Read & clear P0406 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX