P0405
EGR Sensor A Circuit Low
Emissions / EGR
Generic OBD-II
Medium
What it means
P0405 means the EGR position sensor "A" signal is reading below its valid range — typically a short to ground or an open in the circuit. That sensor tells the ECM how far the EGR valve is open, so with a faulted signal the ECM can't verify EGR flow. The car usually still drives, but EGR problems can cause a rough idle and will fail emissions. The cause is generally the wiring or the sensor itself.
Medium
Can I keep driving? Yes — the car generally drives fine, though EGR faults can cause a rough idle or light hesitation; it will fail an emissions test until fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Rough idle or light hesitation in some cases
- Slightly reduced fuel economy
- Fails an emissions test
Common causes
Most likely first
- Signal wire shorted to ground or open in the EGR position-sensor circuit — most commonLikely
- Failed EGR position sensorCommon
- Corroded or loose connector at the EGR valve/sensorCommon
- Poor sensor ground or reference-voltage faultLess often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the EGR position signal is reading low/near zero.
- Inspect the EGR valve/sensor connector and wiring for damage, corrosion, or a short to ground.
- Check the sensor's reference voltage and ground against spec.
- Test the position sensor's output as the EGR valve moves; replace the sensor (or valve assembly) if it won't respond.
- Clear the code and drive a cycle to confirm the repair.
FAQ
Quick answers
Is it safe to drive with P0405?+
Yes, short term. The engine runs, though you may notice a rougher idle. Fix it to restore proper EGR operation and pass emissions.
Can I just clear P0405?+
It returns once the circuit reads low again. The sensor or its wiring needs repair.
Related codes
Often seen with P0405
Read & clear P0405 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