OBD codes / P0405
P0405
ModerateExhaust Gas Recirculation Sensor A Circuit Low
P0405 is usually safe to drive with in the short term. The main risks of ignoring it are pinging under load if the EGR system is disabled — which is hard on the engine over time — and a guaranteed emissions-test failure. Get it looked at soon, and sooner if you hear knocking or pinging when accelerating.
What this code means
P0405 means the sensor that reports the EGR valve's position is sending a lower voltage than the computer ever expects to see. The EGR system recirculates a small amount of exhaust back into the intake to cool combustion and cut NOx emissions, and the computer relies on this position sensor to know how far the valve is actually open. A constant low reading usually points to a failed position sensor, a wiring short to ground, or a bad connection rather than a mechanical EGR problem. On many engines the sensor is built into the EGR valve itself, so fixing it can mean replacing the whole valve. If the computer can't trust the position reading it may limit or disable EGR, which can cause light pinging under load and a failed emissions test. It's an electrical-circuit code, so checking the wiring and connector before buying parts is worthwhile.
Symptoms you might notice
- Check-engine light, often with little change in how the car drives
- Possible pinging or knocking under acceleration if EGR is disabled
- Rough idle or hesitation on some engines
- Failed emissions test
What it costs to fix
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0405 for my vehicle →Frequently asked
Can I drive with P0405?
Generally yes, for a while. The car will usually drive close to normal, but if the computer disables EGR you may get pinging under acceleration, which causes engine wear over time. Plan a repair soon rather than ignoring it.
Do I need a whole new EGR valve for P0405?
It depends on your engine. On many vehicles the position sensor is built into the EGR valve, so the valve gets replaced as a unit. On others the sensor is separate and cheap. A wiring or connector problem is also possible, so diagnose before buying parts.
What does the EGR position sensor actually do?
It tells the computer how far the EGR valve is open, so the computer can verify the valve is doing what it commanded. P0405 means that feedback signal is stuck low — the computer no longer trusts it, not necessarily that the valve itself is broken.
Will P0405 fail an emissions test?
Yes — in areas with OBD-based testing, an active check-engine light is typically an automatic fail, and EGR faults are emissions-related by definition. Fix the code and complete a few drive cycles before testing.
Seeing P0405 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0405 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.