What does P0405 mean?
The exhaust gas recirculation (EGR) system feeds a small amount of exhaust back into the intake. That lowers combustion temperatures and cuts NOx emissions. This code means the computer found a problem with EGR flow or control.
The computer is seeing a signal voltage that is lower than the sensor should ever produce, so it is almost always an electrical problem rather than a mechanical one.
Codes are a starting point. They tell you which test failed, not which part to replace. Check for other stored codes and fix those in a sensible order.
Symptoms
- Check engine light
- Pinging under load (insufficient flow)
- Rough idle or stalling (excessive flow or stuck-open valve)
- Failed emissions test
Common causes
- Open in the 5 V reference wire
- Signal wire shorted to ground
- Unplugged or corroded connector
- Failed sensor
How to diagnose P0405
- With the key on, back-probe the connector: you should see about 5 V on the reference wire and a good ground (under 0.1 V drop).
- If reference and ground are good, check the signal wire for a short to ground with the connector unplugged.
- If the wiring checks out, the sensor itself is the likely fault.
- Command the EGR valve with a scan tool and watch the position feedback.
- Check passages for carbon buildup.
How to fix it
- Clean the EGR valve and passages
- Replace the EGR valve
- Replace the EGR sensor
- Repair vacuum lines or wiring
Estimated repair cost
Likely repairs for P0405 run from about $150 to $1,500, depending on the cause.
| Repair | Typical range (parts + labor) |
|---|---|
| Diagnostic fee (scan + testing) | $100 - $200 |
| EGR valve/passage cleaning | $150 - $600 |
| EGR valve replacement (gasoline) | $250 - $700 |
| EGR valve replacement (diesel) | $400 - $1,500 |
These are rough US estimates for an independent shop in 2026, based on typical parts prices and standard labor times. Dealers, big trucks, luxury brands and high-cost areas often run higher. They are not quotes. Use the repair cost estimator to adjust for your vehicle.
How serious is P0405?
Moderate severity
Usually drivable. Fix it to avoid pinging and failed emissions tests.
P0405 FAQ
What does P0405 mean?
P0405 stands for "Exhaust Gas Recirculation Sensor "A" Circuit Low". The exhaust gas recirculation (EGR) system feeds a small amount of exhaust back into the intake.
Can I drive with a P0405 code?
Usually drivable. Fix it to avoid pinging and failed emissions tests.
How much does it cost to fix P0405?
It depends on the cause. The likely repairs for P0405 range from about $150 to $1,500 at an independent shop in the US, plus a diagnostic fee of roughly $100-$200. These are rough estimates; dealer prices and some vehicles run higher.
What is the most common cause of P0405?
The most common causes are: open in the 5 V reference wire; signal wire shorted to ground; unplugged or corroded connector.