What does P0406 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 signal is reading higher than the sensor can normally produce, which points at a wiring fault or a dead sensor.
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 sensor ground wire
- Signal wire shorted to the 5 V reference or to battery voltage
- Water in the connector
- Failed sensor
How to diagnose P0406
- Check the sensor ground first: an open ground drives the signal high.
- Unplug the sensor: if the signal still reads high, look for a short to voltage in the harness.
- If the wiring is good, replace the sensor.
- 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 P0406 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 P0406?
Moderate severity
Usually drivable. Fix it to avoid pinging and failed emissions tests.
P0406 FAQ
What does P0406 mean?
P0406 stands for "Exhaust Gas Recirculation Sensor "A" Circuit High". The exhaust gas recirculation (EGR) system feeds a small amount of exhaust back into the intake.
Can I drive with a P0406 code?
Usually drivable. Fix it to avoid pinging and failed emissions tests.
How much does it cost to fix P0406?
It depends on the cause. The likely repairs for P0406 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 P0406?
The most common causes are: open sensor ground wire; signal wire shorted to the 5 V reference or to battery voltage; water in the connector.