This code usually needs a check soon to find out what is wrong.
Trouble codes · P0406
P0406 meaning
EGR Sensor A Circuit High
The same first verdict Car Assist shows from this code alone, before a diagnosis. The code does not tell the app whether the warning light is flashing.
What this code doesn’t tell you
A code says where the car noticed a problem. It does not prove which part failed, whether the fault is still present, or what repair this car needs. The engine, other codes, freeze frame and live readings matter.
Usual causes, most likely first
The order is a starting point across cars; the exact engine and its readings can change it.
- Open wire or a loose connector at the EGR sensor
- Faulty EGR position or pressure sensor
- EGR valve stuck with carbon
What you can check
With the engine off and cold, look from above for a loose connector at the EGR valve. Have the sensor signal tested before replacing the valve.
Words the car uses
- Stored codes
- Faults the car has confirmed and saved. They help explain a check-engine light, but a code alone does not prove which part needs replacing.
- Freeze frame
- A snapshot of the engine's readings when a fault was recorded. It helps show the conditions that caused the fault, even if the car now seems fine.
- Readiness monitors
- The car's own checks of its emissions systems. An unfinished check means the car has not tested that system yet, so a clean code scan may miss a fault.
- Exhaust recirculation (EGR)
- A system that sends some exhaust back into the engine to reduce emissions. Comparing requested and measured readings can help spot a stuck valve.
- Battery and ECU volts
- The electrical supply measured at the adapter or a car computer (ECU). Low readings can explain starting problems or unreliable diagnostic connections.
Find out what’s causing yours
Car Assist reads your car through an OBD-II adapter and your iPhone. Its assistant uses the codes, freeze frame and live readings to work through the likely cause with you.