Fault codeP0406

MODERATE

Exhaust Gas Recirculation Sensor A Circuit High

What this code means

Exhaust Gas Recirculation Sensor A Circuit High.

P0406 is a generic code: it means the same thing on every make. P0406 belongs to family P04xx — Emission controls. Its page explains how to read a code and groups all its codes by part.

Type of fault

The control unit reads a voltage on this circuit above its expected range. Usual causes: a broken wire or a poor ground, a short to a supply voltage, or the component itself. As with a low signal, check the wiring and connector before the part.

Exhaust gas recirculation (EGR) valve

The EGR valve sends part of the exhaust gas back into the intake to lower combustion temperature and nitrogen oxide emissions. The control unit opens it according to load and checks its position with a sensor built into the valve.

What you notice

Stuck open: rough idle, stalling, black smoke on diesels. Stuck closed: often nothing but higher emissions and sometimes pinging on petrol engines.

How to check it

Soot is the classic cause: a clogged or seized valve. Check its connector, then the valve itself and its pipes. In Klaro, compare the commanded EGR with the EGR error: a large and persistent error means the valve does not follow its command.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Commanded EGR
Actual EGR position, valve 1
EGR error
Intake manifold pressure

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
4Emission controls
06P0406