P0406: the EGR position sensor signal is reading too high
EGR feeds a small amount of exhaust back into the engine to lower the temperature inside the cylinder and cut emissions, and a position sensor tells the engine control unit how far its valve is actually open. This code means the electrical signal from that sensor is reading higher than the range the computer will accept. With this signal out of range, the engine control unit can't trust what the valve is actually doing.
You might notice
- The engine warning light comes on
- The engine may idle unevenly or hesitate
- EGR
- — a system that feeds a little of the exhaust back into the engine to lower the temperature inside the cylinder and cut emissions
What the code itself says
P0406 is a powertrain (engine, gearbox and drive system) code, and the 0 after the letter means it is a generic code with a standard meaning.
Grouped here as: Engine running, fuelling and misfires — Air metering, fuelling, ignition, misfire, idle, boost, knock, oxygen sensors and the catalyst, all working together in the running engine. That grouping is ours, to help explain the code. The code's official family is the letter at the start.
This page is generic. Your car isn't.
A code on its own only tells you what the sensor saw, not what's actually wrong — and that changes next to your other codes. Read this one together with the rest of your scan and we'll work out what's really going on.
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