P0401: not enough exhaust is being fed back into the engine
EGR feeds a small amount of exhaust back into the engine to lower the temperature inside the cylinder and cut emissions. This code means the engine control unit has asked for exhaust to flow back and measured less than it expects to see. It doesn't say why the flow is low, only that it is.
You might notice
- The engine warning light comes on
- You may notice a faint pinging sound from the engine under load
- 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
P0401 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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