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P0401 means the EGR monitor detected insufficient flow

The monitor could not confirm the expected exhaust-gas recirculation flow under its test conditions.

September 25, 20261 min read
AI4Car quick readA short, original guide from the AI4Car knowledge library.

Check the system design, passages, valve command, and feedback. Carbon restriction is one possibility; verify flow and electrical control before replacing components.

Quick educational note

For information, not a diagnosis or repair instruction. Vehicle-specific checks are still required. Consult the manufacturer's guidance and a qualified technician.

How to use this information

This article explains general principles and does not establish what is wrong with your vehicle. Read the content limitations.

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P0401 means the EGR monitor detected insufficient flow | AI4Car