Code Definition

P0401 — Exhaust Gas Recirculation Flow Insufficient Detected

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0401

P0401 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0401 is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0401 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The ECM/PCM sets this code when it detects that the actual exhaust gas recirculation (EGR) flow is lower than the expected value. This can occur due to carbon buildup restricting EGR passages, a malfunctioning EGR valve, or a faulty sensor. Reduced EGR flow can lead to increased combustion temperatures and higher nitrogen oxide (NOx) emissions.

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