Error code

OBD2 P0401

OBD2P0401
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Exhaust Gas Recirculation Flow Insufficient Detected.

Severity

moderateCan drive, but should address the issue to prevent long-term engine damage.

Summary

P0401 indicates insufficient flow in the Exhaust Gas Recirculation (EGR) system, which is typically located near the intake manifold.

Symptoms

  • Illuminated warning light
  • Increased fuel consumption
  • Knocking or pinging during acceleration
  • High nitrous oxide levels in exhaust

Common Causes

  • Defective EGR valve
  • Clogged EGR passages or valve
  • Faulty DPFE sensor (Ford applications)
  • Damaged wiring or connectors
  • Vacuum hose issues

Diagnosis

  1. Record all codes and freeze frame data.
  2. Inspect EGR valve type and control system.
  3. Check for visible damage in wiring or vacuum lines.
  4. Test resistance, ground integrity, continuity, and reference voltage of the EGR actuator and its signal circuit.

Fixes

  • Replace clogged or defective EGR valve— $250-$330
  • Inspect and repair vacuum control systems

FAQ

Is it safe to drive with P0401?

It is generally safe, but drivability issues may arise if the EGR system fails severely.

How difficult is it to fix P0401?

Diagnosing is straightforward, but fixing can vary from easy (replacing valve) to challenging (clearing passages).

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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