Diagnostic trouble code

P0401 EGR Flow Insufficient

The PCM commands EGR but does not see enough exhaust-gas flow.

EGR & Secondary Air Codes

Read This First

This code identifies the failed diagnostic test or circuit family. Confirm the basic checks before replacing parts, and keep freeze-frame data until the repair is verified.

Common Checks

  • Inspect EGR vacuum lines, EGR valve operation, and DPFE sensor hoses on equipped cars.
  • Check for clogged EGR passages.
  • Verify EGR command and feedback with a scan tool.

Common Repairs

  • Replace cracked DPFE hoses or repair EGR vacuum-control faults.
  • Clean restricted EGR passages.
  • Replace a failed EGR valve or feedback sensor after confirming the circuit.

Mustang Notes

Model-Year Applicability

Listed for 1996-2010 traditional gasoline Mustang pages in this first-pass catalog. Engine, calibration, and Ford-specific codes may narrow that range as more service data is added.

Sources

  1. SAE J2012DA Digital Annex of Diagnostic Trouble Code Definitions