Diagnostic group

EGR & Secondary Air Codes

Exhaust-gas-recirculation and secondary-air monitor faults found mostly on older OBD-II Mustangs.

P0400-P0419

How to Use This Group

Start by reading all stored and pending codes together. A companion lean, misfire, EVAP, or oxygen-sensor code can change which test should come first.

Codes in This Group

P0401 EGR Flow Insufficient The PCM commands EGR but does not see enough exhaust-gas flow. P0402 EGR Flow Excessive The PCM sees more EGR flow than expected.

Sources

  1. SAE J2012DA Digital Annex of Diagnostic Trouble Code Definitions