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  1. 911 Problems Forum
    i have an 2006 duramax and i have been throwing an unknown code po 401 according to my bullydog. any help with this code number
  2. 911 Problems Forum
    My 05 ( with 4" exh, chip, intake ) is throwing P0401 =EGR flow insufficient and P0404= EGR control circuit performance. Do I need to worry about these codes? Will it effect my truck negatively? Can I run with them on?