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2004 yukon xl denali 6.0L P0420 code

Discussion in 'GM Powertrain' started by Pikey, Jun 5, 2013.

  1. Pikey

    Pikey Moderator Staff Member 2 Years ROTM Winner 1000 Posts

    My cousin contacted me and asked me about a p0420 code that he is getting on his truck. I read around and found that it could be a bad cat, a bad O2 sensor, a bad engine temp sensor, or a bad fuel pump. He tested the pump today and found the pressure to be 60psi while running, 52 psi when shut off, 44 psi 5 minutes after shut off, and 40 psi 10 minutes after shutoff. So, my question is, does this indicate a bad fuel regulator? Would a bad regulator cause the truck to run lean and therefor throw the code? or is basically a bad cat with that code? I also have a freeze frame from his scan tool that he sent me. Any ideas guys? He cleared the code and it came back a week later.

    DTC that caused the freeze frame PO420


    Throttle position 14.9%


    Engine RPM 546


    Load value 2.3%


    Air flow rate 6.89 GR/SEC


    MAP sensor 39KPA


    Coolant temp 201 F


    Short term fuel trim 1 3.1%


    Long term fuel trim 1 -4.6%


    Short term fuel trim 2 0.7%


    Long term fuel trim2 -4.9%


    Short term fuel trim 3 40.6%


    Long term fuel trim 3 99.2%


    Long term fuel trim 4 83.5%


    Short term fuel trim 4 65.6%


    Vehicle speed 0MPH


    Fuel system 1 Open 1


    Fuel system 2 Open 1








    I/M Monitors


    Misfire Mon ok


    Fuel sys mon ok


    Comp comp ok


    Catalyst mon oj


    HTD catalyst n/a


    EVAP sys mon inc


    SEC air sys n/a


    a/c refrig mon n/a


    oxy sensor mon ok


    oxy sen HTR ok


    EGR system mon n/a

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