2002 Yukon 2500 8.1 Reduced Power URGENT

Discussion in 'Engine & Drivetrain' started by camaro108, Jul 12, 2018.

  1. camaro108

    camaro108 TYF Newbie

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    Ncik
    Hi everyone,

    In the last last few months my 2002 2500 8.1 123k miles has been throwing itself into reduced power mode. Alternates between codes P1125 and P1221 (but mostly P1125), and never both together.

    Sometimes it will go a week without having an issue, it even went a month after I flushed the tranny, so I thought maybe that was somehow the issue. Now it's back and it is getting worse. I have to drive with my scanner plugged in to clear it. Sometimes it clears and stays away for days, sometimes it won't clear and comes right back until I shut the motor down and clear it. The situation is random. Happens while driving, while idling, while hot, while cold, while towing, and upon start up.

    What's werid is that it goes into reduced power mode and does its normal no revving above 1500, but sometimes the motor stalls while driving, and loses all brakes and power steering. The motor will not restart until I clear the code. It does one of three things when the reduced power mode kicks in:
    1. 10-15mph, reduced power
    2. Reduced power comes on, then engine stalls
    3. Reduced power comes on, it stays running, but runs rough

    I have replaced the APP sensor with a Delco part 3 times for giggles. New throttle body with sensors. New fuel pump. Checked all the relays and fuses. New plugs and wires. I have checked the entire wiring harness and pig tail connections on the sensors. I have checked ground wires. I even took it off roading for an hour last week thinking if it were a wire that it would act up.... It didn't. It was fine the whole way home, then had issues the next day.

    Since I use this thing to tow boats every day for my rental company, I need it running strong. It runs great and has never given me issues other than this. And obviously, it's potentially dangerous if the motor stalls and I have my 31 foot pontoon (10k lbs) on the back. I'm not stopping then for sure. Even just stopping the truck with no tow load when the engine dies is a scary instance.

    My mechanic that I've had for years and who I am friends with is also at his wits end. We cannot figure it out. The truck has been at the dealer for the last few days, they cannot "replicate the issue" when I know it's been sitting in their back lot for the last few days, unmoved. They're saying I need to replace the throttle body again with a dealer part, Which I know isn't the issue. They even said it might not be it... But good to try for $1300.

    What should I look for now guys? I know others have had this issue, but never follow up on what it was on the forums.
     
  2. about20ninj45

    about20ninj45 Full Access Member

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    What scanner do you have? Does it have the capability of logging or getting freeze frame data? It would be good to see if you are experiencing voltage drops to the tps, which will cause the vehicle to go into REP. I would also check resistance on the wires going to the Tps and the pedal to see if there is build up or corrosion or an break within the wire insulation.

    Another thing that causes is, if it sees more airflow at that required throttle position than its supposed to will put it in REP. Last and not least, if all else fails, have them reflash the pcm, which may be worth a shot. I experienced the same issues as you with my g3500 express 1 ton. Its scary when it happens and always be sure to ride in the far right lane, so when it goes into limp mode, you can pull to the side of the road.

    This is where having HPTuners, EFIlive and or a scan tool comes into play.
     
  3. camaro108

    camaro108 TYF Newbie

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    Thanks for the reply! I do have the live data option on my scanner, and I've checked that. Everything seems good as far as voltage and resistances go on the wires. The car has been in AZ its entire life, so corrosion is unlikely. I did check all the wires in the harness and the connectors, though.

    I might have them take a look at the Ecu even though they say there is nothing wrong with it.


     

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