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  1. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    The big fluctuation is when I started it
  2. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Sorry didn’t mean to double send that. But I will check that too as soon as I have more than 5 minutes to troubleshoot. L terminal circuit is what plugs into alternator from ecm correct?
  3. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    I will. Wife had to run errand and I’m watching the kids. I also noticed when I tried to graph the battery it didn’t show anything. Just blank. When I try component testing it says module not supported
  4. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    I will go back out there and do that soon my wife had to leave for a moment so watching my kids. But I also noticed when I tried to graph the battery it’s just blank with no readings. When I go to component testing to try to control certain components it says module not supported or something...
  5. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

  6. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Yeah I’ve seen it as high as 15.5
  7. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Only grounds I’ve changed are neg terminals at battery to front of frame and front of engine. Also ground strap rear driver side. I will check those grounds. Also yes this is idle no pressure on accelerator. And also, battery voltage showed around 15.1 doesn’t jump too much around .25 at when I...
  8. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Tested fuses all good. Took power off alternator with key on, still did it. Going to take battery and alternator to get tested. Also started it and with idle going up and down I did a graph of acc sensors and tps. Seems off to me but I’ve never done this kind of testing on a vehicle with so many...
  9. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Sorry for the late replies, I have been busy at work. I work 12 hr shifts so it’s hard to do any diag work after work but I finish up today and will do more testing. I’m going to take the battery and alternator to autozone to have them test tomorrow. Also going to go through my relays and...
  10. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    *** start not charge im doing this diag when I finish work Wednesday
  11. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Yes the other codes are for voltage issues at a bunch of sensors. So I’m starting to think the alternators internal regulator is overcharging? To test that I would need to charge it and keep multimeter on battery to see voltage spikes or drops?
  12. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    I checked voltage at battery, alternator, and starter last night. All 12.55
  13. S

    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Yes Yes, thank you very much. I replace with all OEM parts. Alternator is AC Delco, along with all the other parts I mentioned. I am getting positive terminals in the mail from rockauto Wednesday. I’m going to try and run more tests. All terminals have been cleaned and seem fine but I’m not as...
  14. S

    2009 Yukon XL doing some weird idle and electrical things

    I have an 11 with this code that only comes on with key on engine off. According to this doesn’t it mean it should only come on when engine is running? I’m at a loss on what to check next. If I start it it runs find with no codes. But if I just turn the key on voltage drops rapidly and light...
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    11 Yukon XL Denali Electrical Issue P0621 SOLVED

    Hello, new to the group but long time stalker. I bought this Yukon a few months ago and after a month had a shop AFM delete it. Now I’m having some kind of electrical issue. I have a ton of pending codes but one consistent P0621. Most of the codes pending seem electrical. Is it possible my ECM...
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