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Thread: LML Reduced Engine Power Keeps leaving me stranded

  1. #1
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    Default LML Reduced Engine Power Keeps leaving me stranded

    Good morning. This is my first post on EFI (sorry it's a long one), and I see that many of you have lots of knowledge and I hope someone can help me out of this predicament. I have taken the truck to several local dealerships but they won't even touch it due to the DPF delete.

    As soon as I got my 2011 a couple years ago I did the DPF delete and an eBay autoCAL. It was problem free until last year out of the blue it would go into reduced engine power mode and completely cut all power and reduce engine RPM to approximately 1000 RPM. It will not even go up a hill. Sometimes it would be provoked by jumping on the throttle, other times it would do it while I was cruising down the interstate. Once it was fine when I shut off the truck and then the next time I started it, it was in REP. So there does not seem to be any rhyme or reason with the cause and effect.

    Maybe there is a simple solution to get it out of REP, but I cannot find a rhyme or reason for that either. When I'm on the side of the road after it has tripped, sometimes I can get it to reset easily with a few cycles of the ignition, other times it has taken me an hour of sitting and waiting and trying various key cycles to get it out of REP. I have even tried re-flashing with different tunes, but that does not take it out of REP. The other day it went into REP when I got heavy on the throttle on the interstate, before I lost all my speed, I popped it in neutral and cycled ignition off and then cranked it again and it cleared.

    The problem has been dormant for nearly a year, but in the past month it has started doing it again and now my family and I are on vacation in the mountains and it has done it a number of times and I'm worried it'll do it on one of these bad switch-back roads where there is no shoulder to pull over on.

    I have used the autoCAL to search for/clear any codes, but it never displays any and the CEL never comes on.

    If anyone can point me in the right direction it would be much appreciated.
    '11 CCSB Denali HD LML Stock other than DPF delete and EFI.

    '91Foxbody turbo LS w/powerglide 8.63 @158mph

  2. #2
    Lifetime Member Tre-Cool's Avatar
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    sounds to me like something could be loose wiring wise. I've had similar situations where the tcm plug has not been tightened or installed properly and this causes a similar situation due to a loss of comm's. Maybe check any wiring into your transmission etc as a first check?

  3. #3
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    Ok will do. Thanks for the guidance.
    '11 CCSB Denali HD LML Stock other than DPF delete and EFI.

    '91Foxbody turbo LS w/powerglide 8.63 @158mph

  4. #4
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    I think that you need to get a scan tool that you can access all of the systems check everything for codes and data that just doesn't look right. I've seen simple break light switch or steering angle sensor do the same thing. Generally the oem uses rep to protect you from what it's data thinks to be a dangerous situation. Just think of it from a different point of view. Good luck

    Sent from my SM-G930V using Tapatalk

  5. #5
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    Thanks for the reply, but I just got this issue fixed last month...thankfully since the issue began over a year ago. Luckily I gained a friend who is a technician at the local Chevy dealer, and as you recommended, he hooked up the fancy scanner and immediately told me the accelerator pedal position sensor assembly was the problem. Sure enough, I replaced the accelerator assembly and have been problem free since!
    '11 CCSB Denali HD LML Stock other than DPF delete and EFI.

    '91Foxbody turbo LS w/powerglide 8.63 @158mph

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