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Confirm Lifter Failure

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Good Afternoon From Wisconsin,


Let me start by a providing a little backstory to this truck.  It is a 2008 GMC Sierra K1500 with about 150k on it (Vin J).  I was given this truck for free by my father in law with the assumption it had suffered a collapsed lifter due to AFM.  I am looking to get started on getting it functional again and decided to throw a battery in it and see what happened.  It started right up but feels like it's not running on at least a couple cylinders and has little to no power (pretty normal eh?) but it is also throwing just about every error known to man on the dashboard.  Air Bags, Brakes, Low Power, and a few others.  Now I'm wondering if either there is something more wrong with this truck, or possibly less?  Is it possible that a computer failure could throw all these codes and simultaneously keep it stuck in 4 cylinder mode, giving the illusion of AFM failure?  I would hate to tear the whole top end of the motor apart if it's not necesssary.  My thought is that I should take the valve cover off on the AFM side and check if the lifters are moving, and that if one or two aren't moving it would be a lifter failure, if none of them are moving it would be stuck in 4 cyl mode.  (If that's even possible).  Would this be the best way to verify this?


My apoloigies if this has been asked before.  I did extensive searching and couldn't find the answer to anything like this.  This is my first experience with AFM or GM Trucks that are this new so it's a whole new territory for me.  Thanks in advance!

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Clear all the codes before you do anything. If the truck lost communication to just about everything it can start throwing a bunch of codes for stuff. Use a scan tool to clear them and see what comes back when you start the key on or start the vehicle again.


The AFM/DoD has 2 cylinders on each bank that stop working when AFM is active. So you'd have to pull the valve cover on both sides to check for rocker movement. But before you even did that you'd want to use a scan tool to see why it's running rough. See what cylinder(s) aren't working and go from there. Cylinder 1, 4, 6 and 7 are AFM cylinders just a FYI.

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