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It seems this engine has multiple lobes on the camshafts that allow for more valve lift when more power is needed, and less when not needed when cruising or slowing down. The part that's failing isn't the rocker arm, but the oil control valve that allows the rocker arm to move between the multiple lobes. This valve has an electrical solenoid with 2 coil windings, that can fail. Also, GM has a TSB that warns of some pieces of the valve coming apart and falling into the camshaft area of the head. Ouch! So it's not a good idea to try and keep on driving.

I don't know, did GM discontinue the 2.5l after the 2015 model year? Or did they change to a different system of controlling the rocker arms?

GM shows the part #12633613 has been changed to #19419980, but none are available yet. A parts manager told a friend who has this problem that the government hasn't approved the change yet. With all the problems and changes going on with the EPA, this might take a long time. Hopefully this will lead to a recall, but what does someone do with their Impala or Malibu in the meantime? You know car dealers aren't going to allow much for a trade-in on a car that can hardly be driven.
 

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I did some more research, and found out the engine for 2014-15 was an LKW, which was upgraded from the previous LCV to include variable valve lift on the intake valves. The valve lift at low engine load was 4mm, and 10.5mm at higher engine loads. It looks like they went back to the LCV engine for 2016-19, which didn't have variable valve lift. Instead of fixing the badly designed system, they retro-fitted back to the old.
 
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