Active Fuel Management (AFM) lifter collapse in your 2017 GMC Sierra is a known issue affecting the 5.3L and 6.2L V8 engines. These specialized lifters can fail, causing concerning symptoms that require attention before engine damage occurs.
Understanding AFM Lifters
The AFM system uses specialized lifters on cylinders 1, 4, 6, and 7 that can lock and unlock to disable valve operation during cylinder deactivation. These lifters are more complex than standard hydraulic lifters and have demonstrated higher failure rates in GM's Gen V V8 engines.
Collapse Symptoms
A collapsed AFM lifter produces a distinct ticking or knocking noise, often loudest on cold startup. Check engine lights with misfire codes on AFM cylinders appear. Rough running during AFM activation occurs. The noise may diminish when the ECM disables AFM after detecting problems.
Why AFM Lifters Fail
The lifters contain a locking pin mechanism that can fail to engage or disengage properly. Oil supply issues, manufacturing defects, and repeated locking/unlocking cycles contribute to failure. Some production runs had higher failure rates than others.
Damage Progression
A collapsed lifter initially causes ticking and misfires. Continued operation can damage the camshaft lobe, creating a much more expensive repair. Early diagnosis limits damage to lifter replacement alone.