The 2021 Chevrolet Suburban's V8 engines (5.3L with AFM or 6.2L with DFM) can experience lifter collapse, often presenting with a distinctive tick and cylinder-specific misfire codes like P0302. This issue relates to the cylinder deactivation system's specialized hydraulic lifters.
Understanding AFM/DFM Lifter Collapse
Active Fuel Management (5.3L) and Dynamic Fuel Management (6.2L) use special lifters that can lock out to deactivate cylinders. These lifters have internal mechanisms more complex than standard hydraulic lifters, creating additional failure points.
When a lifter "collapses," its internal mechanism fails to maintain proper height. This creates excessive clearance between the camshaft lobe and valve train, causing the tick sound and preventing proper valve actuation. The affected cylinder may not fire correctly, triggering misfire codes.
P0302 and Lifter Connection
P0302 indicates cylinder 2 is misfiring. If the intake or exhaust lifter for cylinder 2 has collapsed, the associated valve won't open fully (or at all), causing incomplete combustion. The tick sound often accompanies the misfire code, making the diagnosis more apparent.
Symptoms of Lifter Collapse
The classic symptom is a pronounced ticking or tapping noise that follows engine RPM. The tick is often loudest on the affected bank and may be more noticeable when cold. As the lifter deteriorates, the tick may become constant.
Misfire symptoms include rough running, reduced power, and poor fuel economy. The check engine light illuminates with cylinder-specific codes. In severe cases, the engine may feel like it's only running on some cylinders.
Repair Options
Standard repair involves replacing the affected lifter(s). However, many shops recommend replacing all lifters on the affected bank or all 16 lifters to prevent repeat failures. The job requires significant disassembly: intake manifold, valve covers, rocker arms, and pushrods must be removed.
AFM/DFM delete is an alternative that replaces all cylinder deactivation lifters with standard lifters and uses an aftermarket tune to disable the feature. This eliminates the failure-prone components but affects fuel economy and may have warranty implications.
GM Coverage Programs
GM has issued technical service bulletins and special coverage programs for AFM/DFM lifter issues. Check with your dealer about applicable coverage. Many owners have received reduced-cost or no-cost repairs under these programs.