P0306 on RAM

The 5.7L HEMI engine with Multi-Displacement System (MDS) can experience premature lifter and camshaft wear. The MDS deactivation lifters are prone to failure, causing ticking, misfires, and in severe cases, camshaft lobe damage. This issue has led to class action lawsuits.

On 2003-2008 5.7L HEMI engines the cylinder-head valve-seat bores were machined without sufficient interference fit. Combined with localized coolant boiling and hot spots in the heads, an exhaust or intake valve seat can spin loose and drop into the combustion chamber. When the seat drops it is hammered by the valve and piston, causing a sudden misfire, loss of power, a heavy metallic knock, and in many cases destruction of the piston, valve and head. This is distinct from the well-known exhaust-manifold-bolt tick and the later MDS lifter/cam failure; it is a structural cylinder-head defect specific to pre-2009 (pre-Eagle) HEMIs. Overheating events dramatically raise the risk. The 2009 Eagle HEMI revision used improved seat material and tighter machining and largely eliminated the failure.

Early-production 2025 RAM 1500 trucks equipped with the new 3.0L Hurricane twin-turbocharged inline-six (Standard Output 420 hp and High Output 540 hp) are widely reported to throw check-engine lights and random/multi-cylinder misfire codes, often on cold start or under load in hot weather. Owners on the 5thGenRams and RamForum communities report P0300 (and per-cylinder P0301-P0306) within the first few thousand miles. Stellantis has issued multiple software TSBs (e.g., 08-055-25 for HO, 08-031-25 for SO, and a cold-start update) that reflash the ignition system control module (ISCM) and PCM; a separate TSB (09-025-25) addresses a purge-line/vacuum-leak source of lean misfires. This is a new-engine, new-generation problem outside the existing HEMI-focused coverage.

The 5.7L HEMI with Multi-Displacement System (MDS) in the 1500 Classic develops lifter failure, particularly on cylinders that deactivate. The roller lifters can collapse or seize, causing ticking noise and misfires. This is the same issue as the standard 1500.

The 5.7L Hemi V8 uses Multi-Displacement System (MDS) hydraulic lifters to deactivate four cylinders during light-load cruising. The MDS lifters are known to fail, causing a persistent ticking noise (the infamous "Hemi tick") and misfires on the deactivated cylinders. When an MDS lifter collapses or sticks, it cannot properly deactivate and reactivate the valve, leading to a dead cylinder. In severe cases, a failed lifter can damage the camshaft lobe, requiring a complete top-end rebuild.

Gas RAM 2500s with the 6.4L (392) HEMI V8 suffer a documented valvetrain defect in which the roller lifter needle bearings fail, the roller stops rolling and drags across the camshaft lobe, wiping out the lobe. The failure is linked to the truck's Multi-Displacement System (MDS/cylinder deactivation): when cylinders are deactivated, oil delivery to the affected lifters is restricted, starving the roller bearings. Owners report onset as a metallic 'HEMI tick' progressing to misfire, dropped cylinder and catastrophic top-end damage. A class-action lawsuit (Petro, et al. v. FCA US LLC, Case No. 1:22-cv-00621, whose named plaintiffs include a 2020 RAM 2500 owner) alleges FCA knew of the defect since at least 2012 and failed to disclose it. There is no safety recall, so repairs typically fall on the owner once warranty lapses.