P0303 on RAM: How to Diagnose & Fix

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.

The 4.7L PowerTech V8 is intolerant of overheating and neglected coolant. Head gaskets leak combustion gases into the cooling system (air in coolant, coolant pushed from the overflow, steam/coolant smell from the exhaust on cold start). Once the aluminum heads warp or a corrosion channel opens between a water jacket and a cylinder, the machined-in valve seats can drop, causing catastrophic misfire and internal damage. A block/combustion-gas test in the coolant confirms it.

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.

Bulletin 09-011-25 describes cylinder-specific misfire codes, rough idle or valvetrain noise that may be related to worn intake camshaft high-lift lobes and/or intake rocker high-lift slider wear on specified upgraded 3.6L engines. It does not establish the older generic needle-bearing failure account for all Pentastar engines. 2019–2025 Ram 1500 DT built on or before November 14, 2024 with upgraded 3.6L ERC or ERG engines. Not the 5.7L HEMI, EcoDiesel or older 2013–2018 scope. This is an information-only bulletin, not a recall or authorization for repair.

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.

The 2.4L Tigershark uses MultiAir II electrohydraulic intake valve actuation: a solenoid-and-oil assembly (the "brick") bolted to the cylinder head replaces a conventional intake cam lobe profile. Its oil galleries and per-cylinder solenoids are extremely intolerant of dirty or degraded oil, and on a van that is already burning oil and running long fleet intervals the galleries varnish and the solenoids stick. The result is a cylinder-specific misfire, very rough idle, hesitation and a power-limiting limp mode. Because the same 2.4L ED6 MultiAir II unit is shared with the Jeep Renegade and Cherokee, the failure pattern and the repair procedure are identical across those vehicles. This is distinct from the transmission shift complaints already documented on this van - the driveability fault here originates in the cylinder head, not the 9-speed.

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.