P0303 on Jeep

HEMI-equipped Grand Cherokees can develop the characteristic MDS lifter tick. This ticking noise is most noticeable at idle and during light throttle. While often not immediately harmful, it indicates lifter wear from the MDS cylinder deactivation system.

FCA says a manufacturing issue on the 3.6L Pentastar Upgrade engine may cause wear at an intake camshaft high-lift lobe and/or an intake rocker-arm high-lift slider. The documented customer pattern is a cylinder-specific P0301-P0306 misfire with possible rough idle and valvetrain noise; FCA identifies 10,000-60,000 miles as the typical range. The bulletin covers 2018-2022 WK Grand Cherokee and 2021-2025 WL Grand Cherokee/Grand Cherokee L with ERC or ERG engines. WL vehicles are limited to those built on or before August 19, 2024 (MDH 0819XX). The previous card omitted the WK/WL split and build cutoff, described eTorque as the only engine, added P0300, and presented six separately purchased parts even though FCA provides complete side-specific service kits after diagnosis.

The 3.7L PowerTech V6 engine suffers from two common issues: cracked exhaust manifolds (causing ticking noise and exhaust leak) and valve cover gasket oil leaks. The cast iron exhaust manifolds develop stress cracks due to thermal cycling, with the passenger side being more common. TSB 09-001-10 addressed valve cover oil leaks. Head gasket failures have also been reported on higher-mileage engines.

The 3.6L Pentastar V6 used in JK (2012-2018) and JL (2018+) Wranglers suffers a documented valvetrain failure separate from the engine's oil-consumption problem. The needle roller bearings inside the rocker arms wear prematurely, loosen, and can drop out, shifting the rocker arm out of alignment so its roller stops turning and grinds against the camshaft lobe. This scrapes both parts and circulates metal debris through the oil. It typically begins as a persistent top-end 'Pentastar tick' (loudest at cold start, then constant) and progresses to random or cylinder-specific misfires, rough idle, bucking/surging, hesitation, power loss, and — if ignored — catastrophic cam/valvetrain damage. A proposed class-action lawsuit against FCA covering 2014-2020 3.6L Chrysler/Dodge/Jeep/RAM vehicles alleges a defective needle-bearing rocker design. Commonly surfaces after roughly 60,000-100,000 miles.

Early 3.6L Pentastar V6 Wranglers (especially 2012 and early-2013 builds) suffered a left (driver-side) cylinder head defect where the head would overheat and damage a valve seat/guide, causing low compression, a persistent ticking/tapping noise (often described as a 'left bank tick'), misfires, rough idle and reduced power. FCA acknowledged the defect and issued extended-warranty coverage (campaign X56) extending the head/related coverage to 10 years / 150,000 miles. A separate, related Pentastar tick on later builds is caused by failed rocker-arm needle bearings or collapsed valve lifters rather than the head casting. A class action was filed over the 3.6L tick. Left unaddressed, valvetrain wear can progress to major top-end engine damage.

The 4.0L inline-six heads carrying casting number 0331 (used on roughly 1999-2002 builds) were designed with enlarged intake/exhaust ports but left the deck wall between cylinders #3 and #4 too thin. Over high-mileage thermal cycling the head cracks in that area (visible through the oil-filler cap between the #3/#4 valve springs), often letting coolant weep into the combustion/oil galleries. It is one of the single most-searched TJ/LJ 4.0 failures.

The 4.0L coil-rail ignition system used on TJ Wranglers is known to develop internal failures that cause intermittent or persistent misfires. Owners report rough idle, hesitation, flashing check-engine lights, and cylinder-specific misfire codes, often after moisture intrusion, age, or heat exposure. Because the rail serves all cylinders, diagnosis can be less straightforward than on engines with individual plug wires.