1990-2025 Mazda MX-5 Miata Problems: 21 Known Issues

The NB Miata (1999-2005) crankshaft position sensor (CPS) is a known failure point. The sensor deteriorates from engine heat, causing intermittent stalling, no-start conditions, and random misfires. Failure is often heat-related - the car runs fine when cold but stalls or dies after reaching operating temperature.

Both the 1.6L B6 and 1.8L BP engines in the NA Miata use a timing belt that requires replacement every 60,000 miles. These engines are generally regarded as non-interference, so a broken belt usually strands the car without bending valves, but it stops the engine without warning. The water pump, driven by the timing belt, frequently leaks around the same interval and should be replaced proactively.

The earliest 1.6L B6 cars (all 1990 and 1991 up to VIN JM1NA...209446) use a 'short-nose' crankshaft. The crank pulley/timing sprocket is retained by a single bolt and a Woodruff key in a shallow keyway. Over time, and especially after a timing-belt/front-seal service where the pulley bolt and cam sprocket are removed and improperly reassembled (the key seated wrong, or the bolt not torqued to spec), the bolt loses clamp load. The pulley then walks on the crank snout, wallowing out the keyway and shearing the key. Left unaddressed this destroys the crankshaft nose. 1992+ cars and 1991 cars from VIN 209447 use a revised long-nose crank (identifiable by an 8-slot vs 4-slot pulley) and are not affected.

All generations of Miata (NA through NC) are prone to rear main seal leaks as the engine ages. Oil seeps from the crankshaft rear seal, dripping onto the clutch housing and eventually contaminating the clutch disc. High mileage engines and infrequent oil changes accelerate seal deterioration. This is a labor-intensive repair as the transmission must be removed.

The 1.6L B6 and 1.8L BP engines use hydraulic lash adjusters inside the bucket followers. Varnish and sludge from extended oil changes, or oil that is too thick or too thin, restrict flow into the adjuster so it cannot stay pumped up. The result is a persistent sewing-machine tick from the top of the engine, loudest on cold start and often not fully quiet once warm. It is frequently misdiagnosed by inexperienced buyers as rod knock, which is a deeper, lower-pitched noise from the bottom end.

On 1.8L BP engines, the Cam Angle Sensor (commonly called the CAS) mounts at the rear of the cylinder head, engaging the camshaft, and is sealed to the head by a single rubber O-ring. With age and heat cycling the O-ring hardens and shrinks, letting oil weep out of the back of the head. This is widely cited as the single most common oil-leak source on NA/NB Miatas; it typically fails before the valve-cover gasket. The oil runs down onto the nearby heater hoses (which it can rot) and the bellhousing. It is a nuisance leak rather than a failure, but a badly heat-soaked or oil-fouled CAS can also contribute to intermittent driveability faults.

2018-2019 MX-5 models are among 121,038 Mazdas recalled in November 2021 (NHTSA 21V875, Mazda campaign 5321K) for a defective Denso in-tank low-pressure fuel pump. Impellers manufactured with lower-than-specified density and exposed to production drying solvent for too long developed surface cracks and swelled, deforming enough to interfere with the pump body. The pump then binds or slows, starving the fuel supply. The car can crank without starting, run rough, illuminate the check engine light, or stall outright in traffic.

NHTSA recall campaign 00V032000 covered approximately 22,000 1999 MX-5 Miatas built November 1997 to November 1998. Insufficient clearance between the fuel filler pipe's non-return (check) valve case and shutter, combined with fuel-hose material properties, could cause the valve to stick. This produced a 'hard to refuel' condition and, in some cases, fuel spit-back at the nozzle during fill-up, a fire/burn hazard. Mazda dealers replaced the non-return valve with a modified valve free of charge, with owner notification beginning May 2000. On surviving cars the original service may or may not have been performed.

NA and NB Miatas are prone to structural rust in two well-known areas: the rear ends of the rocker panels (sills) and the front frame rails behind the front wheels. Road water enters through wheel-arch pinch welds and body seams and collects inside the double-layer sheet metal, rotting it from the inside out even when exterior paint looks fine. NB (1999+) frame rails are double-layer ('tinfoil sandwich') and rust worse than the single-layer NA rails. Salt-belt/winter cars are worst, but even garage-kept examples show rear-rocker rot. Because the rockers are structural on these unibody roadsters, advanced rot compromises chassis rigidity and safety.

The NC soft top channels water from the rain rail into two drains behind the seats that route down through the body and exit under the car. Pollen, leaves and acorns pack the drain screens, and the flexible exit tube frequently pops off its spigot inside the quarter panel. Once blocked, water backs up over the drain platform and pours behind the seats into the footwells and the trunk area. Owners often discover it only as soaked carpet, a musty smell, corroded floor-mounted electrical connectors, or standing water under the seats.

The externally mounted clutch slave cylinder on NA/NB/NC Miatas fails at the piston seal. Fluid weeps past the seal and collects behind the rubber boot, then the cylinder stops holding pressure and the pedal drops to the floor with no gear engagement - frequently without warning. Cars fitted with high-clamp aftermarket pressure plates fail sooner because of the higher pedal pressure, and owners repeatedly report cheap non-Mazda replacement cylinders lasting under a year. The ND uses a different, largely plastic-bodied slave (N251-41-920) that owners also criticize for durability.

The NC six-speed manual is widely reported to baulk and crunch on the 1-2 upshift when cold, and on many cars the second-gear synchro degrades until the grind persists warm. Contributing factors documented by owners are the factory gear oil's poor cold flow, a clutch release point that sits very high in the pedal travel so the clutch is not fully disengaged during a quick shift, and genuine brass synchro wear. A cold-only crunch is near-universal; grinding after the gearbox is warm indicates real synchro damage.

The 1994-2000 1.8L BP engines use a wasted-spark coil pack with an integrated igniter transistor. The early version (identified by the 4-pin input connector, later revised to 3-pin) is notorious for internal igniter/solder-joint failure, especially if the ignition is left in the ON position with the engine not running - the igniter transistor overheats and either burns out or melts its own solder connections. The result is a dead cylinder pair, a persistent misfire, and unburned fuel dumped into the catalytic converter.

The NA's retractable headlights are driven by two independent retractor motors, each containing a limit-switch assembly of three spring contacts riding on printed traces plus a set of diodes under a white plastic cover. Grease dries and the contacts and traces wear, so one light hunts up and down repeatedly before parking, stalls half-raised, or drops while driving. The shared 30A headlight relay and its fuse are the other common single point of failure, and a popped cap at the motor-to-linkage connection lets a lamp fall on its own.

The ND Miata's Mazda Connect infotainment system is plagued by USB connectivity drops, Bluetooth pairing failures, and occasional system freezes. USB-connected phones may disconnect repeatedly, and Bluetooth audio can cut out or develop significant delay. The 7-inch screen (8.8-inch on 2024+ models) can freeze requiring a system reset. Mazda has issued multiple software updates but the issues persist for many owners across model years.

Miata soft tops deteriorate over time from UV exposure, flexing during operation, and age. Vinyl tops develop cracks and tears, cloth tops fade and shrink. The rear plastic window (NA) or glass window (NB/NC/ND) can delaminate from the top material, causing water leaks and reduced visibility. Expected soft top life is 7-10 years with proper care.

NA and most early NB tops use a flexible plastic (vinyl) rear window, on many NA tops joined to the top with a zipper so the window can be lowered. With UV exposure and age the plastic yellows, hazes to near-opaque, and cracks (often starting at corners or the zipper seam); the zipper stitching tears out where the window meets the top. This is a near-universal age issue on unrestored cars and badly hurts rear visibility. A glass rear window with defroster was optional/standard on some later NB tops and does not haze, but zipper-window NA tops are the common case in this era.

NB Miata radiators are prone to failure at the plastic upper tank where it crimps onto the aluminum core. The plastic becomes brittle with age and heat cycling, developing hairline cracks that leak coolant under pressure. This can lead to sudden coolant loss and overheating, especially in spirited driving or hot weather. The OEM radiator typically fails between 80,000-120,000 miles.

Both the 1.6L B6 and 1.8L BP are belt-driven and Mazda specifies timing-belt replacement at 60,000 miles. On 25-35 year-old cars, belts frequently fail on age/dry-rot rather than mileage. The engines are non-interference, so a snapped belt will not bend valves, but it will strand the car. The water pump is driven behind the timing belt and commonly weeps or fails in the same 70k-170k window, so it is standard practice to replace the pump, tensioner, and seals while the belt is off since ~90% of the labor overlaps.

The NC Miata uses an electric power steering system that can fail due to a faulty steering angle sensor, EPS control module, or motor. When the system fails, the EPS warning light illuminates and power assist is lost, making the steering very heavy at low speeds. While the car remains drivable (it is manual rack-and-pinion underneath), parking and tight maneuvers become difficult.

The ND Miata (2016+) rear differential produces a noticeable whine or hum at highway speeds (50-70 mph) under light load. The noise is gear mesh related and varies with speed and throttle position. While not typically indicative of imminent failure, the noise is audible in the cabin due to the Miata's minimal sound insulation. More common on early ND production.