2021 Mazda 5: What to check before buying

Oil disappears between changes with no visible leak. The low oil light usually comes on 2,000 to 5,000 miles after a service, often on cars with under 20,000 miles, and some engines use up to a quart every 1,000 miles. Dealers typically confirm there is no leak, top off the oil, and offer no lasting fix. Several owners cite a service bulletin that blames faulty valve stem seals. Owners worry that the steady oil loss will lead to early engine damage.

Rear differential failure is the most serious pattern. Owners hear a new noise or a sudden loud bang. After that, the cracked housing locks the rear wheels whenever all-wheel drive engages, which creates a real loss-of-control risk. Failures are reported before 26,000 miles. Oil consumption also shows up here, with low oil warnings 3,000 to 4,500 miles after a change. Other reports cover leaking seals and timing cover gaskets, radiator leaks with coolant loss, overheating, jerky driving below 30 mph, and a burned-out clutch.

Sudden, unintended acceleration and fire are the gravest reports. One car sped up on its own and hit a tree, injuring the driver. Two cars caught fire: one while parked at about 1,500 miles and one on a tow truck. Blind spot monitoring misses some vehicles and has been tied to a crash. The infotainment screen often goes black and takes the backup camera with it, and the radio audio cuts out. Other reports describe the engine dying in traffic, a keyless ignition malfunction, a drained battery, and a driver window that drops instead of rising.

Front rotors rust and pads chip or wear out early, often around 15,000 miles. Owners feel vibration and shaking when braking. Dealers treat this as normal wear and charge for the repair. A second pattern involves automatic braking that slams on with nothing ahead. In one case, this caused a skid on a wet road. Owners also describe soft brakes after long drives in traffic, clicking pads, and antilock brake malfunction alerts on a brand-new car.

An airbag malfunction warning flickers on and off during drives, sometimes on cars with under 500 miles. One dealer traced it to a short circuit in the driver's side airbags, which could keep them from deploying or make them deploy early. Both failure modes appear in reports. Airbags fail to deploy in a hard rear-end crash that caused an injury, and airbags fire at low speed after a light curb bump or with no impact at all.

The car surges forward while parking or stopping even though the driver is pressing the brake. This pattern accounts for 4 crashes and 4 injuries, including impacts with a wall and a garage door. Dealers usually find no fault codes. Owners also say adaptive cruise control sometimes accelerates toward slowing traffic instead of braking, leading to a rear-end collision. In snow, buildup on the front emblem blocks the cruise control radar and shuts the system off.

Emergency braking activates when nothing is in the way. Owners report hard stops when pulling away from a green light, during lane changes, in turns when cars in the next lane are mistaken for obstacles, and on empty roads. These sudden stops nearly lead to rear-end collisions. The lane-keeping system also steers toward curves that do not exist, so some owners keep it switched off. One owner was told by the dealer that the braking feature cannot be disabled.

Problems with the forward sensing camera disable several safety systems at once, including emergency braking, traction control, and lane keeping and departure warnings. In one case, a fault code for a wrong mounting position turned up during windshield work, with no warning to the driver. Blind spot monitoring also misses some vehicles, especially on the freeway. Dealers report no codes and say they cannot repair it.