2018 Hyundai Sonata: What to check before buying

Heavy oil burning with no visible leak is the dominant complaint, sometimes a quart every 750 to 1,000 miles or faster. Low-oil warnings, dry dipsticks, misfires, knocking, blue smoke and fouled spark plugs follow. Some cars go into limp mode, cap speed at 40 mph or seize. Most reports fall between about 65,000 and 118,000 miles. Dealers usually order a 1,000-mile oil consumption test, and many owners report denied warranty claims, though some received a new engine. Four complaints involve fire, including cars that ignited while parked.

Low-oil warning lights and empty dipsticks are the most common report, usually with no leak found. Dealers respond with oil consumption tests and sometimes call the result normal. Reported failure mileages run from about 57,000 to 118,000. Some cars misfire, vibrate, lose power and stall at speeds up to 70 MPH, and one dealer called for an engine replacement. Separate reports describe oil leaking at the drain bolt from a cracked oil pan, which one dealer called a weld crack.

Sudden power loss at highway speed is the main pattern. A flashing check engine light, jerking and a refusal to accelerate come with it. Several cars failed soon after a recall software update at low mileage, and dealers replaced wiring harnesses or sensors. Hybrids show a "Check hybrid system" warning and shut down, sometimes traced to the electric water pump. Other reports describe no-start conditions and failed starters, heavy oil use, and radio static. Three complaints involve fire, and one describes a crash in which neither the brakes nor automatic emergency braking slowed the car.

Cars drop into limp mode with a flashing check engine light, shake, and will not accelerate. Some stall outright at highway speed. Several owners report limp mode shortly after the Campaign 953 software update on cars with only 5,400 to 5,560 miles, and dealers then pointed to engine or wiring harness replacement. Later reports describe knock sensor codes, rod bearing failure, a cracked piston and heavy oil use. One complaint involves fire while driving, one a crash after stalling, and one a back injury from a sudden jerk.

Low-beam headlights light only a short distance ahead, often described as 15 to 20 feet or one to two car lengths. Each beam also casts dark notches or a half-moon shadow that shifts during turns. Drivers report the problem from new and say they rely on high beams on dark roads. Dealers and the manufacturer describe the pattern as an anti-glare design and decline to replace the headlamps. A separate report describes backup bulbs burning out and damaging the bulb holder.

The car accelerates on its own at low speed while parking or reversing, and the brakes reportedly fail to stop it. Five of the 11 complaints involve crashes into poles, walls, trees or posts, several at very low mileage. Dealers often cannot reproduce the problem. Other reports describe limp mode with no response to the pedal, highway stalls with racing RPM, and automatic emergency braking that fails to stop for vehicles ahead. Some owners worry about sudden power reduction after the Campaign 953 update.

These reports describe failures that leave the driver unable to stop. Pedals sink to the floor or go stiff, and four complaints involve crashes, including one fire crash with 11 injuries. ABS faults also appear. A failed ABS module or HECU can disable ABS, traction control, forward collision prevention, auto hold and cruise control at once, and one repair estimate came to about $3800. Other owners report brakes that pulsate and lock up, or automatic emergency braking that engages for no reason and nearly causes rear-end collisions.

Belts fail to retract, lock up and keep tightening during normal driving, or refuse to latch in the buckle. Passenger-side lockups return even after the dealer replaces the unit. Two complaints describe crashes in which the driver's belt reportedly did not hold, with injuries including bruising and a heart contusion. One buckle failure appeared at 45,000 miles, and the dealer confirmed the fault without repairing it.

Airbags failing to deploy in hard impacts is the main concern in this small group of four complaints. One driver ran under a semi truck and another took a hard front-right hit at about 45 miles per hour, and no bags deployed in either case. A police investigator reports a fatal crash in which the steering wheel airbag detached and struck the driver. One owner reports three airbags deploying with no impact while driving at 50 miles per hour.