2020 Hyundai Sonata: What to check before buying

The HVAC blower quits, often on and off, leaving no heat, A/C, or defrost. Reports point to a poor connection in the wiring harness under the fuse box, with melted blower fuse connectors and repeat dealer visits. One owner waited months for a back-ordered harness. Front passenger window regulators fail with a loud crunching noise, reported at 31,000 and 82,931 miles. Other reports describe no-starts even after a new battery, a fogging right headlight, a slow fuel gauge, and stalls at intersections, one of them tied to a crash.

The fuel tank swells under pressure until it bends the floor under the rear seat, lifts the seat cushion, and can push the exhaust down. Drivers hear a loud boom or popping, see the fuel gauge drop fast, smell gas, or watch fuel spray from the filler area. Some get a check engine or powertrain warning first. Others get none. Dealers cite a vent valve and a service campaign, yet many cars sit for weeks awaiting direction, and one repair quote reached about $6,000.

These reports center on the fuel system recall, NHTSA campaign 25V796000, and some owners say the recall part is not yet available. The failures match the swelling-tank pattern: a booming sound, strong gas odor in the cabin, fast fuel loss, fuel backing out during refueling, and a deformed floor under the rear seat. Mechanics point to the canister purge valve. In one case the rear seats grew hot enough to melt. Repeat failures after repair also appear.

Sudden deceleration on the highway is the most serious pattern. The car drops to about 10 mph while check engine, ESC, and traction control lights flash, and several dealer visits have not fixed it. Stalling and rough idle show up early, some under 2,000 miles. Others describe hard shifts and shaking at idle, a P0768 shift solenoid code with power loss, and acceleration that stops near 4,000 RPM. Several reports here actually describe the swelling fuel tank.

Coolant disappears and the engine overheats, often with thick white smoke or steam from the exhaust and an empty reservoir. Several of these reports involve Sonata Hybrids, and repeat failures after repair are common. Dealers have replaced the EGR cooler, and one car sat waiting on a back-ordered thermal management module. Other reports describe highway stalls with every warning light lit, a fuel rail sensor failure that recurred at 6,000 miles, and fuel tank expansion with a popping noise.

Much of this category is the swelling fuel tank again. It damages the metal floor under the rear seat, sometimes with no warning, and owners cite Service Campaign 9B1. Separate patterns stand out. Rear doors fill with water when it rains and drain when opened, and dealers struggle to find the source. Factory paint peels on the hood, bumpers, doors, and quarter panels. A poorly seated driver window causes wind noise. Single reports mention frame rust and doors opening while driving.

Most of these reports describe the fuel tank expanding under the rear seat. Drivers hear a pop or boom, the rear seat rises and can turn hot, a gas smell appears, and the tank may refuse fuel or spew it at the pump. Some cars wait weeks for a recall remedy. A separate problem affects the driver's seat itself, with cracked frame bolts at 34,458 miles and a failed weld that leaves the cushion tilted. One heated seat burned through.

A rubbing, raspy, or whining noise develops in the column when the wheel turns, reported under 15,000 miles. Some cars also develop excessive play in the wheel. A dealer diagnosed a worm shaft assembly that needed replacement. Other reports describe erratic electric power steering with a blocked-radar warning at 975 miles, and the car swerving on its own at highway speed. One crash with an injury followed two rear tire failures at 65 mph.

The passenger airbag turns off when a short passenger sits on a cushion or wears a long winter coat. Owners say dealers and Hyundai corporate will not change this and point to seat belt protection instead. One body shop refused to raise the seat. Several filings describe this same concern in similar language. A separate report follows a 50 mph crash into a parked car, after which the insurer questioned whether the airbags or sensors worked.