2021 Hyundai Sonata: What to check before buying

On hybrids, the 12-volt lithium battery goes dead soon after the car is parked. Drivers have to reset it again and again, and dealers often find nothing wrong. Other reports describe the car shutting off at highway speed and then restarting normally. A burning smell under the dash, melted fuse receptacles and cracked wiring harnesses knock out the AC blower, and some cars wait months for backordered parts. Turn signals, door lock buttons and rear window switches work only some of the time. Several complaints call the burnt wiring and battery problems a fire risk.

Sudden loss of power at highway speed is the main pattern. The RPM spikes, an oil pressure or overheating warning appears, and the car drops into limp mode until it is restarted. On the 2.5L turbo, the thermostat housing is the suspected cause. Misfires and stalling lead to fuel injector replacement, sometimes all four. More serious cases include an engine replaced at about 14k miles, an engine that seized with no oil three days after an oil change, oil burning, knocking, and a blown head gasket on a hybrid. Backordered parts keep cars at the dealer for long stretches.

The dual-clutch transmission loses power. The engine revs but the car will not gain speed or goes into fail-safe mode, often with no warning light, and a restart clears it. Reports cluster between 35,000 and 44,000 miles. Many owners connect it to recall 22V746000 but find their VIN is not covered. Others say the software update did not help or caused harsh shifting. Shifter malfunction warnings, replaced transmissions and a $13,000 repair quote also appear. Smaller groups report losing coolant with no visible leak and fuel tank recall faults.

These reports are a mix of problems. Some drivers smell strong fuel in the cabin, and dealers cannot reproduce it. Others describe the car surging or jerking while idling with the brake held, or speeding up and slowing down on its own. One owner was asked to pay $1,600 for a fuel assembly tied to a recall that has no remedy yet. Hybrid owners report the battery dying every couple of weeks. In one case, warning lights came on, the shifter locked, and a transmission shift actuator repair took 3 weeks.

Most filings involve fuel recall 25V796000, and dealers have no parts for the repair. One car was out of service for more than 89 days. Symptoms include stalling without warning, popping sounds, high fuel use, and a strong fuel smell inside the car that dealers often cannot reproduce. Separately, the car shakes and will not accelerate, with a check engine light, and the fix is replacing all four fuel injectors, in one case at 47,000 miles.

In crashes, the air bags fail to deploy. There are two crash reports with seven injuries, including a front collision where automatic braking also did not engage and a deer strike at 45 mph. One owner says the front crash sensors are mounted too low to trigger unless the headlights are destroyed. Separately, the passenger occupant sensor switches off the front passenger air bag for a short adult sitting on a cushion.

The panoramic sunroof shatters without warning. Some drivers hear it explode on an open highway with no debris around. One says it happened in the driveway about a minute after turning on the defrosters on a frosty morning, and the dealer blamed a rock chip. On the N Line, which has no auto wipers, the wipers turn on by themselves, often when the turn signal is used. One owner says a recall still has no remedy.

The panoramic sunroof shatters while driving, usually at highway speed. Drivers describe a loud bang like a gunshot, with no traffic ahead and nothing that could have thrown up rocks or debris. In some cases the glass breaks outward, and none of the drivers saw cracks beforehand. Every filing in this category describes this same failure.

Braking failures go both ways. In one crash report, the brake pedal feels locked and will not go down, automatic emergency braking does not step in, and a front collision warning appears after the impact. The other report describes automatic braking that is not needed. The ABS grabs while backing out of a garage, and the emergency braking system applies at 60 mph for no reason before letting go a few seconds later.