Hyundai Solaris, 2024 model. Used to get 50-55 km on 5 liters, now it's down to 40 km. No weird noises, seems to drive fine, but it's guzzling gas like crazy. What could be the reason - spark plugs, injectors, oxygen sensor?
First thing, check your tire pressure - even a slight underinflation greatly increases rolling resistance and fuel consumption.
After that, it makes sense to scan for diagnostic errors even if the warning light isn't on, because the oxygen sensor, spark plugs, or injectors usually cause glitches that show up in the ECU's memory.
On such a new car under warranty, I'd head straight to the dealer - there's no point guessing, and they'll quickly pinpoint the cause with their computer.
The last time I went fishing and was out on the lake, I noticed that with improperly inflated tires, the boat motor burns through fuel noticeably faster - so definitely start with checking the pressure, it's obvious but it actually works.
Plus these days in 2024 the electronics are more complex, and an oxygen sensor issue or a problem with the fuel mixture can show no signs on the outside until the transmission starts running in compensation mode - that's when all your fuel economy goes out the window.
I'd also add: a clogged air filter is pretty common and takes just a couple minutes to check, and then the system runs a rich mixture. You should get a diagnostic done anyway, because no error codes doesn't mean all your systems are working optimally.
On a 2024 Solaris, a 20% jump in fuel consumption is serious, and it's usually caused by the most basic things. They already suggested checking tire pressure, and that really does work, but besides that you should pay attention to the engine air filter. If it's clogged, the car runs rich and burns through fuel noticeably faster, and the filter itself only takes five minutes to clean.
Next is diagnostics by scanning for error codes, even if the check engine light isn't on. On a car this new there's an oxygen sensor and fuel injection control system that can work in error mode, and the computer starts running in emergency mode with over-enrichment. This doesn't always trigger the light. Honestly for a fresh car this is the quickest way to find the answer - ten minutes of diagnostics will reveal everything.
Spark plugs and injectors usually cause a fuel consumption spike much later, after the car's already done 100,000+ kilometers. On a new Solaris the sensors and electronics act up first, not the mechanical stuff. Check the side door pockets and the front part under the hood - something could've gotten stuck there, like a rag or whatever, that's catching on the air intake and causing a vacuum leak.
I had a case where a friend complained about the same thing - his fuel consumption jumped from normal to just insane. Turned out it was a dirty air filter that clogged the intake and messed up the air supply to the mixture. The oxygen sensors were getting wrong signals as a result, and the system was over-enriching the fuel. After cleaning the filter, everything went back to normal.
Plus to the recommendations above - really start with the simple stuff: tire pressure, filter condition, maybe even the oil's too old and thick. At this stage you usually don't need diagnostics. If that doesn't help, then scan for error codes - injectors and the O2 sensor could be the culprit, but most of the time they're secondary factors after you figure out that the basic mechanical condition is fine.
Spark plugs and injectors on a 2024 Solaris usually aren't to blame for such a spike in consumption - it's a relatively fresh car. I've been driving for a long time and I remember when consumption suddenly jumped on my car, I thought that was it - turned out the air filter was clogged, there wasn't enough air, and the engine was running rich. After replacing the filter, everything went back to normal.
But before you replace the filter - check the tire pressure, that's the most common culprit. Then it makes sense to scan for error codes with a diagnostic tool, even if the warning light isn't on. On newer cars, the electronics often miscalculate something, and that immediately eats up fuel.
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