2010 Hyundai Sonata will (usually) only start when being jumped

I have a 2010 Hyundai Sonata with about 100,000 miles. Recently, it started doing funny things when I tried to start it. It would take a few tries, sometimes, or it might start immediately- very unpredictable. Someone suggested I try starting it in neutral, so I did that. It seemed to work for awhile, so the idea was maybe it was a switch in the car that (forgive me because I’m not a car person) can go funny and make it so the car won’t start in park. Switch replaced, so everything’s fine, right? No, still not starting on the first try. I took it to a car parts store to get the battery tested. The guy said, the battery is shot and is definitely the problem (he also said the starter was okay and he thinks alternator is also okay). So I bought a brand new battery and had it put in… STILL NOT STARTING! Sometimes it will start in neutral, sometimes in park. It does not seem dependent on the temperature, the amount of time it’s been since it was last started, or anything else that I can figure. However, if it is hooked up to a jump start, it will start immediately with no problem, in park. New switch, new battery. Is it likely the alternator? I’m trying to figure out how big of a hit this might be to my checking account. Other than this problem, the car runs perfectly. I’m confused that people keep diagnosing a problem and it still doesn’t work. And that I might have replaced parts that weren’t broken to begin with.

@lindzsc16
" Recently, it started doing funny things when I tried to start it. It would take a few tries, sometimes, or it might start immediately- very unpredictable."

What Happens When It Won’t Start Right Away?
Does The Engine Crank Over Like It’s Trying To Start Or Just Click Or Do Nothing?

CSA

@lindzsc16
A Hyundai Technical Service Bulletin #13-EE-001 (Updated Jan/2013 To Include More Model-Years) Discusses Starting Problems With Some 2010-2013 Sonata And Santa Fe Models.

It covers models with the 2.4L engine. Is that what you have?

Apparently on vehicles that won’t start, but the starter motor spins without cranking the engine, some are found to have a broken starter motor lever.

The well written bulletin, 11 pages with color photos and diagrams, outlines a bench test diagnosis and disassembly of the starter and replacement of the lever if needed.
CSA

@lindzsc16
A Hyundai Technical Service Bulletin #10-EE-001 (Mar/2010) Discusses Starting Problems With 2009 & 2010 Sonata Models With The 2.4L Engine During Extended Below Freezing Conditions.

Again, an excellent 5 page detailed bulletin with nice drawings and guidance.

Cars with this problem just click with no cranking during starting attempts.
The starters will operate normally after several attempts to crank.

If this describes your situation and it’s been below 32F for periods when you have this problem then the starter may need a Starter Solenoid kit 36120-2G110.

See a dealer for availability and application.
CSA

It sounds like it is trying to start sometimes. Other times, it just clicks. I asked a different car place to look at the receipt that was printed out when they checked the battery and he said something is drawing a LOT of power…

So sometimes it cranks – that rrr rr r rr sound – but doesn’t catch and run. And other times it just clicks, no rrrr rrrr rrr sound, just a click, eh? … hmm … that’s a tough one. Usually it is either one or the other.

So what’s wrong? hmm… well, my first guess the starter solenoid contacts are a little fried. They’re not making a good low resistance contact and it causes a reduction in electrical power available to run the starter. Starters us a lot of power, 1000 watts and higher. Without enough power, it could just click, or it might turn, but too slow to start the engine.

If the starter weren’t engaging the engine you’d still hear that rrr rrr rrr sound but it would sound like it was spinning much faster than normal. I presume you aren’t hearing anything like that.

There’s no need to guess though. A mechanic should be able to easily do a voltage drop test to determine if the solenoid contacts are fried or not. Or if you fill lucky and want to avoid more testing, just replace the starter motor and cross your fingers, the solenoid contacts are part of the starter motor on most cars these days, so you’d get them replaced plus the lever problem noted above.

Until then, if this problem only occurs on the first start of the day, in the morning, you could probably put a battery charger on the battery over night to keep it topped off. You’d want the kind that trickle charges the battery. That might provide enough ummph to get the car started in the AM, then the heat of the engine and the alternator charging may be enough to start the car the rest of the day.

I asked a different car place to look at the receipt that was printed out when they checked the battery and he said something is drawing a LOT of power...

I’m guessing that something is the starter itself. Replace the starter.

I'm confused that people keep diagnosing a problem and it still doesn't work. And that I might have replaced parts that weren't broken to begin with.

Welcome to the world. I’m afraid this is the norm nowadays.