Hard engine starting?

2015 HYUNDAI SONATA
90,000 MILES • 1.8L • AUTOMATIC
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JOHN BELL6
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my 2015 sonota 2.4l limited is having intermittant long starting issues, does not seem to be affected by the amount of time it sits with the engine off. sometime first start of the day is normal sometimes long. i was have problems with the car just dying on me but it would start right back up, replaced fuel pump 6 mos ago no problem since. no codes, i was thinking fuel pressure leak down. battery is good starter is good doesnt turn over slowly. just seems to take about 4-5 seconds to start.
Sep 20, 2026 at 10:59 AM

What to check next

Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.

Start with the returning U0109-00 code. Have a technician confirm its Hyundai-specific description and status, identify the reporting module, and check communication with the fuel-pump controller. Inspect its applicable power, ground and wiring using the correct diagram before buying another pump. During an actual extended-cranking event, compare commanded and actual fuel pressures with the specifications for the confirmed engine. Check the low-pressure supply before condemning the high-pressure pump. Neither the code nor a ticking sound alone proves that the high-pressure pump has failed. Do not loosen direct-injection fuel lines to check for fuel. Repair the demonstrated electrical or pressure fault, then repeat starting checks under the conditions that caused the problem. The returning code gives the shop a focused lead and may help avoid replacing unrelated parts.

Guidance references and applicability

HELLA: Checking a high-pressure fuel pump https://www.hella.com/techworld/en/technical/sensors-and-actuators/checking-a-high-pressure-fuel-pump/ General reference for diagnostic data and checking low-pressure supply before high-pressure diagnosis. Its example pressures are not Hyundai specifications. HELLA: Fuel-pump control modules https://www.hella.com/microsite-electronics/en/Fuel-pump-control-modules-157.html General controller background, not a Hyundai U0109 diagnostic procedure. Confirm the exact code definition and circuit against vehicle-specific service information.

Read the replies · Discussion summary and reported outcome

AI-ASSISTED GUIDANCE · REVIEWED BY 2CARPROS
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MECHTRIX
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Yes it Could be a fuel related problem like a pressure regulatorleak down failing pump or relay and such ..or eavan somthing simple like a dirty maf sensor thats easy never hurts to clean that first.... but honestly it sounds more like this might be a failing crank or cam sensor just strange that you havent got a code for it yet somtimes you dont see a code right away when the problem is just beginning but you said its been going on a while right ? Strange that theres no code yet .yeah id say clean the maf sensor first its easy usually takes 5 or 10 mins then see if it runs better drive it around a little and let us know what you find ..hope this helps good luck
Sep 20, 2026 at 2:26 PM
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MECHTRIX
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Oh" and while youre cleaning the maf sensor you could clean the throttle body too that would help alot . Best of luck hope this helps
Sep 20, 2026 at 2:30 PM
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JOHN BELL6
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Ok, so 6 months ago I had to replace the in tank fuel pump due to a U0109-00 code. Now it's back, high pressure fuel pump?
Sep 22, 2026 at 7:18 PM
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JOHN BELL6
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Oh, checked maf, crank sensor and cam sensor.
Sep 22, 2026 at 7:20 PM
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STRAILER
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If I can jump in here, did you service the throttle body? Also, we need to run the codes, and yes it can be the high pressure fuel pump. Is the engine making a ticking noise at idle? If so this can be the HPFP. Here is a guide and video to help us see what is going on.

https://2carpros.com/articles/engine-cranks-excessively-before-starting/

and

https://www.youtube.com/watch?v=LBCpCWEFnTg

Let me know and if you can upload a video of the engine idling it would help.
Sep 24, 2026 at 7:32 AM
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MECHTRIX
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  • 549 POSTS
Yes when you mentioned having a high pressure fuel pump that threw up a red flag for me so yeah probably should check that too that would be a good thing
Sep 24, 2026 at 1:48 PM
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MECHTRIX
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  • 549 POSTS
If youre saying that's what you have e is a high pressure pump m8ght be part or all of the problem ...but also it a giid idea to clean the throttle body as I meantiined earlier..
Sep 24, 2026 at 1:51 PM
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Discussion summary

Hard engine starting?

The owner described intermittent four-to-five-second cranking on a 2015 Sonata identified in the question as a 2.4L Limited. An earlier in-tank fuel-pump replacement reportedly resolved stalling, but the owner later reported that U0109-00 had returned. Contributors discussed fuel-pressure loss, sensors, throttle-body cleaning and the high-pressure pump. No measurements or successful repair were reported.

Reported outcome: The earlier stalling reportedly stopped after an in-tank pump replacement. The later extended-cranking concern and returning code remained unresolved.

The question identifies a 2.4L engine while the vehicle fields list 1.8L. The engine configuration, code status and reported sensor checks need confirmation. No fuel-pressure readings or controller-circuit results were supplied.

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AI-ASSISTED SUMMARY · REVIEWED BY 2CARPROS
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