2012 Hyundai Sonata: misfire or rough idle

Filed Jul 8, 2025 · Brakes, Electrical · IL

I drive a 2012 Hyundai Sonata Limited. After a recent fill-up, I began experiencing delayed acceleration, engine hesitation, and what appears to be misfiring—especially at low throttle. Most notably, the brake lights stay illuminated even when the car is turned off, which drains the battery and poses a major safety hazard. I scanned the vehicle with an OBD-II scanner and received code P0504, which points to a brake light switch malfunction. I also noticed that pressing the start button with my foot off the brake still starts the engine instead of going into accessory mode—confirming abnormal brake signal behavior. I replaced the brake light switch, which temporarily fixed the issue, but the symptoms returned within a day. After researching, I found there was a recall (the federal safety agency 15V759000) for a nearly identical issue involving the brake light switch and stopper pad. However, my VIN is not listed, even though I am experiencing the same safety-critical symptoms. This issue poses a significant safety risk on the road, and I believe my vehicle should be included in the affected population of the recall or issued a Technical Service Bulletin extension.

Filed Mar 31, 2024 · Engine, Fuel system · NV

Approx one year post engine replacement, and 2 weeks prior turbo system replacement, I am having major issues with my sonatait struggles to stay started, it always hesitates and doesn't want to move when I press accelerator, shakes jolts and shudders, the smell of burning oil comes thru the vents and even smoke comes out from under the vehicle. The engine is leaking masses amounts of oil that seem to be leaking from all over the under carriage and half way to the back underneath the car, oil is in the wheel wells, and even splashed on the rims, the spark plugs are covered in oil, huge plums of white and dark smoke come out of the tailpipes, literally blinding anyone behind me, press the accelerator to the floor and it just shudders and smokes even more, check engine light is on and states malfunctioning turbo system, boost pressure sensor malfunction, sluggish will not gain speed, oil within the turbo blow by hose and in intake hose area, now I have coolant pouring out and the reservoir the coolant will be literally boiling. This is not good at all especially after a year post engine replacement and turbo replacement. When the car is started I push start and car struggles to start the starter keeps screeching and car shudders for a good 45 seconds before it either dies out or finally starts. This vehicle should be a lemon and bought back regardless of age condition etc. A vehicle after engine replacement of only one year should not be pouring oil out of the engine, failed head gaskets,misfiring and leaking coolant. I keep receiving recall notice after recall notice in the mail stating I have recalls that need to be addressed but when checking using my vin it says there are no recalls needing fixing, that makes me uneasy and I don't feel safe driving the vehicle I lost faith in it all together

Filed Feb 12, 2021 · Engine · 120 miles · NY

On thur feb 11th on my way to work my vehicle lost power and stalled. I called oit of work because it was not working properly. The code for misfire in cilinder 4 came.up. Taken to a mechanic he changed the spark plugs and coil, said there is no compression coming from the 4th cylinder tells me this has been comon for the 2.0 told me ill need a new engine. The vehicle was in motion when it suddenly putted and started to lose power. I have never had an issue due routine maintenance.

Filed Dec 6, 2020 · Engine · 141,062 miles · LA

My car stalls all of the sudden out the blue during driving sometimes it kills causing me to almost get hit a couple times because it just goes out during driving. It has a misfire and a strong scent of exhaust coming from the car. I have take it to mike morgan hyuandi in louisiana where the mechanic clearly tells me they feel the misfire and smell the exhaust but no engine lights are on so no codes can be read and they cant do anything. He even told me if I'm driving and the car stalls try to get a video of the rpms of what the car is doing and reading during that time so he can have something to go off of, boy how unsafe was that advice. I have taken this car to gateway as well as a local mechanic all who has put it on the diagnostic machine yet still noone can find the issue because again it has no check engine lights on so what do I do. I dont have money to just buy parts and hope that fixes it. The car drinks oil but there is no visible oil leaks. No droppings in my drive way. Some one told me the pcv valve may needs to be changed but again I dont have money to keep changing out parts hoping thats it. This is a known issue with these cars and I feel hyuandi needs to do something because it's nothing that all consumers are doing wrong the motors are just no good

Filed Dec 11, 2018 · Acceleration, Engine · 93,000 miles · GA

Had motor replaced from a previous recall, 4days after this fix I noticed a rough idle. Went to numerous shops incld dealership was told by dealership that recall was done and any other repairs would be out of pocket. Problem has progressed from rough idle and engine noise to poor acceleration and mistimed boosts. As in when entering highway car doesnt accelerate very fast very long delay before boost intiates. Once at desired speed when slowing down car boosts without pressure to accelertator!!! Now that winter has arrived, sporadically on cold start car idles even rougher and sounds as if it with shut off. When driving in traffic car idles rough then shuts off!! No power steering! No lights ! No power! This happened whilst car is in drive and in motion! I try to avoid hwys and night time driving when I can as im scared to death of this car. I purchased it used in dec2017 11 days later intial issues began with car loosing power. Now after issue was "fixed" by replacement motor same intermediate lost of power issues again but with the added boosting issue as well now.