2015 Kia Optima power train problems

“P1326 code flashing engine light knock sensor went out 3 times in 6 months and just replaced it again and this time engine light didn't go off I was reading that there was a recall on this but apparently mine doesn't state it. Car cannot pass emissions if engine light is on and the 15th of June is approaching. The car doesn't make any sounds or nothing.”

“On December 27, 2025, at approximately 150,556 miles, my 2015 Kia Optima Hybrid experienced sudden engine knocking, power loss, and failure while driving at 65 mph on a highway. The vehicle dropped into limp mode and I had to pull off the highway. The car required towing to the dealership as it would not drive safely. Diagnostics revealed a knock sensor error (P1326 code) and failing connecting rod bearings via Bearing Clearance Test, consistent with the known Theta II engine defect (manufacturing debris causing oil starvation and premature bearing wear). This follows earlier symptoms: Intermittent 'Check Hybrid System' warnings in early December 2025 at 148,665 miles (dealership unable to reproduce, but historical codes noted). The Knock Sensor Detection System (KSDS) software update was performed in February 2022 during prior CHS warnings. Despite onset of issues under the 150,000-mile extended warranty limit per the Kia E2 Settlement, Kia denied coverage due to the minor mileage overage and directed me in a loop between Consumer Assistance and the Settlement Administrator. The defect poses a serious safety risk: potential for sudden engine seizure, stalling…”

“While driving my 2015 Kia Optima (VIN: [XXX] ) at highway speed, the engine suddenly shut off without any warning lights, alerts, noises, or check-engine indicators. This created a dangerous situation for me and surrounding drivers. The vehicle had passed state inspection only 3 months earlier with no issues. The sudden shutdown is consistent with the known Theta II engine defect investigated by NHTSA. The car is now completely undrivable. Two Kia dealerships refused to assist, claiming that they cannot perform KSDS because the engine is already dead. These reasons directly contradict the Kia Theta II engine settlement terms. This sudden stall is a safety hazard and could have caused a severe crash. I am requesting that NHTSA review this incident as a potential recurrence of the engine-stall defect already documented in Hyundai/Kia vehicles.”

“Vehicle experienced sudden loss of power while driving when cylinder 3 completely failed (0 PSI compression). Metal particles found in oil and excessive oil consumption (1 pint/100 miles). KIA dealer diagnosed as piston rings but ignored metal in oil that suggests bearing failure covered under recall campaign. Refused proper diagnostic testing. Vehicle now unsafe to drive with failed cylinder that could cause complete engine seizure while driving. Kia had all recommended services and oil changes since acquired in 11/2016. These service records demonstrate the progression of my vehicle's engine issues, from early oil consumption problems documented by York Auto Care in July 2023 (3 quarts low) to complete cylinder 3 failure with zero compression confirmed by Kia's own diagnostic testing in May 2025. Despite this documented history and Kia's own test results showing catastrophic engine failure, they have denied warranty coverage under their engine campaign that specifically covers bearing-related failures on my 2015 Kia Optima 2.4L.”

“My 2015 Kia Optima Hybrid poses a serious safety risk. While driving at highway speeds, the car has randomly shut off multiple times. A "Check Hybrid System" or hybrid battery warning appears on the dashboard, and the vehicle either loses power entirely or switches to electric-only mode and coasts to a stop. This happens without warning, putting my life and the lives of others at risk. I already had the relevant hybrid system recall work completed by a Kia dealer, but the issue persists and the car remains unreliable and unsafe. This appears to be a known issue affecting many 2011–2016 Optima Hybrid vehicles. Kia needs to be held accountable for continuing hybrid system failures that occur post-recall and outside of warranty. This is a dangerous, recurring defect.”

“Was driving down the highway and all of a sudden the car shut down in the highway lucky cars was not close by. Tried to crank it it would not crank would not take a boost it won’t say anything I had the battery checked at auto zone the battery is really good. The mileage on the Kia optima is 1,900 actual miles it will not crank or move it was very scary I called Kia customer service there wanted to charge me over $400.00 dollars to come get it and take it to the shop so it took me 2 days to find a tow to get it home and it still needs to go to the Kia shop”