2018 Kia Optima Plug-in Hybrid problems

“My 2018 Kia Optima has the Theta II 2.4L engine. In February 2026, the dealer performed an engine/powertrain computer reprogramming. In August 2026, the engine failed and the vehicle was taken to an authorized Kia dealer, where the engine was replaced under the Theta II engine warranty. The vehicle was at the dealer from August 8 until the repair was completed on September 29, 2026. When I picked up the vehicle on October 9, it felt shaky and vibrated on the drive home. On October 11, the vehicle began giving off a distinct, unfamiliar smell that is not like burning fuel or oil. On October 21, I found the vehicle leaking an opaque, milky tan fluid onto my garage floor. The type and source of the fluid are UNKNOWN. I have photos of the leak. My family and I have stopped driving the vehicle because we believe it is unsafe. We were driving it with our children before these symptoms appeared. Given the history of Theta II engine failures, we are concerned about the risk of engine failure, stalling, or fire while driving. The new symptoms have not yet been diagnosed or confirmed by a dealer. I am arranging for the vehicle to be towed to a Kia dealer for warranty…”

“I am submitting this complaint regarding ongoing and persistent mechanical issues with my vehicle since the time of purchase. The vehicle has repeatedly shut off unexpectedly, creating a serious safety concern. Initially, I suspected the issue might be related to the battery, and I have replaced the battery twice within the past 4 years. However, the problem has continued. In January, the vehicle began shaking and shutting down again. I took it to a mechanic, who diagnosed the issue as faulty spark plugs and an ignition coil. The diagnostic codes provided were P0303 and P0456, and the recommended repairs were completed. Approximately one month later, the vehicle began shutting off again. I then took it to the dealership, where I was advised that the valve cover gasket needed to be replaced, along with the belts, and that a fuel system cleaning was required. I subsequently had these repairs completed by my mechanic. Less than a week after completing those repairs, the vehicle once again began shutting down. A diagnostic scan then produced code P123300. In addition to these repeated shutdowns, the vehicle consumes an excessive amount of oil, has poor…”

“There is already the theta 2 campaign on my Kia optima but Kia is not upholding their warranty for a new engine. Kia customer care told me that untill my car actually throws a rod then they will not fix it. So I could be doing 80 down the freeway and jeopardize not only my safety but everyone else's for them to uphold their lifetime warranty? Also upon doing further investigation and I don't know how many cars this pertains to but the fuse box in my 2018 actually belongs to a 2016 which if you look it up yes they are comparable but don't offer all the same functions or power that my 2018 needs to run I fully believe Kia knew this when they were being built on the factory line because it just so happens that there is about 6 different versions to the pcb relay that can fit from a 2016 to a 2020 k5 but for some odd reason every car got something different why?”

“Purchased vehicle from a used car dealership. Had it a few months before brake pedal started losing pressure and going to floor. Had master cylinder replaced. A few months later, brake light started coming on when accelerating. New master cylinder had leaked into brake booster. Had master cylinder replaced along with brake booster. A few weeks later and brake pedal is losing pressure again”

“The contact owns a 2018 Kia Optima. The contact stated that while driving at an undisclosed speed, there was an abnormal odor and a knocking sound coming from the engine. The vehicle was taken to the dealer; however, the dealer was unable to duplicate the issue. The vehicle was not repaired. The issue persisted. The contact stated that the vehicle was later returned to the dealer to be repaired under a service campaign involving the engine control unit (ECU). Shortly after the vehicle was repaired, the ECU failure message was displayed. The vehicle subsequently became inoperable. The vehicle was not repaired. The manufacturer was notified of the issue. The approximate failure mileage was 1,500.”

“On August 26, 2025, I brought my 2018 Kia Optima Plug-In Hybrid to an authorized dealer for recall SC218 (engine inspection and KSDS software update). The dealer verbally stated both SC218 and SC278 recalls were completed, and the repair order (RO #XXX) lists them as performed. In September 2025, Kia America emailed me showing recall SC218 still open, and a warranty coverage report dated September 26, 2025, again listed SC218 as unclosed. On November 4, 2025, NHTSA’s official VIN lookup confirmed the recall remains “Incomplete.” On October 21, 2025, Kia America emailed me under Case #XXX stating that SC218 was “confirmed completed” and that the dealer performed a software update to the ECU, referencing RO #XXX. However, NHTSA’s database still lists recall SC218 as incomplete. This contradiction between Kia America’s internal record, the dealer’s invoice, and the federal NHTSA database raises a serious safety concern that the recall inspection or software update was never actually performed or was never reported correctly. I have requested written proof and diagnostic data (Battery SOH report) multiple times but have not received them. If accurate, this means I…”