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2018 Kia Optima - Limped to dealer and stayed 3 months

My car went into limp mode as well. I brought it to the KIA dealership and they had my car for over 3 months. The Dealership said that they need to change the motor, but they never did in the first place, they only change the wiring harness to the knock sensor. I drove it for 15 minutes and it started to sputter again. So I took it back to the dealership to see whats wrong with it and KIA couldn’t pinpoint the problem. My 2018 KIA Optima was losing power going uphill making noises. So I continue to drive the car for a few months and the noise keep bothering me so I called KIA corporate and brought it to another KIA dealership. They said that the First KIA dealership installed the wiring harness wrong ( chasing the wires) my wires were fraying …which its dangerous. So they installed it the second time, I drove it for two hours and the problem came back, took it back fail the piston test and they replace the engine assembly and the car is running good.

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Sorry to hear about your experience but I’m glad you finally got the car fixed. Happy motoring.

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It’s runnning now? Trade it!!!

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So my questions are…
What was wrong with the engine?
How is/was the motor oil level on the old engine?

An inoperative knock sensor could damage an engine; all depending upon a few things but it should be noticeable to the vehicle driver by chronic pinging which may come across as a subtle rattling upon acceleration or uphills.

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The Hyundai/Kia Theta II engine strikes again!
They have a tendency of failing rod bearings.
H/K claims it’s caused by debris left in the engine from manufacture.
A whistleblower says it’s a design issue.
Goes back to 2013.
There is a class action lawsuit.

There is a safety recall requiring H/K to add software to use the knock sensor
to also detect rod knock, and go into “limp mode” before it gets so bad the engine stalls on the road (which is quite unsafe.)
They do this to all cars with the Theta II when they come in for maintenance etc.

Unfortunately the original wiring harness can cause false positives.
Instead of just replacing the harness when they add the software patch
they use their customers as guinea pigs to see if their original harness is problematic.

Sometimes, like in the case of the O/P, the engine already had a rod bearing starting to fail when the software & harness was installed.