508 blind spot not working

Hello, the blind spot warning system never worked on my second-hand 2020 508 GT-line. The rear bumper was previously damaged and badly repaired. I replaced the bumper and all related sensor cells, but the front and rear parking sensors still work. Interestingly, when the car first starts, the sensors work fine when leaving a parking space. When it reaches a speed of around 40 km/h, the blind spot lights in the mirror turn on, but neither the blind spot warning nor the parking sensors work again. When I turn the car off and restart it for a while, the same cycle begins again. The authorized service center suggested replacing all sensor cells, wiring, and the sensor computer, but they didn't guarantee a solution. I would be very grateful if you could offer some advice on where to focus. Thank you.

I have a similar problem. The blind spot light keeps turning on and off. The service center said let's change it. They said there is a local paint on the front left side, maybe that's why it's happening. I'm waiting now. The blind spot light doesn't work. 2023 508 GT