Kadjar brake booster error

Sounds like the brake booster pressure sensor is faulty. Has the brake system been bled recently? Incorrect bleeding can cause this.

Yes, I bled the brakes last month. What does incorrect bleeding have to do with the sensor?

If air gets trapped during bleeding, it can mess with the pressure readings and damage the sensor over time. It's a common issue. You should take it to a workshop.

Thanks for the tip. It was the brake booster pressure sensor, likely damaged during bleeding. Replaced it for 90€ and all's good now.