Scenic preheating lamp stays on

Greetings! This sounds similar to an issue I encountered with my old Opel Astra. The diesel engine had preheating problems too. The glow plug light stayed on, and the car ran rough. Did you check the relay and fuses related to the preheating system? Perhaps there is a blown fuse or a faulty relay causing the problem, like a short circuit in your home.

Thanks for the tip! Which relay and fuses do you mean exactly? Where did you find them, and how did you find out it was them?

With my Opel, the relay and fuses for the preheating were in the engine compartment's fuse box. I consulted the car's manual to locate them. Considering your Renault Scenic's symptoms and your suspicion of a defective preheating control unit, a visit to the workshop seems advisable. They can precisely diagnose the electrical gremlins in your ignition system to fix the part that needs fixing.

Cheers, I took it to the workshop as you suggested. Turned out to be a defective cable to the preheating unit as I thought. Cost me 95€ to repair. All good now!