First a little backstory... When I bought my 2018 Ram CTD 2500 4x4, I paid the dealer for a third key FOB (at a new truck discount). I later had a normal door key cut using the key in the FOB to open the door in an emergency. I tied the new key up under my truck so I could unlock the truck in an emergency. We lost a set of keys a few years ago and were now sharing one key FOB. I could not find it one day, so I decided to use the spare key hidden in the Truck. It had been in the truck, unused for several years. When I used it, the Instrument cluster displayed Wrong Key FOB, but it started the truck. After a few starts, the FOB stopped working, the Instrument cluster stayed dark, but the buttons worked including remote start, but key FOB would not engage the truck once started.
I called a key FOB shop, they explained all the possibilities, they had one new correct FOB, and their technician came to solve the problem. They stated, because the new non-programed FOB illuminated the instrument cluster, this means the old FOB "chip" in the tip became defected. This also means the FOB was the problem and NOT the internal system. They also stated the battery only operates the features of the buttons (door locks, remote start, and Panic). They programed the new FOB in the parking lot with their test equipment. They ordered me a second FOB, and later programed it, with a "two FOB" discount. And, their service was significantly cheaper than the dealership, and their service department could not trouble shoot the truck for a week.
