My cousin has a 2010 Jaguar XJ supercharged issue with the transmission. He says the light comes on followed by the car cutting off, having to shutoff and restart the car. I don't speak mechanic but i felt like I knew enough to tell them that they may need to have the transmission cleaned so did I say this right?

 

You didn't provide enough detailed information to give you any meaningful advice, except that your cousin should immediately take his XJ to a Jaguar dealer or qualified independent Jaguar mechanic for diagnosis and repair. The light coming on means that something happened to cause one of the computers to issue an On Board Diagnosis (OBD) fault code, which a mechanic can read to properly diagnose what happened.

Trying to fix it by trial and error and not knowing exactly what is wrong can be a very costly mistake. And it's unsafe, because you stated that the car cuts off when the light comes on. That can result in your causing an accident if it happens while you're driving in traffic.