Hi Steve,
The one further down the exhaust is sensor 4, for the life of me I can't see where sensor 1 is. Don't suppose you have any plans lol where it's located. I've booked it into the garage but have to wait until 17th April 🤦🏻♂️😫. Typical it can't be the simplest one, that's cars for you.
Thanks for your help
Andy