Will the bolts loosen up a bit if the system is warmed up thus making it easier to remove? Tried it cold & cannot shift either bolt for love nor money!!!

 

If you are unable to undo the bolts for the back box you may find it easier to undo the 2 bolts where the centre section meets the downpipe, these are spring loaded and tend to be less tight. Then pull the whole exhuast out from under the car and undo the bolts between the back box and centre pipe then.

Dousing the bolts in WD40 an hour or so prior to undoing them also helps.

 

I ended up using an air impact wrench on mine after soaking them with penetrating oil. I wouldn't recommend warming up the system as it's too easy to burn yourself. It may make it easier if you have a gas torch so at least the surrounding area isn't hot. This all assumes some muppet hasn't replaced the bolts with normal mild steel ones. If they have then it could be time to get the hacksaw out!

 

Managed to sort it with 2 sockets, one on the nut & one on the bolt after having warmed it up which did seem to help. Result. Got a nice shiny tailpipe now