My Onan 5.5 was giving me a Code 58 and shutting down about 5 min after start-up. That sensor shuts the unit down at 1200 degs I replaced the Exhaust Gas Temp but heat issue continued. I must add that this unit only has 73 hrs and my Wife had complained about excessive floor heat since the unit was new! We have an Axxess 30 ft.... it was quite a job getting to the Onan to remove the cover. I removed the muffler assembly, cut the muffler open and found a clogged Cat.....so I removed the cat converter and welded the muffler back together.......my exhaust temp went down to 214 degs at the area where the cat was and 178 degs on the exit end of the muffler. No more heat issues !!