codes shown 45, 51 ,42 whats the probeem starting
code 42 is "intermittent code" (for the ECU presumably)
45 is Oxygen sensor (rich exhaust) 51 (what I could find PROM error [programmable read-only memory]
I'd look at battery and chassis ground as the cause of many on-board computer problems, also check the age of the battery seven years old is TOO old~
Looking for a Used Grand National in your area?
CarGurus has 1 nationwide Grand National listings and the tools to find you a great deal.
Search Buick Grand National Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Buick Grand National Experts