P0841 on mazda 5, cleared the code didn't come back
 

Hey my Mom just purchased a 2007 Mazda 5 from a dealership. Drove fine, purchased it, on the way home the check engine light came on. P0841 was the code. Cleared it and it didn't come back. The transmission oil is clean and red but, smells like burn't drywall. We took it back to the dealer they checked the codes and didn't find the code again, and wouldn't do anything about it, not even a flush. Should she return it? It as 119,000km on it. What could have set the code off? thanks