Hi there does anybody know what the replacement bulb number is for a 09 Sierra Denali reverse light says 921 online but recon and manual say 4057.

 

Only 2 screws to take the tail lamp off just pull it off and check the bulb. Easiest way to know for sure.

 

Sylvania bulb guide says reverse is 921 and the signal/brake are 4157NA

Edit to add
Its still a good idea to check, I work in the shop for a living and I'd say at least 2/5 listings are wrong for everything ooooorrrr the parts guy at the last 3 shops is special with a capital "R"

 

07-08 most were 3047 (AKA 4157)
09-10 most were 921 (AKA the large peanut bulb)
11+ they switched back to the 3047

Should be able to i.d. yours without pulling the taillamp. The two bulbs are very different in size.