I haven't found any real consistency in which discount code gives the best rates for any given rental. As a result, I manually enter many of the codes I have until I find a good rate. I repeat this process with several rental car companies.

Even limiting codes to those to which I am legitimately entitled, that's still a lot of codes. Since I don't check them all, I always suspect that one of the unchecked ones would have been the winner.

How does everyone else check the impact of different codes on pricing?

I'd love it if I could enter all the codes to which I am entitled once, and a tool would check pricing for each one. Does anyone know of something like this?