What would happen if you didn't use Type IV?

[pmccumber]

I have a 2003 with the 5 spd. It takes the Type IV fluid.

I had the transmission fluid swapped (not flushed) at the local Toyota dealer. What would happen if they used the previous gen of fluid instead of the Type IV?

That is, does it damage it? Reduced performance?

 

[OGBeno]

Nothing.