I have a GF4A-EL on my 98 Mazda 626 GF 2L and strongly suspect the TSS is defective. I can't find any sensors for my tranny, but I have read that the FN4A-EL is just an improved version of the GF4A-EL and was wondering if their turbine speed sensors are compatible, since there are allot of the former easily available.
The sensor visually look identical and are top mounted in the same way.
EDIT July 3, 2016
I just ran across this diagnostic sheet for the TSS on the Mazda 3 which also uses the FN4A-EL transmission and it looks the same as for the GF4A-EL.
Input/turbine speed sensor resistance
250—600 ohms (ATF temperature: –40—160 °C {–40—320 °F})
I've found the part numbers. The one for the GF4A-EL is FW01-21-550 and it looks like this:
The one for the FN4A-EL is FN01-21-550 and it looks like this:
Based on the testing procedures, it looks like the two sensors are electrically identical, and they also look like they are physically identical except for that metal tab which is used for screwing them down.
I'll bet that that metal tab can just be pulled off and rotated 90 degrees to turn a FN01-21-550 in a FW01-21-550.
Considering I can get the former for $14 shipped free from Hong Kong and the later I can only get from the dealership for about $100, I think I'll take the chance, and update this edit into an answer if it works.