Transmission oil (to change or not)

Since you aren't sure of the last fluid change, would advice you have it replaced.

Transmission fluids, or anyotger fluids, degrades with time and usage. Yo be on a safer side, change it.

Ensure you use the right transmission fluid(WS Toyota brand).

 

how many km's do you hope to keep it for? it is a simple procedure, if you can find a mechanic who will follow instructions.
if your 'oil changers' are anything like ours, i would not let them touch it.

 

Here in the US, Toyota has no scheduled changes recommended, so we tend to make up our own.

I advise 50,000 km, then 150,000 km then every 150,000 km.
(in your case you have missed 50,000, so 100,000 km, then 200,000 km then every 150,000 km)

Prius C Tranmission/Transaxle/HSD Oil Change | Page 6 | PriusChat
has pics.

 

Sorry I don't have Aqua (aka Prius c in the North America?) transaxle fluid change instruction, but you can be fairly certain it is:

1. Raise and level the car
2. Remove transaxle fill, then drain bolts (just for insurance remove fill bolt first, in case you encounter difficulty)
3. Reinstall drain bolt, preferably with new, proscribed washer (Torque value for both is 29 ft/lb, so perhaps the same)
4. Run a hose and funnel down to fill hole from above, pour Toyota ATF WS fluid, till it overflows
5.. Wait for overflow to subside, install fill bolt, again preferably with new washer.

According to Prius c Owner's Manual, proscribed fluid spec and quantity:

 

Addendum to above (edit is locked out):

29 ft/lb torque is regular 3rd gen Prius, possibly the same.

 

Is the washer for the transmission drain bolt the same as the engine oil drain bolt's?

 

No. Again, this is 3rd gen, not sure how much it applies to Prius c (it might well be identical), but anyway: the tranxaxle drain/fill bolt (identical) washers are bigger, p/n 90430-18008.

And the bolt is cap screw (round headed bolt), with a 10 mm hex recess. You can get socket wrench drivers, Stanley for one.

Honda by comparison, is also cap screw, with 3/8" square recess, so any 3/8" socket wrench extension works fine.

 

I'm just impressed by how kind of you... Thank you so much for the explanation.