ISC Learning?

Never heard of such a thing. I've had Prius batteries disconnected dozens of times. Connect it back up and drive it. You might have to re-enter some of your settings like radio presets and back-up beeper if that's been altered from factory. But it'll drive fine. It might not be as efficient as it might be, but it'll learn as it goes.

 

Highlander Hybrid is an example that needs ISC, but Prius does not.

 

May not apply to the Prius, but I found this ten year old TSB for Lexus:

 

Yes, the HiHy ISC process is similar. As a practical matter I don’t bother with that process because the hybrid ECU will eventually do the learning in the course of normal driving.

 

In the Repair Manual (more info) for the 2015 Prius, under General: Introduction: Repair Instruction: Initialization, Toyota writes:

“When the auxiliary battery is replaced or the cable is disconnected from its negative (-) battery terminal, the ISC learning value will be initialized and symptoms as a loud rattle from the hybrid vehicle transaxle assembly may occur until ISC learning is performed. Therefore, perform ISC learning when the auxiliary battery is replaced or the cable is disconnected from the negative (-) terminal of the auxiliary battery.”​

That paragraph has a link to the ISC learning procedure, under Engine/Hybrid System: Hybrid/Battery Control: Hybrid Control System: Loud Rattle From Hybrid Vehicle Transmission, which is similar to the ISC Learning Procedure on page 2 of the EG021-07 bulletin kindly posted by @RRxing. Unlike the bulletin, which says to drive the vehicle to warm up the engine, the Repair Manual says to enter inspection mode (i.e., maintenance mode, to keep the engine idling) first, presumably for the same purpose.

 

So I had the dealer tell me my low MPG after I did my sparkplugs and a few other things myself was beacuse the computer didnt learn the ISC values. Unfortunately I redid the brakes and had to disconnect the battery again.

I followed the ISC learning procedure, but I don't have tech stream. Will this still work? I'm still getting low fuel economy around 41 MPG.