Adding cruise switch to basic version

It almost looks like the ECU can't see a Cruise Control there at all. Possibly it's something which is flashed into the EPROM when the car is built? Sorry, I have no idea if its something which can be reprogrammed, or it might actually need a different ECU?

Maybe @Elektroingenieur might have some idea?

[PS - I've sent a note to the Moderator - maybe they can change the Prius c?]

 

My posting from September 2017 has some background information. I still don’t know if it’s possible, as it was on older models, to add conventional (constant speed) cruise control to a fourth-generation Prius car just by installing and connecting the switch.

I’m not aware of any settings (“Customize Parameters,” in Toyota’s terms) for this. As @alanclarkeau kindly notes, there may be differences in the ECU software, but in general, Toyota’s published information doesn’t discuss how to add features that weren’t on the vehicle when it was built and aren’t offered as dealer-installed options. Since the safe, reliable operation of the hybrid system depends on complete compatibility among the hybrid vehicle control ECU, engine control module, skid control (brake) ECU, and other ECUs, I’d recommend against any software configuration not approved by Toyota.

I wonder, though, if your car might simply be missing some part of the wiring for the cruise control switch circuit, described in the U.S. and European editions of the Repair Manual and Electrical Wiring Diagram (more info). At the hybrid vehicle control ECU, on connector F3—uppermost of its three large connectors—is there a beige wire on terminal 14? Without this, the switch won’t do anything.



If the wire is there, if you carefully¹ disconnect the connector and measure² the resistance between terminal 14 and body ground, does it change as you operate the cruise control switch? The resistance should be normally open (≥ 1 MΩ), 1510 to 1570 Ω with CANCEL pressed, 618 to 642 Ω with – SET ▼ pressed, 236 to 244 Ω with + RES ▲ pressed, and < 2.5 Ω with ON-OFF pressed.

¹ The connector is not sold separately, only as part of the complete wire harness.
² Be careful when probing connectors. The terminals are tiny and can be damaged easily; as you may know, it’s best to probe from the wire side with very thin test pins, such as those sold by Toyota.

 

It’s true, as I wrote, that Toyota doesn’t offer constant-speed cruise control on Prius cars built for sale in Japan, but the required logic for it might be present in the hybrid vehicle control ECU anyway. Have you looked for the wire at terminal F3-14, as I described above?