2020 Prime Ltd w/ 145k mi. Engine and inverter coolant changed about 3 months ago and been fine on other long rides. Riding on highway, orange/yellow Check Engine / MIL comes on... strange. Was driving as normal as always. I pull over and hookup OBD2, torque gives my C0597-chassis. Look it up and seems a rare code without any meaningful, definitive info. Will keep an eye on things but posting here as reference and to keep an eye on. Fluids were all fine. All I can think of was I was probably being cuter than I needed to (should have?) occasionally switching HV/EV mode. Was trying to reserve some EV battery for last couple miles off highway, so I manually switched to HV when first driving on highway and doing uphill stretches / 70+mph (speed limit). But I was switching back to EV for some slight downgrades to use up some EV while not using it all in 5 miles. Probably toggled it 6 times or so. Like I said though, seemed to drive normal. Looking up C0597 I've seen vague and non definitive references to ABS, Cat Convert (I have shield on mine), and other random things. I cleared code and have now driven another 500+ miles (over 2 trips) since without any issue/code... strange!
Any C code is (as you've already mentioned) a Chassis code, so it won't have to do with the cat converter or anything engine-related like that. Moreover, every C0 code has one standard definition from SAE, so when you find multiple, vague, random, online references to different things that aren't even all chassis-related, that just goes to show the internet is full of clueless people. (If it were a C1 or C2 code, it would be manufacturer-defined, and there really would be multiple definitions floating around, different for different cars.) On this list of SAE-standard codes and their fortune cookies, the cookie for C0597 is "Brake System Control Module 'A' Performance". The best place to find more info than that would be the Toyota manual for the car: Toyota Service Information and Where To Find It | PriusChat That will explain exactly what Toyota chose to use the C0597 "Brake System Control Module 'A' Performance" to mean.
I think you can be as cute as you want to be with the hv button, no harm. I use it a lot on any highway trip.
