Temperature Control Unit - Celcius Conversions

Maybe this is an option you can change with techstream? Seems simple enough

 

That's the beauty of firmware. Identical hardware, completely different programming. We know that the MFD is hard-programmed with the geographic data like language and temperature for that region. My guess would be that something like the radio is also hard programmed.

You could most likely read the firmware out with the proper programmer, modify the hex, reprogram the MCU, and voila it will be celcius. Probably one bit in the entire hex. The problem is finding the bit.

The good news is you have both boards. If you can identify the MCU, you can maybe find the pinout and type of programmer. Then maybe read the hex out, compare the two, and see what the differences are.

 

One of our members figured out how to reprogram the TPMS module for 5 tires so he could have the spare tire included. We cannot tell much from that complicated circuit board except to say it is a well-made marvel of miniature surface mounted components. and the bigger chip(s) probably hold a lot of computer code.

 

That's not really reprogramming. Toyota TPMS should be able to register 7 sensors. It's just using techstream.

Looking at the supplied image you can clearly see a crystal leading into the microcontroller. It's firmware driven.

Pins are also extremely expensive, especially in an automotive environment. For AECQ type qualifications you have to design and prove that any pin to any surrounding pin shorted isn't a problem. Also all the ways things can die. For automotive, each pin is a giant PITA. If you can put it in firmware, it is much easier to certify the code. Still a pain, but much easier since there aren't environmental problems...

 

It was reprogramming I think...he sent code to the TPMS system...Techstream does not allow fiddling with TPMS config, at least without special commands we would not be aware of, for Gen2 anyways

 

From the logo silkscreened on the board and molded into the plastic chassis, I think the A/C control assembly in your photos—which are pretty good, by the way—was made for Toyota by Tokai Rika Co., Ltd., or one of its affiliates. I doubt they’ve published any information about it, however.

Considering the number of units that would have been made and the lack of other ICs on the board, the 100-pin QFP IC in the center is probably an application-specific integrated circuit (ASIC), a custom chip produced specifically for the A/C control assembly on the Prius and perhaps other vehicles, with an integrated microcontroller, memory, LIN bus interface, LCD and LED drivers, and switch inputs.

The connector pinout is in the Repair Manual, available by subscription to techinfo.toyota.com:

2 (TX+) LIN communication signal
3 (SWO) Steering pad switch assembly signal
5 (IG+) Power
6 (ILL+) Illumination power
7 (ILL-) Illumination ground
8 (GND) Ground​

The Repair Manual also has a System Diagram page, with a block diagram showing how a different part, the A/C amplifier, is connected to the sensors, actuators, and other ECUs on the car, and a summary of the LIN communication from the A/C amplifier to the A/C control assembly:

Ambient temperature indicator signal
MODE indication signal
Blower level indication signal
Set temperature indication signal​

and from the A/C control assembly to the A/C amplifier:

AUTO switch signal
A/C switch signal
Fr DEF switch signal
Rr DEF switch signal
MODE switch signal
REC/FRS switch signal
Micro dust and pollen filter mode switch signal
Blower switch signal (FAN+, FAN-, OFF)
Set temperature switch signal (UP, DOWN)​

It’s clear that the A/C amplifier is the brains of the operation, doing the actual control functions; despite its name, the A/C control assembly just has the switches and indicators.

Toyota’s Electronic Parts Catalog gives the same part number for the A/C control assembly (55900-47120) on U.S., Canadian, and LHD European models, which show the temperature in different units. Toyota’s practice seems to be to assign different part numbers for different firmware, since dealers aren’t expected to do reprogramming when replacing parts, so I expect the LIN temperature indication signals from the A/C amplifier to the A/C control assembly tell it whether the readout should be in Celsius or Fahrenheit.

That may not be the end of the story, however: the A/C amplifier part numbers also seem to be common between the U.S., Canada, Europe, and Japan:

U.S.
88650-47310 ZVW30..G,S MOON ROOF-WITH(SOLAR PANEL)
88650-47330 ZVW30

Canada
88650-47310 ZVW30..G,S MOON ROOF-WITH(SOLAR PANEL)
88650-47330 ZVW30

Europe
88650-47300 ZVW30..ARL,EUR MOON ROOF-WITH(SOLAR PANEL)
88650-47310 ZVW30..LHD COLD AREA SPEC&MOON ROOF-WITH(SOLAR PANEL)
88650-47320 ZVW30..ARL,EUR
88650-47330 ZVW30..LHD COLD AREA SPEC

Japan
88650-47300 ZVW30..G..CBU ムーンルーフ-有り(ソーラパネル)
88650-47310 ZVW30..G..CBU 寒冷地仕様(有り(リヤフォグランプ))&ムーンルーフ-有 り(ソーラパネル)
88650-47320 ZVW30..CBU
88650-47330 ZVW30..CBU 寒冷地仕様(有り(リヤフォグランプ))​

It’s not described in the Repair Manual, but if I had to guess, the A/C amplifier selects the temperature units based on information it receives from another ECU on the car, like the combination meter or the multiplex network body ECU, that would have different firmware in different regions. That’s how I would design it, anyway, to minimize the number of different parts.