Brake light switch pinout? failed Hall effect sensor?

Our 2012 Prius C brake lights started to flicker and then stayed on, sometimes flickering, about a week ago. This was odd because the car was off and nobody was within 100ft of it and unfortunately we were on vacation more than 1000km from home. I got the switch out and, being far from home, hoped I could lubricate or examine switch contacts but it's a Hall effect sensor! So it ought to last forever and nobody stocks it and it's expensive but seems to have failed regardless. Does anyone know the pinout to test if this sensor is actually pooched?

I've gotten home and have ordered a new part but it'll take some weeks to arrive and I worry that the sensor may not be at fault. Alternate causes are guessed to be: poor wiring on previous owner's alarm system install (partly removed on the road, the rest pending now that I'm home with real tools); or rodent damage to wiring looms in engine compartment or deeper under dash.

I'd love to be able to test my brake light sensor conclusively so I can know how much time to invest in pursuing my alternate causes.

Any assistance or links to other threads about this brake light "switch" would be most welcome. I couldn't find anything.

Pic of the "switch" opened up shows rare earth magnet on sprung plastic slider in white plastic + PCB with FET topside I think. A couple small ICs on the backside of the PCB but I can't even see the Hall sensor in my pics really.

 

Yes I'll try to get access to the relevant parts of the RM for the pinout. I've also ordered a decent BT OBDII tool to get more complete code output than my cheap old junker provides.

Thanks mr_guy_mann and Electroingenieur for the leads. I'll try to write up what I learn for reference.

 

I wanted to post a follow up in case anyone else ever lands on this thread.

1. the situation got worse before it got better, but at least it led somewhere.
The brake lights issue was the only noticeable symptom for some time and few other codes were thrown but the replacement part I ordered was not the correct item so I couldn't swap and confirm it was actually the sensor. As such I kinda sat on it for a week or two. Then one day I hopped in the car to drive my daughter-who-missed-the-bus-not-entirely-her-fault to school and things were much worse. Doom and gloom notices on the dash display told me to pull over immediately but most critical systems were still working fine. A quick test around the property before taking to public roads indicated that I had full brake and boost but no ABS, no cruise, no steering motor assist and no speedo as the main display was intent on having me end my "research". Hilariously the brake lights were now working fine but clearly things were much worse. I drove back roads to get my daughter to school, went home and directly to friend's garage where we started looking at codes, which were much more plentiful now and ultimately I left it with him to puzzle through. He texted me later that day to say that now the car wouldn't start and he was still digging.

2.Central CANbus brain freeze can be lethal.
The issue was ultimately traced to a communications module that seems like something of a CAN bus master or network connection module. There's a pic of the module in question and it's piggybacked on the bracket that holds the hard-to-find 3rd fuse block beneath the dash near the hood release and OBDII connector. The sticker reads "computer multiplex network body" and the communications of many systems seems to depend on this unit being up and running. A used unit was ordered for a fraction of the price of new and we waited with fingers crossed. It arrived a couple days ago and it solved any and all problems JUST LIKE THAT! Apparently the hall sensor brake light switch was fine so I'm glad it opened it carefully without damaging it during my initial investigation.

3. Don't let amateurs put extra wiring in your car.
The most likely culprit for frying the multiplexer unit, at least to my mind, is shoddy aftermarket wiring undertaken on behalf of a prior owner who had a remote starter installed (in a Prius, yes) as well as a transponder for one of the local toll bridges. I started removing all this sloppy non-stock wiring when the problem with the brake lights first showed up and my buddy Simon finished digging the last bits out of the steering column while he waited for the new CAN brain to arrive. I can't prove that a short circuit from poor insulation or incorrect connections to various stock systems is at fault here but the birdsnest of wires and relatively sloppy install makes me suspect alarm and starter guy a lot more than Toyota engineers.

4. I think that the hall sensor switch for the brake pedal is actually two halls sensors, one for lights, and the other for cruise control cancellation. It certainly looks like the PCB has a pair of identical little ICs that could be hall effect sensors and that they're set side by side (purple circle) such that the small magnet on the slider (green circle) will sweep past them both simultaneously. I think I got this idea from a wiring diagram but now can't remember. The larger transistor on the rear of the sensor board PCB (see photo earlier in thread) may very well be switching current to the brake light LEDs but the way the CAN brain failure caused brake lights to come on and sometimes flicker without actuation at the sensor suggests that the lights are not actually being switched here in the sensor. Anyway, just posting these details in case they help someone else some day.

Thanks to all who offered assistance and leads.