Steering Controls / Spiral Cable?

IIRC, the touch tracer on the screen is active ast you touch the buttons and doesn't depend on pressing them. So it must use different wires from the buttons itself. If that's the case, and I'm pretty sure it is, then it could easily be the spiral cable. In fact, that's the most likely cause of those buttons not working.

 

The way Toyota snuck in the Touch Tracer functions without adding more circuits through the spiral cable was kind of clever. You can see it in this wiring diagram screengrab, which shows both the Touch Tracer (*6) and non-Touch Tracer (*7) versions of the wiring.

You can see how, without Touch Tracer, the TRIP and DISP buttons just have their own two separate direct circuits back to the combination meter (DISP to AU1 and TRIP to AU2).

When they add Touch Tracer, they stick a little microcomputer in with the steering wheel switches. They repurpose those same two spiral cable circuits so one of them is now IG (bringing power to the microcomputer), and the other is now TX1, a serial data line that connects to STRG on the combination meter, and sends coded messages about which buttons you are touching and which ones you are pressing.

Those two circuits are separate from the ones for the other media buttons (which are shown in a different part of the wiring diagram).

The big picture is, several separate conductors run through the spiral cable and there is no rule saying they all have to wear out at the same moment. So you can have a situation for a while where some things work and some things don't.

Sometimes you can also demonstrate that whatever isn't working will work if you have the wheel turned a certain way, but not when it's turned some other way. It's a smoking gun for the spiral cable, if you can show that.

 

That's sure more sophisticated than I thought. Thanks for sharing that.

 

Great info!