Toyota Yaris 2006 Car Radio

Pull the two side bands, starting from the bottom edge.
Remove the four screws.
Unlock the three interlocking snap in at the top: push the tabs with your finger while you pull the frame.
Pull the radio block, releasing the four mounting pin-push (pink color).
Release the three connectors and the antenna plug.

Steering wheel commands

There are five buttons at the steering wheel: volume +, volume -, channel up, channel down and mode. At the radio side there are only three wires connected to the 20 pin connector.

Here it is the schematic:

With a multimeter we read the resistance values at the radio receiver connector while pressing each button:

Resistance at SWG - SW1
No buttons pressed	100 kΩ
Seek +	0 Ω
Seek -	329 Ω
Vol +	1000 Ω
Vol -	3110 Ω

Resistance at SWG - SW2
No buttons pressed	100 kΩ
Mode	0 Ω

so we calculated the resistor values:

Steering Wheel Commands Resistors
R1	100 kΩ
R2	100 kΩ
R3	330 Ω
R4	680 Ω
R5	2200 Ω