Application Note AN1055
How to find out the steering wheel control signal is resistive or digital
CarPC JoyCon Exc/Exd/Exr
Before you choose JoyCon and install JoyCon at your vehicle, you need to find out the steering wheel control signal is resistive or digital.
1. The digital signal may be LIN or CAN or vendor defined signal.
2. The resistive signal is measured as voltage.
1. Where to get the steering wheel control signal
There is two point where to get the steering wheel control signal
1. from radio connector
2. from clockspring
The two signal may be same or different.
For example,
In the case of Hyundai or Kia, the clockspring signal and the radio connector signal is same, resistive.
In the case of BMW E90 E91, the clockspring signal is resistive but the radio connector signal is CAN.
2. How to find out the steering wheel control signal is resistive or digital
If you can not find the wiring diagram or repair manual of your vehicle, you need to find out what kind of signal is your steering wheel control signal. You need to check the signal at the two point, the clockspring and the radio jack.
A. Check the steering wheel signal wire voltage of the radio jack with the test meter without disconnecting the car radio.
If the voltage is sustained and the voltage of each button is different while the steering wheel button is being pressed, the steering wheel control signal is resistive. 
Or if the voltage of each button is same, the signal is digital. 
B. Check the steering wheel signal wire voltage of the clockspring with the testmeter without disconnetting the car radio. And check if the signal is resistive or digital in the same way above. 
If the result of A and B is same, the steering wheel control signal is delivered directly to the car radio. If the signal is resistive, you can use CarPC JoyCon Exr/Exd/Exc. 
If the result of A and B is different, the steering wheel control signal is processed by a control module and delivered to the car radio as digital signal. Most of the digital signal of radio Jack is CAN BUS. You can scan and use the CAN messages with CarPC JoyCon Exc. 
