How to Check Mercedes MB STAR C4 devices using the DOIP protocol using a multimeter.:
VXDIAG Benz multiplexer works the same way.
For those who do not have voltage, we disassemble the C4 or C4 + device, we find the diode as in the photo (circled in red) and look at the value, if it is different, then change it to the one in photo 3, we also measure the voltage on the diode itself. All this applies only to devices where there is DOIP in the configuration.
old style C4 board
New SD C4+ board
solder the diode and everything after this before and after works great
The exchange of diagnostic information over Internet Protocol (DoIP) is performed using a standardized service interface as specified in the ISO14229-2 standard.