How to Choose a Fully Pinned 38-PIN Cable for MB SD C4?

Here we share user working experience on older Mercedes with HHT-WIN software.


Here goes the story.

“I got the C3 and C4 from Aliexpress, both HHT-WIN has problems accessing EZL and DM modules.  I received my third multiplexer-MB SD C4 DoIP from obdii365.


3rd C4 & my 2015 Star diagnostic Software – Engine OFF
LH and GM communications works
EZL and DM communications does not work

3rd C4 & borrowed known-good 2018 Star diagnostic Software from nearby MB independent repair shop – Engine OFF
LH and GM communications works
EZL and DM communications does not work

3rd C4 & my 2015 Star diagnostic Software – Engine OFF
LH and GM communications works
EZL and DM communications does not work


Then I figure out the problem. This C4 multiplexer works.

I was super frustrated so I borrowed a known-good cable from JSP Porsche MB Independent Service.
When I used the good borrowed cable with the C4, all the car scanning functions work properly — even while the engine is running!
When I used the Apliexpress 38-pin cable, the EZ and DM scanning functions do not work.
Well I am relieved — now I just need to get a good functioning cable!!!

So in sum:

My first MUX – the C3, worked to scan the GM and the LH, but not the EZL and not the DM. I suspected it was the cable, but I just returned the whole thing.
My second MUX – the AliExpress C4, worked to scan GM, LH, EZL, and DM ….. but only when the engine was off / ignition was on. I suspect the cable was fine, but some weird voltage thing was going on inside the MUX that made it intolerant of the higher voltages with a running alternator that precluded it from scanning EZL/DM with the engine running.
My third MUX – the obdii365 C4, actually looks to be a quality unit (it is a bit more polished than the Ali C4) but the cable was defective…… which caused it to not be able to scan the EZL or the DM — ever. A full 22 of the 38 pins were not hooked up!!!!!

I was suggested to get older software than they sell (they sell as far back as 2018 software) because the earlier software works better with HHT-Win (I think.)


EZL Live Data While Engine Running Money Shot Below:

MB SD C4 EZL Live Data 1 MB SD C4 EZL Live Data 2 MB SD C4 EZL Live Data 3 MB SD C4 EZL Live Data 4 MB SD C4 EZL Live Data 5

38-pin diagnostic connector pinout diagram that specifically talks about 124/129/140/170/202/208/210 models.

Mercedes Benz 38 Pin Diagnostic Connector

Aliexpress was not able to send me a fully pinned out cable. Their “manufacturer” doesn’t make a fully-pinned cable.

I took $40 and spent it on who claimed, when I contacted them, that their cable is fully pinned.

It is not that easy to find a 38-pin cable where all the pins are connected to the C4 connector.

I asked a bunch of ebay vendors about pinouts for their 38-pin cables. Many of them did not get back to me.

However, the vendor for these advertisements on ebay confirmed that NOT all 38 pins are hooked up, although it does look like pins 7 and 17 (EZL) are definitely hooked up.
It also looks like pins 18/19 are tied together, and I am not sure if the DM would work, let alone other special 129, 210, and 140 special functions past pin 20 which are NOT hooked up.

Mercedes Benz 38 Pin Diagnostic Connector 2

I tried the obdii365 38 pin cable with my C4. Guess what?

IT WORKED PERFECTLY. EZL and DM readings worked fine. I received the cable today and it works! DM, EZL, LH, GM … all accessible!

Mb Sd C4 Doip Review W124 1 Mb Sd C4 Doip Review W124 2 Mb Sd C4 Doip Review W124 3 Mb Sd C4 Doip Review W124 4 Mb Sd C4 Doip Review W124 5 Mb Sd C4 Doip Review W124 6

Then we switched back to my cable. Nope-a-roo! No EZL and no DM readings!

Also guess what? It appears his cable and my cable are visually different!!!!

Benz 38 Pin Cable Comparison

Up: aliexpress 38-pin cable with only 16 pins attached

Down: fully pinned cable from obdii365


Tip: Do not buy the 38 pin cable from sellers on AliExpress either.
Their cable also does not have the required number of pins hooked up.

Cable Comparison 2



A couple of things about the C4 MUXES along the way if anyone choses to buy one. There seems to be a couple flavors of these that all look very similar.

  • Try to get a newest designed c4. My first AE c4 mux was cheaper and had no wifi, and I think it was an older design. When I got it and connected it to the car, it would constantly flash messages about needing to insert rechargeable batteries to address some charging issue, and it didn’t sound so good even though conventional wisdom on benzworld and mhhauto was to just ignore the message. Also, my first AE mux had rust stains on the heat sink under the rubber protectors, misspelled labels, screws on the end panel (where the connectors are) that didn’t screw in, and uneven places on the heatsink that were shiny/dull/shiny/dull. I did not take out the circuit board to look at it, but all these things made me nervous so I sent it back. The newer c4 I got had none of these issues.


  • The newer c4 muxes all typically have wifi. At first I thought wifi is just another thing to go wrong, but I quickly realized that it is quite useful. The mux uses wifi to connect to the SDS laptop on its own SSID. You can decide to not use wifi and then you connect the mux to your laptop with a long ass ethernet cable with funky rj45 connector, but what I realized is that it is really easy for the green cable get tangled up in the radiator fan!


  • There are two wifi “models” of c4 muxes…regular wifi and I THINK (not certain)DOiP. The regular one is kind of a pain to set up. You have to first connect the mux to your laptop with the green cable, then set a static IP on the laptop for the wifi adapter, then go into a funky software program that sets up the mux, then manually set two SSIDS for the mux to broadcast … “Road24” and ”Workshop” ….. and then set static IPs for the mux to use when using those two SSIDs, the unplug then green cable and the hope the laptop connects to the mux and never touch that shit again. The newer ones, MB SD C4 PLUS DOIP, are much easier. Just connect the laptop to the wifi SSID the mux is broadcasting out of the box “XC4PLUS” and you are done. The mux itself has a DHCP server inside and leases an IP address to the laptop.


  • If you are using this mainly for your w124 then 2015 Star diagnostic software and WinXP is good. It works well as long as it has HHT-WIN. You can just run DAS which brings up HHT-WIN or execute HHT-WIN directly. In my troubleshooting, I borrowed an SDS laptop from JSP MB that had 2018 software on it. It had HHT-WIN in it too with Win 7 but was significantly clunkier. I had to run XENTRY, which then brought up DAS, which then decided to (emulate?) HHT-WIN in a goofy vertically stretched window. It worked, but it felt like there was more to go wrong.