Tutorial: Diagnostics of older Cars without CAN-Diagnostics (VagCom, VCDS-Lite, CarPort) with cheap cable (10400Baud & all control units)
Everyone who tried to do car diagnostics at home with a cheap cable from the web knows the problems: Engine Control units does not open, connection is laggy or shuts down, and so on.
On the web you only read: Only the expensive cables are really working...
Basically these guys are right, but only because they have no clue how to use the cheap cables from amazon, eBay and Co.
In case you want to diagnose your car you are right here.
All we need is the following:
(Norm: ISO 9141-2 KWP 1281 and KWP2000) Price: £8.50/~10€
=> Important is that the cable needs to be controlled with the FTDI Driver.
FTDI Driver 2.08.14 (Maindownloadpage: Link (First Download in list)
Tested Diagnostic Software:
The problem why the cheap cables wont work without this tutorial is the following. The FTDI Driver only allows a baud rate of 9600 in windows.
But most control units (especially the engine control unit) need a baud rate of 10400.
To get the desired value of 10400 baud, we have to do some tricks to the driver.
I read the documentation of the drivers manufacturer and done the needed changes
After installing the driver for your diagnostics cable create a new textfile with the following content:
After that save the file as "obd2baud.reg" and write it to the windows registry with a doubleclick.
If you want you can also download the file here
In order that the changes make an impact you have to set the following:
"System", "Hardware", "Device Manager", "Ports (COM&LPT)" -> Rightclick on "USB Serial Port" -> Properties
-> "Port Settings"
Then change the value of "Bits per second:" to highest value of 921600. (Why you have to do this is explained below)
In order that VagCom starts with the right baud rate from beginning set this value in the options dialog:
If you dont change this setting you will often get the error: "Can't synch baud rate".
The next step should only be done if you encounter further connection problems or shut downs:
Push the button "Advanced".
In the opening window set the same values as on the screenshot below.
Look for the "Com-Portnumber". It can be a value between COM1 and COM4. Other ports are not recognized by VagCom.
Now close this and the previous window with "OK".
Probably you will now wonder and ask yourself why you had to choose this high value of 921600 baud if we want 10400?The solution is:
The reg file replaced the 921600 Baud with the wished value of 10400.
The Configuration replaced the parameters "03,80" with "20,41".
Reversed you get "4120". 4 stands for 0.5 and the number 120Hex is 288 in decimal. Togehter we have 288.5
3.000.000 / 288.5 = 10398.61352
10398.61352 / 10400 * 100 = 99.98666846%
To get now connection errors a tolerance of +-3% is allowed, so that we are within the scope.
Now you can use your VagCom as you want and open all control units.