VAGCOM Adapters: Mass Measurement Data

Hello VAGCOM users,

For the design of an adapter without an optocoupler, measurement data regarding the adapter's internal ground connection between the PC and the car would be helpful.

Could the owners of ready-made adapters please check with an ohmmeter what the resistance is between pin 5 of the PC-COM connector and pin 4 of the OBD socket?
to measure?

Of particular interest are adapters that, according to the manufacturer, do not have optocouplers built in.
According to my estimate, relatively low values, probably below 100 ohms(?), should be measurable there.

Additional information about the provider and the model designation may also be helpful.

Sure, here's the translation:

"Thank you in advance."

Hi Ulf,

I have, as is well known, an adapter from Auto-Intern that, according to its description, does not use an optocoupler.

Between the specified pins, I measure 1.1 ohms. When the measurement probes are shorted together, my digital multimeter shows 0.2 ohms, which effectively means 0.9 ohms.

Regarding the pin assignments: According to the description, pin 4 is "vehicle ground," while pin 5 is "signal ground." I'm getting an infinite reading on pin 5, which indicates a disconnection. I believe they're referring to the socket in the car, so the connector is a mirror image. Therefore, if you've counted the pins differently, and pins 4 and 5 are swapped, you would get an infinite reading as the result.

Best regards,

Jan.

Jan6K wrote:

I measure 1.1 Ohms between the specified pins. When the measurement probes are shorted together, my digital multimeter shows 0.2 Ohms, so the effective resistance is 0.9 Ohms.

Hi Jan,

Thank you for the measurement; it seems like a good starting point for a product developed by professionals.

Quote:

Just to clarify the pins... according to the description, pin 4 is "vehicle ground," while pin 5 is "signal ground." I'm getting an infinite reading on pin 5, so there's a separation. I think they're referring to the socket in the car, so the connector is a mirror image (pin 4 is the fourth pin from the right in the top row, the right one of the two longer pins). If you've counted the pins differently, and 4 and 5 are swapped, then you would get an infinite reading as the result.

I think you've already measured correctly.
"Infinity" would, in turn, suggest a galvanically isolated adapter, which yours is not .
"If you're going to do something, do it right." In that case, there should be no connection to either the vehicle ground or the signal ground, which would mean your design is "inconsistent."

In my car (and also in the adapter cable for the Pocket diagnostic tool), only pin 4 is connected, while pin 5 is free.
So it seems that, in case of doubt, the OBD information refers to the vehicle's weight, which corresponds to pin 4, and your measurement is quite plausible in that regard.