VAG-COM Diagnosis: Is Your VW LT Compatible?

Hello,

I own the VAG-COM diagnostic software (version 311.2) and a self-built diagnostic interface. I can successfully read data from various VW and Audi vehicles. However, is it also possible to read data from a VW LT, which is a joint project between VW and Mercedes-Benz? The LT in question is from 2003, so it already has the round diagnostic connector on the driver's side. This connector has 14 pins, with individual pins dedicated to the immobilizer, fuse box, alarm system, airbag, automatic transmission, ABS, and engine control unit. Do these pins correspond to the K-line, and is it possible to access all control units by simply rearranging the connections? Is the L-line, which was required to initiate communication with older control units, no longer needed? I once heard that only the engine control unit of the LT is diagnosable and can be read with VAG-Com.

Thank you very much for your efforts.
Matthias.

Hi,

The engine control unit should definitely work.

Best regards, Rainer.

Hi Rainer,

Does that mean that the pin of the engine control unit is the K-line? If so, then it should also be possible to read the immobilizer (pin 4), the instrument cluster (pin 6), the alarm system (pin 7), the airbag (pin , and the ABS (pin 13) (assuming the K-line is connected). Is the commercially available adapter from 16-pin OBD to round connector only for directly changing the pin assignments (moving the K-line from pin 4 to pin 14 of the round connector), or does the adapter also perform a voltage level adjustment?

Thank you very much for your efforts!

Best regards,
Matthias.

Hi Matthias,

The VW-LT adapter does not contain any electronics; it is a purely mechanical/electrical connection element.

However, one shouldn't try to save money in the wrong places, as problems with reversed positive and negative power supply lines have shown (resulting in sparks...).

Best regards, Rainer.

Hi Rainer,

You're right. This is definitely not the right place to try and save money. However, I still don't understand how the VAG workshops are able to access all the control units (engine, immobilizer, ABS, etc.). The adapter surely doesn't have a switch to change the K-line to the corresponding wires, does it?

P.S. Rainer, the forum is excellent. I haven't found any other forum where the people have so much expertise.

Greetings,
Matthias.

Hello everyone,

I'm bringing up this old topic again because it's the only one that comes even remotely close to my problem.

I have several VW LT vehicles with engine codes AHD and ANJ (which is the main reason I bought VAGCOM).

The error memory of the engine control unit (01) and immobilizer (25) can be read without any problems, but no other control units are found.

Unfortunately, I was unable to establish contact with the airbag and ABS systems.
Since I currently have a vehicle with a burning airbag warning light, it would naturally be very convenient if I could fix it (even though I firmly believe in the coil spring ).

Can someone help me?
Is there a pinout diagram available for the diagnostic connector mentioned above, or could the adapter potentially be modified by soldering?
Or is there perhaps an even simpler solution?

http://shop.dieselschrauber.de/product_info.php/cPath/25/products_id/51

However, don't expect too much from simply manipulating the PIN, in my opinion, the other control units use different diagnostic protocols.

Best regards, Rainer.

Quote:

Do other control units use different diagnostic protocols

How can you find that out? For example, I have the repair manual for the ABS. It describes how to connect the VAG tester 1551 using a specific adapter cable (I don't remember the exact details, I have it all in the office). It also explicitly states that only this tester can and should be used.
Does this have any value, or would it be useful if I published the exact text here?


"From the text in the shop:"

Quote:

By default, access is granted to the engine control unit (01) and the immobilizer (25). Since the round connector to the diagnostic socket is screwed on, the default settings can be easily changed for other control units.

How would I then, for example, assign pin 8 for the airbag/seatbelt pretensioner to test it?
Reflow the connection from pin 14 to pin 8?

I would rather not ruin the control unit.

Hello everyone,
I'm also chiming in on this thread, which I started. Unfortunately, I tried unsuccessfully to access all the control units back then. I bought the adapter from Diagnoseshop and installed a switch. With this, I could switch the K-line to the corresponding control unit pins. However, I could only establish communication with the control units for the engine and immobilizer. Ultimately, I gave up trying to diagnose the other control units.

Best regards,
Matthias.

The LT is a joint project with Mercedes, which means that all other components come from Mercedes and are based on their protocols. The original VAS505x testers have implemented these protocols, while VAG-COM has not.

Your answers don't exactly sound encouraging...

Quote:

The LT is a joint project with Mercedes, which means that all other components come from MB and therefore operate on their protocols.

Besides the engine control unit, and obviously the immobilizer.
Logically, because the engine is from the VAG group.

With the Sprinter (which I also have), I can use VAG-COM via the OBD2 function to read the engine control unit, but nothing else.

Is there any software that is commercially available and allows access to other control units? What about this "Vehicle Explorer" that I've heard of?

Speedy wrote:

With the Sprinter (I also have one), I can read the engine control unit using VAG-COM via the OBD2 function, but that's all. Is there software that is freely available for purchase and allows access to other control units? What about this "Vehicle Explorer" that I've heard of?

Vehicle Explorer is similar to the VAG-COM OBD-2/EOBD function; both essentially do the same thing and only read data from emission-related systems. Specifically, this means that without a Mercedes-specific diagnostic tool, you can only access the engine and immobilizer systems on the LT vehicle.

There have been various considerations regarding LT2 and LT3/Crafter in relation to VAG-COM, but currently, priorities lie elsewhere, so there will be no support for Mercedes-Benz models through VC in the foreseeable future.

That is very unfortunate, but thank you very much for the comprehensive answers .

Hello,

I'm also very interested in this topic, but there's hardly any information available. I found a repair guide for the APA that mentions the VAS 5051/4 cable.

The VW VAS 5051/4 adapter contains a multiplexer, and it is said that the VAS 5051 has a special function called 'LT-Diagnosis.' In this way, VW supposedly has access not only to WFS and MSTG, but also to the rest of the system. I think I have a picture of it somewhere. I'll look for it if there's interest.

I am very interested in learning more about LT (Long Term) diagnosis using VAG-COM.

Best regards,
Sam.

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The multiplexer is essentially a switch that connects between the "lines," allowing the normal VAS-505x to function as usual. The device itself isn't really the problem, but rather the way the diagnosis is performed, i.e., the protocols...

Is it clear that the protocol will be directly implemented in the 5051? Or are they sending the LT devices to MB?
How can I attach an image here? I've dug out the block diagram...