HEX CAN Interface Test -> kein CAN? | Posts 16+

Hmm, so if I disconnect the two CAN lines from the control unit or speedometer, or whatever..., nothing will work anymore...


Please note: This is for Leon models with ASV (Adaptive Suspension System)!
For vehicles with an automatic transmission or an electric vehicle (EV), this is different for the motor.


The speed signal and other data are all transmitted via CAN bus, not directly through a 12V signal or tachometer shaft.

I also recently installed an ECU from a Passat 3BG into a Leon 16V...it works the same way...

What engine and features does it have, and more importantly, what is the model year?
Starting in late 2003, there was a change.
As I said, I'm referring to my ASV motor. As mentioned above, that is exactly what I wrote.
Since Ulf is also experiencing the same issue with his car's CAN bus and he also has a 'basic' Polo, it will likely be the same problem.

However, I'm confident about the comfort features, as I was looking for a CAN-based alarm system for my Leon. It seems that no other car has this feature.

Best regards, Jochen.

In terms of comfort features, it's the same starting from 2001; everything uses the 1C0 959 799 interface, which is CAN-based. However, the original instrument cluster isn't connected because it doesn't have an MFA (Multifunction Display) that can interpret this data.

Here's an example: If you disconnect the KomfortCan, then the signals from the door control units are correctly connected.

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Okay, as I said... I've already installed CAN-based tachometers in vehicles up to the MJ99 series of the 1M without any problems... It works fine because the ABS and airbag control units send data via CAN!

legolas09 wrote:

The ABS and airbag control unit send data via CAN.

That will likely be the case with my Polo as well, if you look at the SLP data.

The only thing that seems to be missing is the software-side "activation" of the physical pair of wires present in the OBD connector, allowing them to connect to the internal data flow within the CAN bus.

ulf wrote:

The only thing that seems to be missing is the software-side "activation" of the physical pair of wires present in the OBD connector, allowing them to connect to the internal data flow within the CAN bus.

This happens through the gateway, if you know how - no, I don't know how either.

I'm happy to hear that the AI is working for you.
The question remains: are you sure it's really CAN that you got from?
On which pins (green connector) did you take the measurements?

My AI unit also claims to be CAN-capable according to the version (***920***), but the CAN bus is definitely not active, even when the AI is running. I believe that communication is only happening via the K-line.
And this would also be true in cases where a diagnosis hasn't been made. In that scenario, the AI would still provide all the data even without access to the CAN (Controller Area Network) bus.

If the ABS and the engine control unit communicate via CAN, then the terminating resistor at the instrument cluster should be measurable. Please try measuring this with the vehicle turned off. You should measure 60 ohms between CAN-high and CAN-low. If nothing is measurable, there is no CAN communication here either. I now suspect that communication may also be happening via the K-line in this case.

I have received confirmation from various sources and verified through my own measurements that the MEIN Msg does not have any CAN hardware.

As I mentioned before, CANalyser detects nothing, there are no idle levels, and the termination resistance cannot be measured -> therefore, the CAN bus is not functional!

Best regards, Jochen.

Okay, so the comfort CAN is now connected to pins 8/9 on the green connector...

and
19 - Data Bus (CAN), high-level input signal.
20 - Data Bus (CAN), low-level input signal.

If I get a score of 19 out of 20, the speedometer is just busy displaying error messages in the error memory.

Errors, corporate data bus, etc.

So, the comfort CAN is now connected to pins 8/9 on the green connector...

and
19 - Data Bus (CAN), high-level input signal.
20 - Data Bus (CAN), low-level input signal.

If I get a score of 19 out of 20, the speedometer is just busy displaying error messages in the error memory.

Errors, corporate data bus, etc.

That's it.
Pin 8/9 is not connected on my device, which means I don't have the comfort CAN functionality.

And the engine CAN bus doesn't exist in an ASV (Autonomous Shuttle Vehicle). If you have a PD (Parking Device), or an automated system, or ESP (Electronic Stability Program), it works differently. In those cases, there is a different control module (MSG) from a hardware perspective, as I mentioned before.

Please post your engine version so we know which engine you have and why the Engine CAN is active in your case.
If you browse the Leon forum, you'll find the same information that I'm providing here and what my measurements have shown.
It's interesting to find out what happens when the comfort CAN bus is not connected. If there are no errors then, which I understand is likely to be the case, it simply means that there are unused cables present.

@Ulf
Both the wiring diagrams and the cable harness documentation were helpful in this case. You'll need to directly measure the voltage to see if the CAN bus is actually active.
Your 'simple' Polo will end up being like my Seat.


Best regards, Jochen.

Okay, so I have an ARL engine... The motor-CAN system exists in all TDIs, as well as in the BAM, AUQ engines, and in the 1.6 8V/16V and 1.8 20V engines.

'As I mentioned before, the comfort CAN bus in the Leon is not connected to the instrument cluster. These cables were omitted because the LEON's speedometer cannot process these signals due to the lack of a large MFA (Multifunction Display). With my VW speedometer, things are different. When it's installed, it lacks the comfort signals and cannot perform functions like the light buzzer or door monitoring. The error memory indicates that the comfort CAN bus is missing. Now, if I connect the two 10cm cables from the comfort control unit to the instrument cluster, everything works as you can see in the pictures... so data is likely being exchanged there.'

Feel free to try disconnecting pins 19 and 20 and attempting to start the car... good luck. The first error you'll likely encounter is related to the airbag system, and the second will probably be something related to the ABS/ESP systems, etc.

So, I have an ARL... the engine CAN is present in all TDIs.

This is definitely wrong!
The ASV does NOT have a CAN bus. For the PD engines, it would be necessary to measure this, as I believe there should be one present, since it is needed for ESP and other functions. The VP 37 diesel engine can operate without a CAN bus and does so.
According to Volkswagen, the smaller gasoline engines (1.4 and 1.6) also do not have a CAN bus system. Regarding the larger engines, I believe it's the same as with the PD engines.



As I mentioned before, the comfort CAN bus in the Leon is not connected to the instrument cluster.


Then we are already in agreement .


You can try disconnecting pin 19/20 and attempting to start the vehicle... good luck... The first error you'll likely encounter is related to the airbag system, and the second will be something like the ABS/ESP, etc.

No, there's no mistake; you can always check with me if you need to.
I have a parallel tap connected inside, hoping to be able to read CAN data. However, the entire CAN bus is completely dead, as mentioned above.


Best regards, Jochen.

Okay, it seems we're not making any progress here... and since you mentioned seat-leon.de, feel free to email 'RED-DOG'. He has a 1.6 engine and might be interested in my KI (presumably referring to a specific part or product).

Regarding the 'Comfort-CAN'... why is it proof that there's no such thing as a 'Comfort-CAN' just because the speedometer isn't connected?

There are 4 types of CAN buses, and up to 3 of them can be installed in the Leon, depending on the equipment.

MotorCAN, ComfortCAN, InfotainmentCAN, and the CAN diagnostics...

'Diagnostic access via CAN is not possible on the 1M model, and it's also unnecessary.'

Just look at the measurement data blocks on channel 125... you'll see that the CAN bus is active, just like with you.

All vehicles within the Volkswagen Group received the Motor CAN system in May 1999 (model year 2000), and it was further expanded again in May 2001.

Just look at the measurement data blocks on channel 125... you'll see that the CAN bus is active, just like with me.

All vehicles within the VAG group received the MotorCAN system in 5/99 (MJ00)...and it was expanded again in 5/01!

I agree with you completely; my system is configured the same way. However, the MSG unit doesn't care what settings are in the AI (Artificial Intelligence) module. If there's no CAN hardware on the MSG, then no CAN data will be received.

I find it possible that YOUR specific PD has a CAN bus, but as I said, this still needs to be verified!

MY ASV definitely doesn't have one! Don't generalize about things you haven't verified!

Very important:
The diagnosis is performed via the K-line, which operates independently of any CAN bus system.
If she tells you there's a CAN bus, it might not be true, as they are separate buses.
You can only know for sure if you actually see the signals, measure the levels, and are able to measure the output impedance.

Okay, get your multimeter and just try it. I'll tell you if it's a CAN bus or not.
And believe me, I know what I'm doing; I make a living from it.

Best regards, Jochen.

P.S. I was also disappointed that, despite all the appropriate settings and comparisons with VAG vehicles, the CANalyzer didn't provide any useful information.

Well, since you make your living from this, you've probably opened up the control unit and checked it out. Until May 1999, the circuit boards were only partially equipped with CAN controller chips; after May 1999, they definitely are.

I don't understand why you always associate the diagnosis with the communication between control units... Diagnosis via K-line, communication via CAN.

And if that's not the case for you... then maybe you really do have a Golf 3 underneath your Leon's exterior .

Well, since you make your living with it, you've probably opened up your control unit and checked,...until 5/99, the circuit boards are only partially equipped with CAN controller chips...but definitely from 5/99 onwards.


Right, slowly but surely, the circle is closing .

Just so, it's like that with every VP 37, as long as it doesn't have traction control.
By the way, this is software version 3357. That's probably the simplest thing about it.
Unfortunately, my Leon is a 10-2002 model, and even though it has a VP 37 from 2004, it still uses the same engine control unit!
What you wrote applies to Volkswagen and Audi, but not to SEAT.
They are always 'behind' .


I don't understand why you always associate the diagnosis with the communication between control units... Diagnosis via K-line, communication via CAN.


Where am I messing things up?
Perhaps you didn't read it correctly, but I am clearly stating that the diagnosis is done via the K-line, and that the CAN bus doesn't actually know anything about it; these are separate buses that exchange values during some kind of programming. If someone says there's a CAN bus present, the diagnostic system believes it, even if it's incorrect.
K-Line is also a communication bus, but with a different physical layer. VAG-Com actively communicates with the control units and even switches protocols in the process.
The CAN bus can more accurately be described as a 'passive' communication system, meaning it's not a 'question and answer' type of interaction.

Furthermore, the graphic on Seat-Leon.de is quite amusing. There isn't a real 'infotainment CAN' system. The communication between components like the infotainment system, phone, and navigation relies on MOST (Media Oriented Systems Transport), which is an optical bus. A CAN bus would be far too slow for that purpose.

'No one agrees that the CAN bus is present in the wiring diagrams, as I have already mentioned. However, I have also verified that these cables are not needed. Therefore, there is no evidence of a CAN bus!'


And if that's not the case for you... then maybe you really do have a Golf 3 underneath your Leon's exterior .

Yes, I already mentioned that in my first response.

Best regards, Jochen.

Jochen_145 wrote:

K-Line is also a communication bus, but with a different physical layer. VAG-Com actively communicates with the control units and even switches the protocol during this process.

As long as it's correct, the focus is on establishing communication using a specific protocol rather than frequent switching between protocols. Protocol changes (e.g., from KWP-1281 to KWP-2000) then become less common.

Jochen_145 wrote:

It's more accurate to describe CAN as a "passive" communication system, meaning it's not a "question and answer" type of interaction.

You are mistaken here. The diagnosis runs on a separate CAN diagnostic bus (except for Audi A4 (8E)). This bus is chronically inactive until the diagnostic device initiates communication. Then, and only then, data can be found on this bus, but even this data is only available upon explicit request, not as a general "broadcast."

Jochen_145 wrote:

Furthermore, the graphic is already funny on Seat-Leon.de. There isn't really an infotainment CAN bus. The communication between components like the radio, navigation system, etc., uses a MOST (Media Oriented Systems Transport) bus, which is an optical bus. A CAN bus would be far too slow for that...

Here, I definitely have to disagree with you. As you correctly stated, MOST is an optical bus, but it's only used in the Audi A6 (4F), Audi A8 (4E), and Audi Q7 (4L) models. All other VW/Audi models (e.g., Phaeton/Touareg/Passat/Golf/A3/A4, etc.) have a CAN-based infotainment system.

As long as it's correct, the approach involves establishing communication through a specific protocol rather than frequent switching between protocols – protocol changes (e.g., from KWP-1281 to KWP-2000) then become relatively rare.


That's exactly what I meant by switching the protocol in VAG-Com.
The individual control units are accessed using different protocols.


You are mistaken here. The diagnosis runs on a separate CAN diagnostic bus (except for Audi A4 (8E)). This bus is chronically inactive until the diagnostic device initiates communication. Then, and only then, data can be found on this bus, but even this data is only available upon explicit request, not as a general 'broadcast.'

See, that's not a classic CAN but rather CCP (CAN Calibration Protocol). It's a protocol built on top of CAN. It's commonly used for diagnostics over CAN.
CCP is theoretically similar to KWP2000 or the like, but instead of using a specific physical layer, it utilizes the physical layer of the CAN bus. The communication takes place within the 8 data bytes of the CAN message. This approach is used by (almost) all manufacturers who do not expose the CAN bus directly.
Bei VAG ist erschwerend noch, dass die CAN-Leitung aktiv zugeschaltet wird, damit die Pegel an der OBD Dose liegen. You are right.

A CAN bus is a passive bus that only requires an acknowledgment as a response. It transmits data regardless of who is listening or interested. Furthermore, it doesn't matter which device sends the response, unlike in the case of CCP. This is the specification of the CAN bus!


Furthermore, the graphic is already funny on Seat-Leon.de. There isn't really an infotainment CAN bus. The communication between components like the radio, navigation system, etc., uses a MOST (Media Oriented Systems Transport) bus, which is an optical bus. A CAN bus would be far too slow for that...

Here, I definitely have to disagree with you. MOST, as you correctly stated, is an optical bus, but it is only used in the Audi A6 (4F), Audi A8 (4E), and Audi Q7 (4L) models. All other VW/Audi models (e.g., Phaeton/Touareg/Passat/Golf/A3/A4, etc.) have a CAN-based infotainment system.

It's strange that I found the MOST bus in the Touareg, the Phaeton (which is very similar to the Audi A, and in the Audi B6 and Audi B7 (Audi A4). I have even deactivated it (unplugged it) and received the corresponding results (no radio, error message).
These vehicles were production models!

Best regards, Jochen.

Jochen_145 wrote:

That's exactly what I meant by switching protocols in VAG-Com. The individual control units are accessed using different protocols.

I think we're talking past each other. Communication is initiated, let's say using the KWP-1281 protocol, then diagnosis is completed, and the connection goes "dead." A new communication attempt is made, perhaps using KWP-2000, diagnosis is completed, and again the connection goes "dead." A "switch" occurs when the protocol changes during the communication process; anything else isn't really a switch in the true sense.

Jochen_145 wrote:

It's strange that I found the MOST interface in the Touareg, the Phaeton (which is very similar to the Audi A, the Audi B6 and Audi B7 (Audi A4), and that I have even deactivated it (unplugged it) and received the corresponding results (no radio, error message). These were all factory-standard vehicles!

Okay, then tell me where you found mold on the Touareg, Phaeton, or A4 (8EC/8ED/B7). I'll go check it out myself, and then we can talk more about it.