Steering column control unit, standalone | Posts 16+

Hello everyone,
I know this thread is really old, but I think this fits in here best.

As part of a university project, I have set up a test rig consisting of a complete steering column assembly with steering column control unit J527 from a 2007 Audi Q7, along with a 12V power supply and a CAN-USB interface.
In the idle state, I measured 3.1V between CAN low and ground at the engine control unit, and 1.9V between CAN high and ground.
Connected are the Can-hi, Can-low, terminal 30, 31, and 15 (which is merged with 30). In addition, the Can-Gnd connection from the interface is connected to terminal 31.

If I run a tracer, nothing happens on the bus with any movement of the steering column switch; in other words, the control unit doesn't send any signals.
When I try to send a message from the PC to the bus, I get a lot of bit errors until the software (Pcan view) goes into the 'Bus Off' state. The errors are 'Data Field', 'Active Error Flag', 'Frame Start', and 'ID.28 to ID.21', and they occur intermittently and sequentially.

The baud rate is set to 500 kbit/s.

'Due to the voltage levels on the Can-Hi and Can-Low lines, I was told that the transceiver may be defective.' After that, I replaced the steering column module, but now I'm seeing the same voltage.
I soldered the connecting cable from a Cat-5e cable, and the bus is terminated with 2 * 120 ohms.


Can someone tell me what I'm doing wrong, or why I'm not receiving any signals from the steering column control unit? Actually, the control unit should also function without the engine control unit, right?
I'm starting to get really desperate, and the deadline is coming up soon.

Thank you very much, and best regards.

Alex.

Quote:

As part of a university project, I have set up a test rig consisting of a complete steering column assembly with steering column control unit J527 from a 2007 Audi Q7, along with a 12V power supply and a CAN-USB interface. In the idle state, I have 3.1V on the CAN drive between CAN low and ground, and 1.9V between CAN high and ground.

What does an oscilloscope display? Are the two levels truly static? Sure about "high" and "low"?

Quote:

The following connections are available: Can-hi, can-low, terminal 30, terminal 31, and terminal 15 (which is merged with terminal 30). In addition, the Can-Gnd connection from the interface is connected to terminal 31. If I run a tracer, nothing happens on the bus with any movement of the steering column switch; in other words, the control unit doesn't send any signals. When I try to send a message from the PC to the bus, I get a lot of bit errors until the software (Pcan view) goes into the "Bus Off" state. The errors are "Data Field", "Active Error Flag", "Frame Start", and "ID.28 to ID.21", and they occur irregularly and sequentially.

What does an oscilloscope display? Do the levels from the top remain static, or are there intermediate stages where you can see that the two drivers are working against each other?

Quote:

The baud rate matches 500 kbit/s.

I'm not an Audi expert. But at VW, there are steering column control units that are connected to both the CAN bus for driving functions and the CAN bus for comfort features - and that operates at 100 kbit/s. Are you sure that this component in the Q7 is only connected to the powertrain CAN bus?

Quote:

Due to the basic voltage levels on Can-Hi and Can-Low, I was told that the transceiver may be defective. After that, I replaced the steering column module, but now I'm seeing the same voltage. I soldered the connecting cable from a Cat-5e cable, and the bus is terminated with 2 * 120 ohms.

I'm assuming that things like SCP-238 and SCP-269 are already familiar.

Quote:

Can someone tell me what I'm doing wrong, or why I'm not receiving any signals from the steering column control unit? Actually, the control unit should also function without the engine control unit, right?

I would say yes, one should watch the broadcasts, but I can't completely rule out the possibility that the device first needs to request a communication channel from Motronic or a similar system.

Quote:

I'm slowly starting to despair, and the deadline is coming up soon.

What does the supervisor say? Or did you choose something where you don't know what you're doing?


Best regards,
Ingo

What does an oscilloscope display? Are the two levels truly static? Sure about high and low?

We haven't connected an oscilloscope yet, as one wasn't readily available. The values were measured using a multimeter. I'm sure about the high and low.

I am not an Audi expert. But at VW, there are steering column control units that are connected to both the CAN bus for driving functions _and_ the CAN bus for comfort features - and that operates at 100 kbit/s. Sure that the part in the Q7 (only) is connected to the powertrain CAN?

Okay, so the control unit has 2 pins for the CAN bus (for driving functions) and 2 pins for the CAN bus (for comfort functions), and they operate at different baud rates (500 and 100, at least that's what I read from the SSP documents).
I'm now only using the pins from the CAN drive.
Yes, the two SSPs are known.

Regarding the bus termination, I previously measured the internal resistance of the control unit between the high and low lines, which was several kOhms. This should be negligible for the bus.

The supervisor doesn't know anything about it either; I think he hasn't looked into CAN very closely. However, since he suggested CAN as a solution even before we started working on it, I had expected something different. 'Nungut' - well, it's not really that important.

Okay, I'll probably try to find an oscilloscope tomorrow morning and then post an update.

Do you have any ideas about what a request for a communication channel might look like?

Thank you for the quick response!!

Best regards, Alex.

Okay, I took some measurements using the oscilloscope directly on the control unit, without using the interface.
Pressing a button has no effect on the measurement signal.

I was able to detect the following signal:

Can-Low switches between 3.5V and 4.2V every 2 microseconds.
The Can-High signal switches from 2.4V to 0.8V every 2 microseconds.
both with a slight overshoot.

I also re-measured the comfort bus (low-speed CAN). I found a static voltage of 10V on CAN-Low and 0.2V on CAN-High.

Attached are the error messages that PCanView displays (for the drive CAN).


While the buses are connected, I haven't measured anything because I would need to remove the insulation somewhere to do so.

Best regards, Alex.

Hello,

Quote:

Do you have any idea what asking for a communication channel might look like?

You're not nearly there yet.

a) Double-check to make sure you're connected to the correct pins, and compare the wiring diagram for the vehicle to see how everything is connected.
b) Try swapping the CAN-H and CAN-L lines.
c) Speculation: The CAN bus timing is controlled by ONE control unit in the vehicle (usually the engine control unit) and the gateway. If both are missing, you must properly terminate the bus, otherwise you will get incorrect data. Fact: Nothing gets done without scheduling.

Best regards, Rainer.

a) Double-check very carefully to ensure you are connected to the correct pins, and compare the wiring diagram of the vehicle to see how everything is connected.

I'm actually quite sure that this will work. Unfortunately, I was unable to find a wiring diagram, but the pin configuration was specified identically in several forums and, ultimately, on an American Audi fan page.

b) For testing purposes, swap the CAN-H and CAN-L lines.
Just to understand: from which information did you gather that this could be a potential problem? As I said, I'm actually quite confident about the wiring.

c) Speculation: The CAN bus termination is located in the vehicle at ONE control unit (usually the engine control unit) and the gateway. If both are missing, you must properly terminate the bus, otherwise you will get garbage data. Fact: Nothing gets done without scheduling.

I normally terminated the connection cable with 2 x 120 Ohms in the connectors. Could that be a problem? I measured 2.43 kΩ between CAN High and Low on the control unit (using a cheap multimeter, so the reading might be slightly inaccurate).

Thank you and best regards,

Alex.