CAN-Bus No Com

[Meffi1994]

Hi guys,
I think I have an interesting topic, please bear with me it's my first case study. I am from Germany and translate with a translator, that should be said before.
Back to the topic, a customer brought his 2016 Hyundai Tucson TLe 1,6 T-Gdi to the garage and wanted his engine control unit to be replaced.
The car had previously been to another workshop for diagnostics.
I drove the car inside the workshop and noticed a strange behavior. The engine ran normally, and the car drove without any problems, but all lights and DTCs were blinking on the instrument cluster.
I was wondering, if this will be done by a replacement of the ECU, but the customer definitely wanted it to be replaced, so I did it that way.

As you can imagine, after swapping the engine control unit, the same errors occurred. I connected my scan tool to the car, and was able to read out some DTCs, but I wasn’t able to connect to most of the ECUs.
After informing the customer of the progress, he wanted me to keep working on the car and do a proper diagnosis.

Because my dongle (VCI) had a correct power supply, there had to be something wrong with the communication. I connected my pico to the car and checked Can High and Can Low at the diagnostic connector.

As you can see in the pico files, the Can looked kind of weird.
Since we had some communication on the bus, it was time to check the resistance. At the DLC, I measured 10.1 Ohms between Can High and Can Low.

I was glad to have a track I could follow for now. I now unplugged the engine control unit and the instrument cluster and checked their termination separately. It was in specification (ECU: 123.4 Ohms, instrument cluster: 120.1 Ohms).

So there had to be another faulty control unit. Since the Can signal didn’t have any of the typical error patterns, I didn’t assume a wiring issue. Because of that, I looked up the bus topology and immediately noticed an electronic vacuum pump in the diagram. Since we already had some issues with them, where a part of was Can related, I disconnected the pump and checked the resistance on the bus again. Hah!

We were back in the game with a resistance of 59.3 Ohms. I tried reading out the fault memory and now all ECUs were online and the Can-Bus looks way better. I screenshotted the DTCs and deleted them afterwards. Now I replaced the vacuum pump and measured a resistance of 59.2 Ohms on the Can bus.

Communication is working again, and the car is going back to a happy customer.
Hopefully you enjoyed reading my first case study and maybe it helps one or the other of you.
I appreciate any kind of improvement, suggestions, or feedback.

[Rfmotors1]

Hi Meffi1994,
Very nice case study, thank you for posting.
I have enjoyed reading it and following your diagnostic logical steps. Very educational, it will definitely help all of us here.
Regards,
Roman

[markus281]

Hi Meffi94,

I really enjoyed reading your first case study.
Keep up the good work and of course keep submitting case studies

[liviu2004]

Good one, can diag does not have to be difficult.

[Steve Smith]

Hello and thank you so much for taking the time to create and post your case study as they can take longer to write up than diagnose!

This will most certainly help others and instill confidence when pursuing such faults

The opportunity to graph CAN resistance is now possible with BNC+ scopes thanks to our Resistance lead here
https://www.picoauto.com/products/test- ... -test-lead

Using your technique "Meffi1994" we were able pinpoint the area of concern with this case study very early in the diagnostic process



To save precious time, please watch from 2:48 onwards to view the benefits of graphing resistance

Thank you once again for posting

Take care......Steve

[Meffi1994]

hey guys thank you all for the kind words.

@ steve
Yes, you're right, but unfortunately I didn't think of that at the time. I am also not 100% familiar with the 4425a but I am learning.