Skoda Fabia II Can-Bus

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rudolf
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Skoda Fabia II Can-Bus

Post by rudolf »

Greetings,

I keep hitting a wall for almost 2 months now with a 2009 Skoda Fabia II.
The car came in with a lit ABS bulb on the dash, but I could only communicate with the engine.
First thing was to swap the ABS module, then the gateway module, then ecu, then got a donor vehicle, but everything that wasn't working on my fabia, it worked on that and everything that worked on that fabia, didn't work on mine. VCDS shows no communication errors, but I still cannot communicate with anything except engine.
So I started checking the can bus wiring in the engine bay, then moved inside the car, disconnecting modules one at a time and hoping something was interfering, but to no avail.
Below is a can signal capture, but to me it looks fine. the measurement was taken from a breakout box after the obd port.

Any insight is greatly appreciated.
Thank you
Attachments
Skoda_Fabia_2009_Petrol_20240408-0001.psdata
(11.43 MiB) Downloaded 45 times

wiki38andy
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Re: Skoda Fabia II Can-Bus

Post by wiki38andy »

There is no data pack on your CAN signal and wont be so long as scan tool is not connected to DLC port. Scope CAN bus at ECM, ABS, CAN GATEWAY,...and measure at each module the resistance between CAN HI and LOW with battery disconnected(should be around 60/61ohms). Oscilloscope ground MUST be connected to battery negative terminal not to pin4/5 on BOB. Post all the captures here, please. This is how a communication signal should look like.
Attachments
Screenshot 2024-04-08 210433.png

rudolf
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Re: Skoda Fabia II Can-Bus

Post by rudolf »

Resistance is 57 Ohm everywhere.
I made 3 measurements as you asked, I hope this is what you meant. All measurements taken to your specifications on the drivetrain wires. I had a charger attached for the battery, every module connected, key on, engine off.
Attachments
Skoda_Fabia_2009_Petrol_20240409-0001 ABS.psdata
(1.03 MiB) Downloaded 40 times
Skoda_Fabia_2009_Petrol_20240409-0001 ECU.psdata
(1.11 MiB) Downloaded 27 times
Skoda_Fabia_2009_Petrol_20240409-0001 J519.psdata
(1.05 MiB) Downloaded 30 times
Last edited by rudolf on Tue Apr 09, 2024 8:36 am, edited 1 time in total.

rudolf
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Re: Skoda Fabia II Can-Bus

Post by rudolf »

This is the signal measured on an obd plug breakout box, but only with an interface connected. without an interface it sits at 0.
Attachments
Skoda_Fabia_2009_Petrol_20240409-0001 obd plug.psdata
(1.21 MiB) Downloaded 32 times

wiki38andy
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Re: Skoda Fabia II Can-Bus

Post by wiki38andy »

All 3 CAN signals taken from modules look decent to me. There are data packs ending with acknowledge bits(the higher ones), voltage level within the normal ranges. 57ohm between CAN lines is OK. There is no short to ground or power. So, there should be good communication between modules. The packs on OBD signal are all the same and definitely there is no comm/data transfer. It looks like scan tool asks CAN gateway for data, but does not get any answer. Do you have good power on OBD pin 16 and good grounds on pins 4/5? Have you checked the harness continuity between OBD pins 6/14 and CAN gateway connector? All powers and grounds on CAN gateway OK? I would also check these pins for proper tightness.

rudolf
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Re: Skoda Fabia II Can-Bus

Post by rudolf »

There is communication between the modules. They see each other, no communication errors either. The only problem is, that I can't communicate with on can for some reason, only K-line with engine. pins are all OK. Wiring ok, pins ok, continuity ok, modules ok.
I just can't explain it anymore

wiki38andy
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Re: Skoda Fabia II Can-Bus

Post by wiki38andy »

The CAN signal on OBD socket comes from interface. Back probe CAN gateway pins for two wires coming from OBD pins 6/14 to check if you have the same signal from interface. As you have already swapped CAN gateway module there should be a harness/pins issue, only. Nothing to do with any other modules/harnesses. Just focus on this area.

wiki38andy
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Re: Skoda Fabia II Can-Bus

Post by wiki38andy »

Remove pin 7(K line) from OBD socket so as to have CAN comm only with CAN gateway.

rudolf
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Re: Skoda Fabia II Can-Bus

Post by rudolf »

wiki38andy wrote:
Wed Apr 10, 2024 6:48 am
The CAN signal on OBD socket comes from interface. Back probe CAN gateway pins for two wires coming from OBD pins 6/14 to check if you have the same signal from interface. As you have already swapped CAN gateway module there should be a harness/pins issue, only. Nothing to do with any other modules/harnesses. Just focus on this area.
Harness, pins are OK. Everything points to that, but they are fine.

rudolf
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Re: Skoda Fabia II Can-Bus

Post by rudolf »

wiki38andy wrote:
Wed Apr 10, 2024 9:41 pm
Remove pin 7(K line) from OBD socket so as to have CAN comm only with CAN gateway.
there is no can comm. at all
https://ibb.co/K6F5fbr][img]https://i.ibb.co/K6F5fbr/vcds-test.png[/img">

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