CAN BUS Troubles - Jeep JK fitted with Hemi engine

[Littlejohn]

A fault on the interior can would set communication codes in the can c modules as they can’t communicate with the interior modules but would not affect the can c communication itself. All can c modules will continue to communicate with each other with no issues.

[liviu2004]

LED drivers are notorious to induce EMC in electrics. Does not cost you much to give it a try with their wiring disconnected from CANBUS.

[French Chris]

Thanks for your reply Guys.

Next time I get a live Can C fault I will disconnect the front LEDs to see if it makes any difference.

Where about in UK are you John ?

[Littlejohn]

I am in Surrey so not too much of a distance

[French Chris]

Yes I will pm you my details. That would be good to arrange something.

[French Chris]

Hi Guys,

I took some Graphs today and tried to follow the advices of Mr Liviu2004, so I drove the Jeep until the Can Bus fault came back. I then had the ABS, Air Bag, Engine fault, Handbrake lights on in the dash and a loss of Speedometer.

Before connecting my Picoscope I took the resistance measure at the breakout box between Can High and Can Low with Battery Negative disconnected and got 61.2 Ohms,which is correct.

Then I took the resistance between Can High and Chassis Ground at Breakout box and got 19.91Mega Ohms and between Can Low and Chassis Ground 10.00 Mega Ohms.

I took the voltage between Can High and Chassis Ground and got 2.45V and between Can Low and Chassis Ground and got 2.45V.

Now 1st reading at 500ms/div with CAN faults showing stored unfortunately not showing Live on my Scan tool. All modules connected.

2nd reading at 200ms/div with SAS module disconnected.

3rd reading same as above but at 500 us/Div.

4th reading at 500 us/div with ABS module disconnected but SAS reconnected.

5th reading at 500 us/div with ORC module disconnected but ABS and SAS reconnected.

6th reading I tried my luck with Maths channel with ORC still disconnected.

8th reading I tried with Serial decoding with ORC still disconnected.

9th reading which I think is the important one. I disconnected the WRC which has the 120 ohm Termination resistor and the Can High and Low are down to Zero Volt. Then I took the resistance reading at the breakout box between Can High and Can Low and it was still showing 61.2 Ohms. That in my opinion is not right so I took the Can High and Can Low resistance at the WRC connector and got 120 Ohms which is right.

If anyone can make any sens of this please help me.

[kona]

Hello.
You will not RECEIVE any signal from the diagnostic connector by connecting the oscilloscope.
To receive a signal, you need to send a REQUEST.
But the oscillograph cannot send any requests.
Try to connect the scanner and the oscolograph to the diagnostic socket at the SAME time.
And start the divgnosis process. Now you will see the exchange on the diagnostic connector CAN BUS.
BUT IT WILL NOT HELP YOU !

You need to connect to the INNER CAN C BUS. For example, to the ABC connector or wherever it is more convenient for you.
BUT IT WILL NOT HELP YOU ALSO !

Better try unplugging the computer connections one by one and watch when the main problem disappears.

Good luck.

[liviu2004]

I am also puzzled about the diagnostic process. Measuring behind a galvanic isolated gateway, what for.
Second, measure after engine is stopped, battery disconnected, which is like trying to catch a burglar 3h later.

I would keep the scope to the faulty bus with long time base, 1s per division, sample rate crank to max and when problem occurs, stop and save the recording. Then Maybe one can find which can ID makes the trouble.

[French Chris]

Well I am sorry but I don't understand. What's the point for the breakout box then?

Where am I supposed to take the Picoscope readings ?

[kona]

--------------
Where am I supposed to take the Picoscope readings ?

----------------------like this :