I really don’t think I can help you anymore but since you are not reading 60 ohms on your Expansion Bus further electrical diagnostics will be needed…at least you have something to start with there.

 

Sure, next week hopefully the new differential carrier will arrive and the car will be brought to my Mechanic (which i will give the wiring diagram you kindly sent me to find the short).
will update you once i will have news, for the moment, thank you so much for the amazing help and all those extremely helpful information.
i really appreciate it.

 

Hi, i did the test you told me yesterday.

With battery disconnected, i went and check the resistance between Pin 12 and negative on a grounded chassis bolt of the door, same with Pin 13.
in both case the result was "OL".

one question, seen that apparently i have a short on the CAN line (zero resistance between Pin 12 and 13) is it normal to have a perfectly normal voltage of 2,6V on both of the Pin?
how can it happen if they are shorted?

ALSO:

I did this test aswell today:
(All perfromed with Battery disconnected)

1- unplugging the Rear Differential Clutch Module and checking for the resistance in DLC port 12, 13.
Always "0" result.

2- unplugging the Chassis Control Module and checking for the resistance in DLC port 12, 13.
Always "0" result.

3- unplugging the Electric Brake Control Module and checking for the resistance in DLC port 12, 13.
Always "0" result.

Note: i know that the CCM and EBCM are not giving my "no communication" issue, but as i had DTC related to them, i tested the same.

I STILL NEED TO TEST THE "SWASM"
(Steering Wheel Angle Sensor Module) that together the RCCM results not communicating, i have to fugure out where it is located.
i guess behind the steering wheel?
or on the steering colum?


thanks

 

You said earlier you had 0 ohms or “continuity” between 12 and 13 so the CAN lines are shorted together somewhere…don’t know what else to tell you and it would be impossible for me to guide you step by step in your diagnosis…looking at your amp clamp it could also be you have faulty leads or the amp clamp…I have never heard of that brand…if you show OL between either pin 12 or 13 the CAN lines are not shorted to ground but shorted to each other.

 

Maybe i wasn't clear in explaining myself.

If with battery disconnected, i check the resistance between 12 and 13 i have "0 Ohms".

if i do the test you asked me, always with battery disconnected and I put the Red lead on pin 12 and the black lead on a chassis bolt (door) i have "OL".
same thing happens if I do the test with Pin 13.

I never said to have "OL" between 12 and 13, those give "0" resistance eachothers.

if you had the chance to read in full my previous message, I stated that I've tested disconnecting the CCM (always having 0 resistance between 12 and 13) and this the same with EBCM and RDCCM, same results, i did the test to check if one of the above-mentioned modules were the problem, apparently not as the result is always 0 tension with/without them plugged.

Now, my question was, is it possible that I have zero tension between 12 and 13, while (with battery and ACC on) having a perfectly.good 2,6V?

 

When you measure 0 ohms you have an open not a short.

Some meters OL indicates either and open or a out of range on non auto ranging meters.

 

An open should read 120 ohms, not zero.
a short read zero.

 

Yes, between 12 and 13 should read 120 ohms IF NOT SHORTED TO EACH OTHER !!..if you read 0 ohms they are shorted to EACH OTHER !!

 

First picture depending on your DVOM with an open you will see either 1 or OL as on the Fluke…2nd picture you have continuity so you subtract the resistance of the leads…subtract .2 on the left and .1 on the Fluke…
3rd picture if you have 0 ohms or continuity the CAN wires are shorted together…pin 12 or 13 to ground OL means they are not shorted to ground but instead to each other…this resistance check is just a check of the “physical layer” as it’s called…ie…the wiring…I’m tapping out !!…maybe another member can offer some advise !!…know and TRUST your equipment !!

 

Got it, thanks for explaining again.

As far my question:

1- the test i did of removing one by one the modules and testing the resistance between Pin 12 and 13 that remained "0", means the the short (between the two canbus wires) isn't inside any of the modules? Otherwise removing the "shorted" module would bring the resistance back to 60 Ohms right?

2- moreover, assuming i have the 2 can wires shorted to each other, is normal that with battery conncted and ACC on having a perfectly fine value of 2,6v?

 

Even with the CAN wires shorted together you would still see around the differential voltage of 2.5 volts…my suggestion to you is disconnect the Steering Wheel Angle Sensor and probe pins 1 and 3…you are checking the wiring back towards the DLC…if there is NO short you would now see 120 ohms being that the 120 ohm resistor is in the Airbag Module…now this would mean the shorted wires are downstream going towards the EBCM…you need to look at the pin numbers and follow it until the short disappears !!..those lines going across the wires means those wires are a “twisted pair”..they twist the wires together to reduce RF !!

 

Thanks for the hint!
so the Steering Wheel Angle Sensor Module is the on behind the steering wheel (the also called Clock Spring) and not the modules mounted on the steering rack to power the steering wheel right?

 

Yes, commonly called the “clock spring” and technically it’s not a module as would be the ECM and EBCM etc…#7 in diagram.

 

Do you have access to Service Info in your country such as Alldata or Mitchell ??

 

thank you again, too bad i am not able to access Alldata (yet i tried) because it says is unavailable in my country, that would be plenty of help... wish I could buy the access aswell.

 

You can try GM…I believe they have service info for maybe 3 days or so…you can check that….ciao !!

 

Going to try, thanks and Ciao 😄

 

BTW, you really should be using a lab scope for CAN bus diagnostics…that 2.5 volts we were talking about CAN high goes from 2.5 up to 3.5 volts and CAN low goes from 2.5 to 1.5 volts and the waveforms mirror each other…voltage and resistance are only 2 quick methods to see if you may have a problem..the top green waveform is the Low Speed or Serial Data Network…it produces a 0-7 volt square wave…these signals are EXTREMELY fast and is measured in millionths of a second (Microseconds).

 

Hi
Today we checked that my OBD2 port had been mounted back in the past upside down, so I was checking wrong PIN.
Now I checked the correct PIN (12 and 13) and i actually have 120 ohms.

the wiring has been checked, looks fine.
but we see 120 ohms on the EBCM and Airbag (seen that they both have 120 ohms resistance right?) How can we see 60 ohms if they have such resistance?

As told the wiring has been checked by the electrician and told me it's fine.

thanks

 

Checking the wrong pins could have really set you down the wrong path !!!….If you are seeing 120 ohms on 12-13 the wiring is NOT fine...you have a broken wire or module somewhere...you read 60 ohms because 2 (Airbag and EBCM) each 120 ohm resistors WIRED IN PARALLEL EQUALS 60 OHMS...what you need to do is split the bus in half to see where the break is...disconnect the chassis control module connector and now jump pins 2 to pin 5...now go and check the resistance at 12 and 13 at the DLC...if you read 120 ohms the break is not from the chassis module back to the DLC...now take your ohm meter and go from pins 3 to 4....if there is a break in the wire between the chassis module and the EBCM you will read an OPEN with the ohm meter...understand what we are trying to do here ????...sorry but I think this diagnosis may be a little over your mechanics head and you need a shop that only works on car electrical systems…this can also be a break in the circuit for that module also…BTW, communication wire are always next to each other on a connector and are called a “twisted pair” because each of the 2 wires are twisted together…what you can also do is disconnect each module and jumper the wires going in and out of the module and see if 60 ohms returns…this depends if the bus wiring is ok…this will not be easy.