CAN circuit test

[aregion]

I am trying to weed out any CAN comm issues on my Armada using simple tests with the multimeter. (from the fact that i have a U1001 on my DTC and other error codes which suggests a CAN issue)

when i test between two point of any component that is connected to the CAN, such as ABS and ECM, I usually get 0ohms between the corresponding connector of the low and high lines. if i test it between terminals from a low CAN line to a high CAN line terminal, i get about 5ohms. this is consistent between all components except when i did a test between ECM and the data link connector.

There is continuity across the low and high line between ECM and data link connector (i.e. 0 ohms and not the 5 ohms).

Is this normal? or is this insignificant information and would tell me if i have a problem with the CAN circuit between ECM and the data link connector?

[Pwnin O'Brien]

Did you recently remove the instrument cluster or do any other modifications to the vehicle?

[aregion]

yes i did remove / reinstall some components on the vehicle including the instrument cluster, but the error codes were there even before and i am sure the were components removed / modified from the previous owner.

my error codes are 1001, 1574, 1212, 0500, which have a common theme of possible CAN line problem. I just want to make sure that the problem is not lying in some silly bad-connector or wiring problem before I send the car again to the workshop. workshops here have a tendency to avoid diagnosing electircal circuit problems and prefer to change parts which doesnt solve the problem and charge you for it.

[Pwnin O'Brien]

My suggestion would be to make sure everything is connected and ensure all wiring harnesses are connected securely. Clear all of the codes (I recommend resetting the ECM) and then see if the codes come back immediately once you start the vehicle after the reset.

[aregion]

ecu has been reset and same problem immediately appears with the same set of codes. rechecked the harness connectors ... not all, but at least where the CAN lines are supposed to go through and they seem ok.

is the 0 ohm continuity I tested across the CAN low and high lines normal?

[Pwnin O'Brien]

You shouldn't be checking for a resistance across the CAN lines, what you need to check for is continuity. You need to see if there is an open circuit or a short circuit in the CAN system. In the factory service manual there is a comprehensive test procedure for the CAN system (look towards the end of EL.pdf). This way you can find where the open/short is and repair or replace the problematic part. Resistance does not indicate continuity.