Resistance and Voltage readings for Convenience CAN?

[Owain]

On Convenience CAN should I be expecting 60 Ohm across CAN-H and CAN-L?

On diagnostic connector CAN i see 66 Ohm, which is expected.

Resistance to ground on one line is about 580 Ohm, on other is open circuit.

 

[Dellmassive]

120ohm termination at each end.

66ohm in middle, in circuit.

 

[mmi]

On Convenience CAN should I be expecting 60 Ohm across CAN-H and CAN-L?

On diagnostic connector CAN i see 66 Ohm, which is expected.

Resistance to ground on one line is about 580 Ohm, on other is open circuit.

Have you disconnected the battery? It seems that otherwise the bus is somewhat "alive". I do see approx. 6.2 Volts between convenience CAN-low and CAN-high - however no data going on, just "flat" DC. So, no meaningful resistance measurement available at the moment.

However, powertrain bus is fully down and thus measuring 60 ohms.

 

[Owain]

Have you disconnected the battery? It seems that otherwise the bus is somewhat "alive". I do see approx. 6.2 Volts between convenience CAN-low and CAN-high - however no data going on, just "flat" DC. So, no meaningful resistance measurement available at the moment.

However, powertrain bus is fully down and thus measuring 60 ohms.

I did measurements with IGN off, but battery still connected. VCDS scan shows trailer controller, but comms is sporadic.

I suspect its where I tapped into bus on those big connectors under dash. Probably intermittent.

I shall have to bite bullet and try and get to them again. Bit of nightmare to get to those connectors though.

 

[mmi]

VCDS scan shows trailer controller, but comms is sporadic.

Just the scan?
Have you tried in the VCDS to go into actual Trailer module and set up Adv.Measurements and tick a few items to monitor? This would force VCDS to continuosly poll the module - so then could try to squeeze and twiddle the loom to see if communication gets better, or worse? On that view there is also a communication status available (top left).

 

[Owain]

Finally run tests today. Cleared errors in GW and Trailer module. Entered module, advanced measurements. All worked fine wiggled connections under dash. Went for drive. Still no errors. Scans all clear.

Used "Graph" function. Selected a few options including battery status, Gw, and central electric. Had expected a plotted graph showing errors; dropped missed pa kets etc. Just all a bit confusing/alien. Then i am used to network analysis tools not automotive.

Seems to be all working. Cross fingers...may be debugging this again soon.