Any CAN experts here? auto electricians...?

[s31len]

Bit of a longshot here, anyone one here knowledgeable on CAN bus workings?

 

[Da]

What do you need to know? There's alot of guides and info on here that may help.

 

[s31len]

Its quite a technical question, but ill post up incase anyone cleverer than myself reads it

Basically, got a problem on high speed can, i believe it to be the engine control module, is pulling down the network (as this is and the instrument pack is the master modules)

After some possible ideas as to why. the two master modules on the can lines have an internal resistance of 120ohms, should this be only when the modules have power, or permenantly? i.e before all modules test network integrity, will they need to be powered up?


As i said longshot, but maybe some techies on here, or electrical engineers dealing in the type of thing.

 

[Da]

Hmmm, way over my head but I hope someone can help you!

 

[barnesautos]

The resistance of the circuit is measured with the control units not fitted normally the resistor is in the control unit itself Engine ecu and/or can block. when resistance is measured with the Ecu fitted the resistance is halved as its then a running a series circuit. say 120ohms not connected and 60ohms all connected.
Hope this helps.
What problems are you having

 

[s31len]

Way i understood can, if i was to measure resistance across two pins of a module NOT a master, for a complete network id expect 60ohms, if 120ohms means a fault with one of the masters, (or open circuit a fault such as cut wire)

Problem is having repaired a car, programmed the affected modules, had it running no problem, then switched off and left, go back to it, ignition on and all modules on the HS can are down (dash light up like a christmas tree), plugging into diagnostics all modules report lost comms with ECM.

To get it back up and running, have to leave the battery off to hard reset, clear DTCs, then not a problem, until left and tried again.


Basically, the ECM is not responding/transmitting when ignition first turned on, but why its doing this i have no idea....any ideas?

 

[barnesautos]

Which module have you programmed first? also is the christmas lights the only problem.
Or are experiencing non start aswell. or is that can back up and running

 

[s31len]

engine control module.

the christmas lights/non start is the effects, the problem is that when i put the ignition on, the can network falls over, and needs hard reset and dtcs clearing to get it back up and running if that makes sense

 

[barnesautos]

Ok have you measured the voltage of the can high and low = should be roughly 5volts when added together ie high 2.85v low 2.18v.

If so measure the volts when system is ok and make a note.

Then measure the high can when dead. if its considerably lower or even no volts at all pull of the cluster and see if the volts wakes up.

Have you tried leaving the motor to go too sleep with the cluster disconnected? and then check for the fault again. let me know how you get on

 

[s31len]

ill try these tomorrow and let you know mate, thanks for the help.

to measure can voltage, am i remove a module and to measure can wire to ground yes?

i havent disconnected the cluster at all yet, no. will look at this tomorrow.


i could capture a can trace of both conditions (in theory), im guessing this could show if it is a missing can signal - and which module yes?