BCU to IDM serial link

hi all - I don’t suppose anyone has a scope trace of a healthy BCU to IDM serial link they could share or a description of what it should look like?
Mine appears to be erratic - I cannot seem to capture a clean trace with a normal serial trace. This might be me not being used to a new pc based scope with a crappy interface but I would like to check before condemning anything.
Also when switching a circuit on that relies on the serial link, should you expect to see a change in the serial link trace when the button is pressed - such as heated rear screen, fog lights etc?
Many thanks to anyone willing to share info.
Matt

I dont really understand what you mean cos it seems you overcomplicate a simple ting... that serial link is a wire, if it has continuity with no resistance it's ok, simple as that, no need to check waveforms on it cos if it's about data corruption the link can't be blamed

sierrafery said:

I dont really understand what you mean cos it seems you overcomplicate a simple ting... that serial link is a wire, if it has continuity with no resistance it's ok, simple as that, no need to check waveforms on it cos if it's about data corruption the link can't be blamed

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Hi Sierra - Thanks for taking the time to reply mate
The link is there and ok as far as I can tell but the IDM is not responding to some commands from the BCU or the commands are not being generated by the BCU for switching on the front and rear fog lamps and the heated rear window.
All the switches bell out to the BCU. Again as far as I have found so far all the wiring seems to be intact and bells out with zero resistance.
I have replaced the IDM from another vehicle and the exact same faults persist.
I am trying to see if the BCU has an internal fault before going to to expense of getting it back to Callrova or another one bought and reprogrammed.
The immobiliser and mileage readings are all ok with no other faults apparent

Harrymattson said:

I am trying to see if the BCU has an internal fault before going to to expense of getting it back to Callrova or another one bought and reprogrammed.

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If the IDM was ruled out IMO the only way to rule out 100% the BCU is to replace it with a known good one, there ar cheap versions on ebay, only a tester is needed to synk it to the vehicle, important is to get it from a reliable seller. From all the symptoms you decribed and if you are convinced that all the circuits of the non worlking systems are OK the BCU is the last suspect... if you live in UK i can recommend you a serious man who can deliver you 100% verified working BCU if you dont want to go for the ebay lottery which can be cheaper but not 100% sure:

Call Paul on
01206 211623 - office
07828 278465
07760 955966
07840 428888

An up date :
Once again thanks for the replies. I have had the fault traced and fixed now. It was a fault between the pcb layers on the BCU beneath some of the components. The BCU was receiving commands but not passing them through to the IDM for action but now all is good thanks to Rick at Callrova.

Nice one