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lynalldiscovery
Member Since: 22 Dec 2009
Location: Maidstone
Posts: 7274
  
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I check can at work using a multimeter, its quick its dirty, but it works.
This is mainly for sensors, 4 wires = 1 power, 1 neg, 2 can.
Neg to can 2.5v ish, then to other can ,voltage much the same means it is good to go and the component itself is faulty.
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 30th Jan 2021 7:03 am |
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Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
 
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Lyna, that is exactly what i am trying.my standpoint is that can high mean voltage and can low mean woltage should be simetrical value around 2.5V. Which will variate a bit but still there should be difference between low and 2.5 and high and 2.5 in approx 0.2V apsolute diference. If that is not the case signal which is out of tolerance is probably corupted.
Update:
Cluster replaced in two hours of observing no System shutin down triggered, but HDC once triggered with lost comunication on steering angle module. . Mean voltages not changed with another cluster laying below 2.5V and dhat gives me idea that whole signal is laying below and idle is below 2.5V due to ground issues, all the whole idea that mean values should be symetric is not valid at all. Will doublecheck ground points according wireing and see is there any visible problems.
At some point during observering read significantly lower voltage both on battery and on dash like a extreme drain somewhere in system. Does anybody have any thoughts about that.
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| 30th Jan 2021 10:30 am |
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Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
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Update: Today conected disco to single chanel pico and measured Can voltages on ODB port, measured both with original cluster and cluster that i borrow. Measurment of the Idle voltages are same and in a range below 2.4V to 2.5V but closer to 2.4V. Since i am not an expert i do not know is this something that i should take care about, obviusly signal is good enough that components are able to send and receive data, even thoght gearbox is not but i beleive it is due to fail reflash. During the testing i cleaned ground points of the cluster but results did not changed.
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| 2nd Feb 2021 1:04 am |
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lynalldiscovery
Member Since: 22 Dec 2009
Location: Maidstone
Posts: 7274
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Ohms, each major componenent will have a resisitor in it, 60ohms rings a bell, 2 = 120 and three = 180, if one part goes tits up it screws the whole lot up, so may have ok volts but not ok ohms.
So I have to assume can conected should be 180, and if you disconnet one part thsu breaking the circuit then depending on which way you measure the wiring you could have 60/60 or 0/120.
Weirdly we never go this deep into the trucks, (if we cannot fit it quick it goes off to the dealer as lack of men/time) but do get tacho faults quite often which is part of the can net and it causes all sort of faults, transmission/susp etc.
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| 2nd Feb 2021 8:26 am |
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TigerRecovery
Member Since: 31 May 2017
Location: Long Stratton, Norwich, Norfolk
Posts: 901
  
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Each bus has two modules with terminating resistors across the CAN wires. The resistance in each module is 120Ohms. As these are configured in parallel it works out at 60ohms when measured across pins 6&14 or 3&11 in the OBD port. If the resistance is higher there’s either a break in the wiring or a module has been removed. 1972 Range Rover Classic 2 door V8
2013 Land Rover Discovery 4 HSE - SCRAPPED
2016 Land Rover Discovery 4 Landmark
2022 Volvo XC40 T5 PHEV 282HP FWD 3 cylinder!
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| 2nd Feb 2021 9:53 am |
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Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
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Guys,
That is sorted out ond is ok 60Ohms. I agree with resistance of the network when modules not powered. What I am trying to figure out is there underlaying issue beside potentially failed cluster and or is there possibility that cluster failed due to intermitent fail of some other transreceivers since with both clusters i read sme discrepancy in idle voltage. There is comunicaton on tetwork since network is designed to compensate that (there is good diferential between can high and can low when sending a impulse).
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| 2nd Feb 2021 10:04 am |
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Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
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UPDATE.
Car is mended now. Cluster swap, programed with great support of GAP team. Gearbox reflashed and finally behaving as should no limp mode.... (car is still on stands but shifting and all live values are visible.) Need a good test ride to se will it trigger system shut down. I hope after 6 months without car,and convincing from mechanics that disco is basket case we are back on truck. 
In proces of analisys and fixing learning curve was steep since nearly ten days ago i did not know anything about canbus and Discos electronic/electric. I can write down my conclusions and if there is somebody who will coment i will apprechiate.
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| 3rd Feb 2021 12:08 am |
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Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
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I see some people, jumped some days ago and said, you can not measure canbus with voltmeter; there is no point to measure voltages between can high and ground and high low and ground. At that time i di not want to comment because I was not 100% sure and did not want to say anything, but it is possible and conclusions that you can draw out of it can be usable to check integrity of the system. Remember mathematical background of Mean values and everything will be perfectly clear, think about that as a ironed signal in specific value somewhere in between idle voltage and idle voltage + amplitude , i know it is not satisficing as it is looking in signal on screen of your oscilloscope, but if you do not understand mean values there is no point to look into signal at all (i am talking about Canbus since there is no specific timing of signal valus, it is just happening in order to transform informations).
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| 5th Feb 2021 10:42 am |
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Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10365
 
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well done for sorting something in 10 days which a garage tried for months 
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| 5th Feb 2021 12:20 pm |
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Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
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Thanks Pete, Apparently system is so robust and simple, for people knowing what they are looking for it should take max half an hour. when hoisting car on stands I barely know what is canbus.
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| 5th Feb 2021 4:14 pm |
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