Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
Discovery 3, CANBUS mean voltage.
Hello All. My first technical post here.
Lets make long story short; after 6 months and couple of different workshoops my Disco 3 2008 in unusable. Started as HDC fault, lights radio of hazzard blinking. After repairment stuck in limp mode permanently. i brought it home, ordered Iidtool and started. apparently there is only one permanent error that i was woried about and that is U0101-87 (2F) Lost comunication with transmition control module (TCM), bus sugnal message failure-missing a message.
Rechecked:
- contacts integrated transfer unit - OK (visual)
- Voltage on TCM (gearbox plug) OK
- Ground on TCM (gearbox plug) OK
- Canbus resistance on TCM 60.1O OK
- Check for shorting different wires on plug when shifter unit is disconected on plug near to CJB all OK.
Measured Canbus voltage with multimeter when ignition on and engine not working. Mean canbus voltage on TCM plug.
CAN high to ground 2.52V
CAN low to ground 2.31V
Measured resistance between Canbus and ground when battery disconected.
CAN high to ground approx. 1.5kO
CAN low to ground approx. 1.5kO
Rechecked voltage at ODB connector. Same readings. Any ideas ?
I have some toughts but would like to hear yours.
best regards arno
29th Jan 2021 1:56 pm
N5Fav
Member Since: 28 Jan 2021
Location: LEICESTER
Posts: 134
Sorry,
But you can't check CAN like that.
Can signals are square wave form, so you need to measure them with an oscilloscope.
High CAN and Low CAN are mirror images of each other and are switching very fast.
Most CAN problems are bad connections, or possibly a broken wire - CAN wires are quite thin.
But measuring with a multimeter is a waste of time
Hope that helps a little
29th Jan 2021 3:48 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10726
i think resistance checks are a valid thing to do.
As well as check for continuity between modules (i.e the wiring is ok)
29th Jan 2021 4:02 pm
N5Fav
Member Since: 28 Jan 2021
Location: LEICESTER
Posts: 134
Resistance checks OK, but measuring voltage has no real benefit.
I've known on Fords that a faulty ABS pump can upset the CAN system and knock out the immobiliser system, so CAN faults are sometimes a real pain to track down, the wiring can be good, but a faulty component elsewhere can upset the CAN signal to something else.
I found the ABS fault by just disconnecting everything one by one until I had communications back.
Electrics can be a nightmare
29th Jan 2021 4:08 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10726
sometimes it can be the twisted yellow wires under the rear of the car on the left.
or its more likely to be water in the fusebox
29th Jan 2021 4:15 pm
Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
I agree with everithing that has been said,but measurment of mean voltage is probably shoving distorsion in voltage signal on CANBUS high wire since the mean voltage is significant lover value than expected. It is measured 2.51V what is almost idle voltage. Further on threr is no distorsion in resistance measurments when canbus is on sleep; that means when transreceivers are asleep there is no isues i.e. canbus is healty. As well there are no issues in the wireing beside canbus or maybe there is but when we found out which module is failing.
Now there is only question how to rule out modules on canbus and see when mean voltage will come to tolerance. When the mean value of the High can and Low can will be 2.5V that means we probably have simetric signal.
My question is now how to do that, and i see two ways:1. Removing the Ecus from network, not easy and probably not possible for me at the moment. 2. Removing power suply from certain ECU-s, Do you agree?
Aprechiate any comments. arno
29th Jan 2021 5:35 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10726
It’s common to get these no comms network message s
I would try and figure out by clearing and reading quickly if it comes back soon
And also check gearbox functionality.
Does it come out of park
Do the reverse lights work
Does the gear box dash displays work.
I’d check the gearbox fuse and power at the gearbox
Then back to the wiring diagrams to see where cans wires run
Also search for other threads on here for “flashing hazards”
29th Jan 2021 6:19 pm
Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
Thanks Pete,
It is permanent message, not possible to clear. Gearbox is at not comunicating at all, power, canbus, ground ok on TCM plug. No live data visible nothing, therefore i beleive it is not gearbox issue. What i found out from mechanic is that they initially in search form "flashing error" they tryed to flash TCM and after that vehicle went in permanent limp mode, apparently i delivered vehicle only with comng and going "System shuting down" issue never had any gearbox related issues, i beleive gearbox is colateral since they tryed to reflash on "bad" network. Reading of the mean CANBUS voltage is without TCM on netvork to rule out that component.
29th Jan 2021 6:40 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10726
They bricked the gearbox did they ?
If you give gap your vin, they can give you a file to reflash it.
Connect a battery charger power supply though
29th Jan 2021 7:15 pm
Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
I think so but not sure. From my understanding if there is a initial problem with CAN what caused flash failiure that needs to be addresed before sorting out TCM.
Update:
I did a little bit of testing,troubleshouting and measuring with my primitive multimeter. Disconected power supply from cluster unit which I had a gut feeling is troublemaker on CANBUS. And both mean values of CAN high to ground and CAN low to ground changed for approx 0.3V. hazzard lights flashed and had multiple locking and unlocking he doors, obviusly can is signal corrupted and and car goes to sutting down mode.
Tomorrow i am picking up cluster and will try to hook it up with my car. I beleive that should work on network as it should even though is not synked to my car. Will try to pick up voltage values with multimeter
Could somebody comment on that; transreceiver will sink with netvork in order to pick up data?
29th Jan 2021 8:24 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10726
Imboliser code in instruments
So it won’t start with different dash.
May learn something or have 2 cars that don’t work
29th Jan 2021 11:04 pm
Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
But cluster will transreceive data that i can pick up.
If another cluster is cure it will stabilize signal and mean voltage will rise in expected values. Then I can synk it with my car with Iidtool.
If I remember from when I worked at JLR, the immobiliser is in the key and is stored in the ECM (Engine Control Module). The remote key fob used to unlock the doors is stored in the BCM behind the glovebox.
Have you checked the terminals on the transfer box ecu in the battery box? They are notorious for corrosion on the terminals.
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!
29th Jan 2021 11:48 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10726
Good point about ecu pins
Imboliser code stored in 2 places
30th Jan 2021 12:24 am
Noar
Member Since: 18 Mar 2019
Location: Åesund More og Romsdal County, Norway
Posts: 25
Yes, those terminals checked and cleaned. I am not so much considered that this is wiring issue, since reading of the resistance when canbus asleep is ok. (60.1ohm) that is main spine, branches will not affect and will result as only one unit with comunication issues. I am more woried about canbus transducer on one of the modules. From shematic i found out that integrated transfer unit is bridging spine of te cambus and therefore if connection problem there it reflect to whole signal. At least that is my understanding.
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that means we probably have simetric signal.
