Electrics: 70: Diag issues - 1/2 of the car will not communicate

[Foxik]

Hello,

I will start with a little disclaimer - it is my first post, not just here, but on forums in general. I hope that I did everything right (right category etc.), if not, please let me know - I will try to fix it.
+ Pardon my imperfect English.

Now to the problem itself:

"Introduction":
In my country, we have car state inspections. My V70 is due for one.
My SRS light is on, and, because of my stupidity doing brakes, the ABS light is on as well, thus I have a great start for state inspection...
I do not want to take out DIM lights, I want to fix the issue(s).

The issue:
The first big one was to realise that V70 I (1998) is in the perfect years of 1996-1998, so OBD-II is not OBD-II, and the old Flash codes are no longer here.
Thus I bought VAG-KKL, later VAG-CAN-K cable, got myself VOL-FCR and VAG commander and tried to diagnose the DTC, and erase them.

Now the "fun part" - half of the car does not want to communicate.

Engine, immobiliser, clima-module works fine - I can speak to them, I see the live data and work with DTCs.

SRS module - I can communicate with it, after making the connection and asking for DTC I got "faulty data", live data are not readable (? instead of data).

ABS module, DIM, and few other modules are not responding.

Now "the well" where I have fallen:
I have spent about 30 hours trying to solve it, diagnose it, fix the issue.
I will write here everything I have done that I remember.

I asked on the local Facebook site for help, only answer I got was to check the solder on the pins on the ABS module.
So I did - pins were fine, I did resolder them, to be sure.
I did the same for DIM. I have seen some old fixes in DIM where the heat sink rubbed the PCB. I did checked these places with DMM and put lacker over them to be extra sure. Because the DIM works as it should (beside the com issue), I do not think it is damaged.

During my poking into these modules, I did find CAN transceiver chips and traced them to pins on the connectors. I did hooked CAN-Hi, CAN-LO vs. GND on the oscilloscope. When I was with probes behind DIM, with ABS disconnected, I did see sync pulses. When I connected it to ABS, I did see data transfer. I did usu DMM to check voltage at CAN-Hi and LOW - both are about 2,5 V. Thus this part of CAN must be fine. But it seems that DIM CAN is only connected to ABS module. I could not find any info if this is OK, or not.

I did put probes and DMM at OBD-II port and it was silent - no CAN signal.
From what I could find on the internet it goes straight to CEM - I do not know, if there is some active safety decoupling of the OBD-II port vs. the car, or some transceiver/signal converter.
CEM is hidden so well that I can´t reach it.
So I did the risky thing and connected CAN behind DIM with OBD-II CAN (bypass CEM). I can now see CAN voltage at the port but the com issue is still present - nothing has changed in any way.

I did find that a typical CAN has 2 terminating resistors on both ends. I tried to measure them, but I have not measured any ohms between CAN lines at ABS and OBD-II. Thus I assumed this car (maybe cars in general) does not have any. Does cars, especially V70 I have CAN line resistors? If so, where are they?

I did check many things visually, but everything seems to be OK.

Internet is silent about similar issues, Chat GTP had gave a lot of info about CAN, K-Line and OBD-II coms, but I still don´t know what should I do next.

I could not find a definitive answer if Vida DICE will work on this car. It is pricy and and do not want to buy it just to try it. + I personally thing that I will not work.


"The question":

So, is here anybody, who can point me in the right direction? I need my car on the road, and these issues taken care of.
It´s sad, but You are my only hope - I do not where else to ask, or what to do next.

[Martin Cox]

Firstly welcome to the forum. Secondly, yes you have posted in the right part of the forum for your car.

I too have a 1998 V70 and as you correctly say these cars are not fully OBD2 compliant. I don't think Vida will help either.

The 850OBD2 app for android phone together with a suitable ELM327 dongle should work. it has the advantage of being cheap. For me it can read ABS codes and will connect for live data.

Presumably the ABS fault light did not come on before you did work on the brakes. If this is true then something has happened to upset the system. I'd check for faulty connectors, damaged cables, corroded or disintegrating reluctor rings or faulty sensors. Take a careful look at anything else that may have been disturbed whilst workiong on the brakes.

I can't advise on the SRS system since I have no experience of it.

Martin

1998 V70 Tdi auto

[Baffler]

Originally Posted by Martin Cox

The 850OBD2 app for android phone together with a suitable ELM327 dongle should work. it has the advantage of being cheap. For me it can read ABS codes and will connect for live data.

Agree with Martin here as the Android app and dongle can be bought for ~€20 so definitely worth a try. Just be aware some of the cheaper dongles can fail to communicate, buy from a reputable seller so you have some comeback/support.

You could be having comms issues with the VAG cable/interface. These things are mass produced, as the dongles are, so can be hit and miss depending on what day of the week they were manufactured

Also, is your VOL-FCR from ilexa? Free version may not have certain functions activated.

[Foxik]

Originally Posted by Martin Cox

Firstly welcome to the forum. Secondly, yes you have posted in the right part of the forum for your car.

I too have a 1998 V70 and as you correctly say these cars are not fully OBD2 compliant. I don't think Vida will help either.

The 850OBD2 app for android phone together with a suitable ELM327 dongle should work. it has the advantage of being cheap. For me it can read ABS codes and will connect for live data.

Presumably the ABS fault light did not come on before you did work on the brakes. If this is true then something has happened to upset the system. I'd check for faulty connectors, damaged cables, corroded or disintegrating reluctor rings or faulty sensors. Take a careful look at anything else that may have been disturbed whilst workiong on the brakes.

I can't advise on the SRS system since I have no experience of it.

Martin

1998 V70 Tdi auto

Thanks for the reply. I am happy, that I am here correctly!

850OBD2 app is something I can try - this is the first time I have heard about it.
I do own Vgate iCar2 - presumably EM327, thus it should work with it. I will try it and let You know.
I did try about 3 OBD-II apps with no luck - presumably because it is not exactly OBD-II...


ABS is surely my fault.
About 10 years ago (judging by the rust) somebody was doing brakes on my car and broke one of 2 rear calliper screws.
To fix it I needed to weld a nut on the remainder of the bolt.
I could not reach it normally (when the hub was still on the car), but undoing the 4 inner hex screws was almost impossible, so I did cut a few of them - doing it my angle grinder slipped right through the ABS sensor cable. I did fix it, but the code is still there I assume - worst case scenario - buy a new set of ABS sensors.
The light came on right after me being handy with the grinder.
That´s a gift I got for being lazy...

I did hear that a battery under voltage can cause SRS code - that this module has some construction fault and likes to write false code when the battery is low.
If the app suggested by You will not work, I will try a diagnostic when on the charger.

[Foxik]

Originally Posted by Baffler

Agree with Martin here as the Android app and dongle can be bought for ~€20 so definitely worth a try. Just be aware some of the cheaper dongles can fail to communicate, buy from a reputable seller so you have some comeback/support.

You could be having comms issues with the VAG cable/interface. These things are mass produced, as the dongles are, so can be hit and miss depending on what day of the week they were manufactured

Also, is your VOL-FCR from ilexa? Free version may not have certain functions activated.

I will try the dongle with the app suggested by Martin and let You folks know.

I did check the internals of the cables. They seem to be fine. But yes - what do I know if they are OK? My dad has the same car but the year 2000, thus fully OBD-II compliant. I can try it there to see if the cables work or not.
I did try the dongle with the OBD-II app there and I managed to get some info back.

The issue is that I do not know for sure which line the ABS, DIM and SRS modules use for outer coms to "OBD-II". K-line seems to be fine - signal-wise and even coms-wise using the cable. CAN is suspicious to me - the reasons are written in the original post.

[Foxik]

Originally Posted by Foxik

I will try the dongle with the app suggested by Martin and let You folks know.

I did check the internals of the cables. They seem to be fine. But yes - what do I know if they are OK? My dad has the same car but the year 2000, thus fully OBD-II compliant. I can try it there to see if the cables work or not.
I did try the dongle with the OBD-II app there and I managed to get some info back.

The issue is that I do not know for sure which line the ABS, DIM and SRS modules use for outer coms to "OBD-II". K-line seems to be fine - signal-wise and even coms-wise using the cable. CAN is suspicious to me - the reasons are written in the original post.

Quick update - I bought the app, but it will not communicate with my dongle. I did order another one - will be here tomorrow - I hope. My fingers are still crossed...

[4x4]

This one will work Click

[Foxik]

Originally Posted by 4x4

This one will work Click

Thanks for the suggestion!

I got one dongle working ("We do it right because we do it thrice...").
SRS is now communicating. DIM and ABS are still silent... Even with the CAN jumped from DIM to OBD-II.
I tried to unplug DIM, to test ABS, but ABS is still silent.

I am suspicious of one of these modules, especially the ABS.
I will look on the CAN waveforms, I did save them on the scope. The CAN voltages are low, but the CAN still seems to work.
My current thoughts are that one of the CAN chips is faulty and brings the CAN voltage low.
______
Update after analysing saved waveforms from the scope:
The CAN is moving from 0-1 V (Hi) and 0 - -1 V CAN LOW

the transceivers are
https://html.alldatasheet.com/html-p...6/A82C250.html
Both in the DIM and ABS modules.

The datasheet specifies that the output voltage should be like in traditional CAN - 2,5-3,5 V (Hi) and 2,5-1,5 V (Lo). Thus seeing voltages moving around 0 V, not 2,5 V, although the 2 V difference between CAN is OK can be the issue.
Funny enough - I am starting to think that these transceivers are so tolerant (according to the datasheet spec.) to voltage faults that they can communicate between themselves - thus I can see CAN coms, but the Dongle can not communicate, because it is looking and communicating in traditional CAN around 2,5 V.
We might be looking at a shot transceiver. Hopefully not dead driving logic - I can't bench test it (I think).

I will check the car with scope again, and I will try to narrow the fault to the exact module, so I can check it on the bench...