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CAN wiring and coding for APS+

19K views 10 replies 4 participants last post by  BigP  
#1 · (Edited)
I am trying to retrofit an APS+ to my car that does not have any park assist.

I am done installing the rear sensors, control unit, rear buzzer, and I have wired all cables to the front passenger side. I have made my own cables from a donor car and wired them according to ELSA wiring diagrams.

At this point and since I have wired power, earth, and CAN-BUS to the controller, I expected that the new park assist module would be detected by the car.

I went on coding with VCDS: I added the module Address 10: Park/Steer Assist from the installation list to the CAN gateway module.

However, address 10 is not accessible and I get the following error in the CAN Gateway module:

Address 19: CAN Gateway Labels: 8T0-907-468.clb
Control Module Part Number: 8T0 907 468 H HW: 8T0 907 468 H
Component and/or Version: GW-BEM 5CAN H06 0094
Software Coding: 000303
Work Shop Code: WSC 06325 000 00000
1 Fault Found:

01327 - Control Module for Parking Aid (J446)
004 -- No Signal/Communication
Freeze Frame:
Fault Status: 01100100
Fault Priority: 2
Fault Frequency: 1

It seems that there is either something wrong with the way CAN cables have been wired or the parking module (J791) is faulty (bought it used on ebay). Furthermore I am not sure why the error refers to J446 instead of J791 that is the standard Parking Aid module in a5.

I have tried 2 different wiring methods for the CAN cables.

1. According the the ELSA wiring diagrams (see attached pictures) the CAN wires from J791 follow the exact same path (main wiring harness connections to T17f connector in A pillar and finally to T46s CAN separating connector in dash panel) as the CAN wires from the electric park and handbrake control unit (J540). Thus, I decided to connect the CAN wires from J791 to the CAN wires from J540. This did not work. I even got and error when trying to access the handbrake module J540 and decided not to go this way.

2. I did the wiring suggested by Kufatec in their guide for retrofitting APS+ that I found in another a5oc thread(see attached pdf and picture). According to them the CAN wires should go directly to T46s CAN separating connector in dash panel pin 6 High and 6 Low.

This is where I am at the moment. The park aasist module is not recognised.

Any suggestions to what may be wrong?

1. Wiring
2. Coding
3. Faulty control unit (J791)
 

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#2 ·
There's another thread on here Van and it suggested that maybe the can connections are too close between one another in the circuit.

jb:thumbsup:
 
#3 ·
I used a multimeter today and checked the continuity of the CAN wires and it is ok.

Furthemore, I checked the positive and ground connections and are working fine.

The voltage on the CAN wires is around 1.5 volts so there is some signal.

@JonnieB Thanks for replying Jonnie. I too have seen this post. If I get it right it implies that the resistance across the CAN wires is too low because the retrofitted set of wires is short compared to the various connections that normally happen within the main wiring harness.

I am not sure about this but I actually tested it today. I added another 3 meters of wire length making the total more than 6 meters. No luck...

I may try to measure the resistance across the CAN connection for J540 and try to replicate it for my retrofitted J791. Or even take J540 completely out of the system and use its CAN connection for J791. As explained in the first post the J791 CAN follows the exact same path as J540.

Another thought is that maybe VCDS is not capable of correctly registering the new module to the CAN gateway. Maybe I need to go to the Audi dealer to do it with VAS.

What about component protection? Shouldn't there be a component protection for the J791?
 
#4 ·
Hi Vanalex,

J791 does not have component protection.

The attached shows J791 attached to the Dash panel insert/suspension CAN bus, which confirms your earlier posts.

Still reading up on how the CAN gateway interacts with everything.....
 

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#5 ·
Thank you guys for the valuable info.

You may be right. I looked up some more info about how CAN lines should be:

Terminating Resistors:
Terminating resistors are used in CAN systems to create proper electrical
load between the CAN_H and CAN_L circuits. This load helps to reduce
electrical noise on the data circuits, which allows for a cleaner voltage signal
on the data bus.
Terminating resistors in the high speed CAN systems are required to be 120
ohms with a maximum range of 118-132 ohms. Lower speed CAN systems
may use different values. CAN systems can use split termination, which
means there may be more than two terminating resistors in the system.
Terminating resistors may be physically located inside any of the control
modules connected to the CAN harness, with a junction connector. The
resistors may also be part of the wiring harness.

Based on this I may try to add 120 ohms resistors to my cable. Most probably the relevant resistors are fitted within the audi OEM harness junctions. That is why my retrofitted line is not working.
 
#6 ·
Problem fixed. It was a CAN wiring problem. I replaced the CAN cables with new ones and the park assist module got recognised instantly.

I can get into the radio menu and change settings for the rear buzzer (the front one is not installed yet).

However, the park assist graphics are not working. Is it because the front sensors are not installed yet?

In VCDS I only get the error for the missing front sensors.

Is there anyway I can make it work before installing the front sensors?
 
#7 ·
Hi. Well done with fixing your problem and thanks for sharing your experience. As you may have read, I am also having can bus problems but mine are with a new rear camera controller.

I would like to replicate your success by doing it correctly so could you please give some more details:

Did you use standard 1mm2 16amp wire, or .63mm2 repair wire or some other can bus wire from your donor? If not from the donor, did you use the existing crimp connectors but replace the wire, or use repair wires and then lengthened them. After your analysis on resistance, were you careful about cable lengths or did you find it didn't matter.

Thanks in advance and sorry for all the questions but you've inspired me to get mine sorted :thumbsup:

PS Does anyone know where you can buy VAG crimps instead of using repair wires?
 
#8 ·
rs online (rs components) has all sorts of tools and even audi pin connector strips if you look hard enough:thumbsup:
 
#10 ·
Thanks - I just had a look at RS (haven't used them for years, since I was a PC dealer) but couldn't find anything VAG specific (plenty of other non-insulated connectors) so I'll give them a call. Thanks for the tip. :cheers:
 
#9 ·
Well as said it was all because of the cables.

I do not use audi repair wires at all.

I have bought on ebay the whole internal harness of an audi A5 for 100 euros. I have used this for quite a few retrofits.

What I usually do is remove the type of pins that is need for each plug and crimp it with cables from the donor to the needed length.

It does not really matter if the car I got the internal harness from was equipped or not with the component I want to retrofit. I find the proper plugs, remove the correct pins and use random cables to lengthen them.

The crimps I use are standard Red Heat Shrink Butt Connectors from ebay.

What probably went wrong with the CAN cables this time was me being lazy...

I used non CAN wire for part of the cabling because I was too lazy to remove the proper length of CAN wire from the donor harness...

As soon as I used ONLY CAN wire for crimping the right length everything was fine.

I did not use more the length needed.

The theory about wiring resistance was not correct. To tell you the truth it seems quite unlikely that couple of meters of cables would make a huge difference in resistance.

The 120 ohms terminator resistors already exist in the Audi CAN setting. One is located within each component and one is located within the central CAN connector (passenger dash where the CAN pins are fitted). So no need to add additional terminator resistors.

I can send you a few meters of CAN wires. I have lots.... But you will have to wait a bit because I will be abroad for work until the end of March. Let me know with PM.
 
#11 ·
I can send you a few meters of CAN wires. I have lots.... But you will have to wait a bit because I will be abroad for work until the end of March. Let me know with PM.
Vanalex - you're great! I'm picking up a repair wire from the dealer on Weds and will use one of the connectors to replace the broken one on the can bus twisted pair I have as part of the Kufatec kit. If that doesn't work I'll send you a PM either to take you up on your kind offer or otherwise find some suitable wire (which I think is .519mm2).