BCM Powertrain to OBD II (Switched) queries

[digitalsucks]

Hi all

I have a pq25 bcm (two t73 connectors) and the powertrain can bus is allegedly "switched" through the obd connector (t16) i'd like to know more about how i could force this connection to be always on as it appears theres a relay in the j519 bcm module itself for this.

Here's the wiring diagram for the BCM, it shows two pins 22, 23 which are exposed to the OBD II port

Please see my autoscan below

Chassis Type: NH-SK25 (6N0)
Scan: 01 02 03 04 08 09 10 15 17 19 25 2E 37 44 56


01-Engine -- Status: OK 0000
02-Auto Trans -- Status: OK 0000
03-ABS Brakes -- Status: Malfunction 0010
04-Steering Angle -- Status: OK 0000
08-Auto HVAC -- Status: Malfunction 0010
09-Cent. Elect. -- Status: OK 0000
10-Park/Steer Assist -- Status: OK 0000
15-Airbags -- Status: OK 0000
17-Instruments -- Status: OK 0000
19-CAN Gateway -- Status: OK 0000
25-Immobilizer -- Status: OK 0000
2E-Media Player 3 -- Status: OK 0000
37-Navigation -- Status: OK 0000
44-Steering Assist -- Status: OK 0000
56-Radio -- Status: OK 0000
-------------------------------------------------------------------------------
Address 01: Engine (J623-CAYB)       Labels:. 03L-906-023-CAY.clb
   Part No SW: 03L 906 023 QK    HW: 03L 906 023 LK
   Component: 1,6l R4 CR td H33 6952 
   Revision: --H33---    Serial number:               
   Coding: 00254016002500080000
   Shop #: WSC 73430 031 00008
   ASAM Dataset: EV_ECM16TDI02103L906023QK 003003
   ROD: EV_ECM16TDI02103L906023LL.rod
   VCID: 7F5B087CF77DD1430A8-802A

No fault code found.
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans        Labels: 0AM-927-769.clb
   Part No SW: 0AM 300 062 N    HW: 0AM 927 769 D
   Component: GSG DSG AG7     431 6203 
   Revision: 00043014    Serial number: X
   Coding: 0000020
   Shop #: WSC 73430 790 00008
   VCID: 372B205C934D2903828-8062

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes (J104)       Labels: 1S0-614-517.clb
   Part No SW: 1S0 614 517 L    HW: 1S0 614 517 L
   Component: EBC 460 ESP   H16 0023 
   Serial number: X
   Coding: 94CC487889B200F6290012F991AE00804F0C00
   Shop #: WSC 73430 031 00008
   ASAM Dataset: EV_Brake1ESPEBC460TRW 002004
   ROD: EV_Brake1ESPEBC460TRW_002_SK25.rod
   VCID: 3829236092D3267B8B2-806C


-------------------------------------------------------------------------------
Address 08: Auto HVAC (J255)       Labels: 6Q0-907-044.lbl
   Part No SW: 5JA 907 044     HW: 5JA 907 044
   Component: Climatronic   H05 0106 
   Revision: A1001000    Serial number:  X
   VCID: 78A9E360D2D3E67B4B2-802C


-------------------------------------------------------------------------------
Address 09: Cent. Elect. (J519)       Labels:. 6R0-937-08x-09.clb
   Part No SW: 6R0 937 087 R    HW: 6R0 937 087
   Component: BCM PQ25 H+4  H34 0424 
   Revision: BF034001    Serial number: X
   Coding: 3D980BA000E9140092080E307E4B0CC81E80400F608E0040020000004000
   Shop #: WSC 73430 790 00008
   VCID: 4CC16FB0F6CBBADBDFA-8018

   Subsystem 1 - Part No: 5J0 951 172
   Component: DWA-Sensor H0  H03 1211
   Coding: 000000

   Subsystem 2 - Part No: 1K0 951 605 C
   Component: LIN BACKUP HO  H05 1501
   Coding: 000000

   Subsystem 3 - Part No: 5J0 951 172
   Component: DWA-Sensor H0  H03 1211
   Coding: 000000

   Subsystem 4 - Part No SW: 5E0 919 719 F    HW: 5E0 919 719 F
   Component: E221__MFL-PR6  H05 0130
   Serial number: X
   Coding: 820000

No fault code found.

-------------------------------------------------------------------------------
Address 10: Park/Steer Assist (J446)       Labels:| 5JA-919-475.clb
   Part No SW: 5JA 919 475 A    HW: 5J0 919 475 A
   Component: PARKHILFE 3K  H11 0005 
   Revision: --------    Serial number: X
   Coding: 100103
   Shop #: WSC 73430 031 00008
   ASAM Dataset: EV_EPHVA14SK25X0000 001002
   ROD: EV_EPHVA14SK25X0000.rod
   VCID: 44D14790DE1B729B17A-8010

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags (J234)       Labels:| 5Q0-959-655.clb
   Part No SW: 34D 959 655 B    HW: 34D 959 655 B
   Component: AirbagVW20    005 0366 
   Serial number: X
   Coding: 88CCC00000000000540000C8008000000065
   Shop #: WSC 73430 790 00008
   ASAM Dataset: EV_AirbaVW20SMEVW253 001110
   ROD: EV_AirbaVW20SMEVW253.rod
   VCID: 343117508EBBC21BA7A-8060

   Crash sensor for side airbag: driver side:
   Subsystem 1 - Part No SW: -----------    HW: 480 411 704 15
   Component: SideSensor_Df  003 0148
   Serial number: X
   Coding: 2D2D2D

   Front Passenger's Side Airbag Crash Sensor:
   Subsystem 2 - Part No SW: -----------    HW: 480 411 704 15
   Component: SideSensor_Pf  003 0148
   Serial number: X
   Coding: 2D2D2D

   Rear Side Airbag Crash Sensor (on driver's side):
   Subsystem 3 - Part No SW: -----------    HW: 480 411 704 15
   Component: SideSensor_Dr  003 0148
   Serial number: X
   Coding: 2D2D2D

   Passenger side rear thorax airbag crash sensor:
   Subsystem 4 - Part No SW: -----------    HW: 480 411 704 15
   Component: SideSensor_Pr  003 0148
   Serial number: X
   Coding: 2D2D2D

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments (J285)       Labels:| 5K0-920-xxx-17.clb-SRI1
   Part No SW: 5JA 920 940 E    HW: 5JA 920 940 E
   Component: KOMBI         H06 0709 
   Serial number: 00000000000000
   Coding: 411A01
   Shop #: WSC 73430 031 00008
   ASAM Dataset: EV_Kombi_UDS_VDD_RM09 A04723
   ROD: EV_Kombi_UDS_VDD_RM09_004_SK25.rod
   VCID: 3D273274BDF10353584-8068

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway (J533)       Labels:. 6N0-909-901-6R.clb
   Part No SW: 6N0 909 901     HW: 6R0 937 087
   Component: GW-K-CAN TP20 H34 0424 
   Revision: BF034001   
   Coding: 932300
   Shop #: WSC 73430 790 00008
   VCID: 70B9DB40BAA3BE3B832-8024

No fault code found.

-------------------------------------------------------------------------------
Address 25: Immobilizer (J334)       Labels:| 5K0-920-xxx-25.clb
   Part No SW: 5K0 953 234     HW: 5K0 953 234
   Component: IMMO          H06 0709 
   Serial number: 00000000000000
   Coding: 000000
   Shop #: WSC 00000 000 00000
   ASAM Dataset: EV_Immo_UDS_VDD_RM09 A03710
   ROD: EV_Immo_UDS_VDD_RM09_VW23.rod
   VCID: 6A8DC9289CFF44EBCD6-803E

No fault code found.

-------------------------------------------------------------------------------
Address 2E: Media Player 3 (J650)       Labels:. 5N0-035-342.lbl
   Part No SW: 5N0 035 342 G    HW: 5N0 035 342 G
   Component: SG EXT.PLAYER H19 0770 
   Revision: A1001003    Serial number: X   
   Coding: 030100
   Shop #: WSC 73430 790 00008
   VCID: 2B030C2C53059DE3F60-807E

No fault code found.

-------------------------------------------------------------------------------
Address 37: Navigation (J794)       Labels:| 1K0-035-27x-37.clb
   Part No SW: 5JA 035 192 Q    HW: 5JA 035 192 Q
   Component: RNS315-EU   H85 0501 
   Serial number: X
   Coding: 040004010207000001000002
   Shop #: WSC 73430 031 00008
   ASAM Dataset: EV_RNS315EUV2UDS 001705
   ROD: EV_RNS315EUV2UDS.rod
   VCID: 45D75A94D5214B93004-8010

   Data carrier:
   Subsystem 1 - Part No: 3AA 919 866
   Component: EUR_W_V7  0066

No fault code found.

-------------------------------------------------------------------------------
Address 44: Steering Assist (J792)       Labels:| 6Rx-909-144-V2.clb
   Part No SW: 6R2 909 144 R    HW: 6R2 909 144 E
   Component: EPS_TRW_ALow  322 3111 
   Serial number: X
   Coding: 0055
   Shop #: WSC 73430 790 00008
   ASAM Dataset: EV_SteerAssisUDSTRW 011021
   ROD: EV_SteerAssisUDSTRW_011.rod
   VCID: 47CB509CEF2D5983F28-8012

No fault code found.

End----------(Elapsed Time: 01:29, VBatt start/end: 12.0V/12.0V)-----------

 

[dnoermann]

It is not a simple relais inside the BCM.

The BCM acts as a can-bus gateway.
In PQ25 in the BCM there is 09 Central Electrics and 19 Gan-Bus-Gateway, and 61 Batterie regiulator, all in one Physical Control unit.

So inside there is a Microcontroller with a lot can-interfaces.

1x Diagnose Can
1x Engine Can
1x Comfort Can
1x Cluster Can

And this Microcontroller is routing/bridging the can Frames beetween those different CAN Busses.

Ah sorry now i understand, you are referring to those "Switched" Engine Can bus pins.
Whell there is realy a relay inside.
In later Versions this Relais is externaly.
This is for the Can Bus of devices which are being easy accessable from the outside.
This bus is disabled so that the canbus can not be accessed while car is parked ...
I know no way in software to always enable this relais, but you can open the device and just find it and electricly bridge the contatcs of the relais ...

 

[digitalsucks]

Hey dnoermann, thanks for the insight - the external relay should be reflected in the wiring diagrams correct? I presume as the pinout reflects it as switched direct from the BCM it's going to be inside the module.

Will have a peak and try and trace some cables back.

 

[Robert Z]

Perhaps you are reffering to relay J788 which is controlled by ignition switch, see below.

https://imgur.com/a/6jHBaax

 

[digitalsucks]

Sorry for the delay getting back - hope you all had a good christmas

Perhaps you are reffering to relay J788 which is controlled by ignition switch, see below.

https://imgur.com/a/6jHBaax

My car doesn't actually have J788 according to the wiring diagrams, I have a device which will communicate on CAN through the OBD II connector but the switching never occures.

Looking at the wiring diagrams I can only assume this is fully controlled in the BCM/Can Gateway.

 

[DV52]

@digitalsucks: Hi. Hmmmmmmmmm..........I've been reading this thread with interest (really odd arrangement - switching the powertrain CAN bus), but I'm confused!!

I've taken the relevant section of the CAN schematic from @Robert-VW post above and added the part of T6 WD that relates specifically to the J788 - J519 interface (the circuit where the BCM controls the CAN switching relay) like this:

So - for versions of the T6 where the CAN switching relay is a physical device that lives outside the BCM - why isn't the solution as simple as joining together the wires on T9 /9 to T9 /8 and T9 /5 to T9 /3 on the J788 connector? Or, even simpler - just remove the T73a /8 BCM wire on the J788 connector and earth T9 /2 (assuming that the BCM doesn't monitor the health of the coil on the CAN relay)?

And - for versions of the T6 where the CAN switching relay is embedded inside the BCM, why isn't the solution as easy as joining the +ve powertrain CAN input wire to the +ve powertrain CAN output wire on the BCM connector and doing the same with the -ve powertrain CAN wires on the BCM connector (I don't have a WD for this version of the T6 - but see the schematic in lower part of picture)?

What am I missing - why is this anymore complex?

Don

 

[digitalsucks]

So in my case, I was hoping to find a way to switch the relay without making physical modifications to the wiring loom itself The solutions you've listed for both scenarios would absolutely work as it bypasses the relay itself completely, I'd like to know under what circumstances this actually switches.

I've put my wiring diagram below for reference of this layout.

 

[dnoermann]

I'd like to know under what circumstances this actually switches.

This is for the Can Bus of devices which are being easy accessable from the outside.
This bus is disabled so that the canbus can not be accessed while car is parked ...

I think with Ignition OFF this Bus is switched off.

 

[DV52]

I think with Ignition OFF this Bus is switched off.

@dnoermann: Yes, I suspect that you are correct - but I think that it's more complex than just an ignition switch-off condition. I'm guessing really, but if the design logic for switching the powertrain CAN bus via J788 was only to disconnect it during ignition OFF - this could be done more simply by connecting the switching relay to a T15 fuse and earthing the other end of the coil.

Since I don't have the complete wiring diagram for the T6 (I thieved the circuit for my picture above from the T6 forum), I'm not sure if SC14 in my post above is T15, or T30. In any event, because the other end of the coil in J788 is connected to the BCM (pin # t73a/ 8) I suspect that some other logic is at play. The wiring arrangement for the coil in J788 looks like a classic "logic-AND" circuit to me - but again, I'm guessing!

So yes, I agree that likely ignition OFF/ON is a requirement to energize the coil - but an additional condition is provided by the BCM for switching (perhaps, key insertion or proper operation of the Terminal 15 voltage supply relay??).



Don

 

[iichel]

The J788 is in fact a physical relay in PQ25 cars, it opens when the ignition is switched off. it will prevent the powertrain canbus being accessible from the ACC radar connector or SWA connector.

 

[Robert Z]

Agree 100%.
I wasn't precise enough in my previous post.
This relay has its coil supplied with permanent +12V via fuse on one side and on the other side the BCM provides GND when ignition is switched ON.

https://imgur.com/a/2LA02kh

 

[DV52]

The J788 is in fact a physical relay in PQ25 cars, it opens when the ignition is switched off. it will prevent the powertrain canbus being accessible from the ACC radar connector or SWA connector.

@iichel: I've no problem with your assertion - I agree . That's not my point. My question is; is this THE ONLY condition for j788 switching?

If SC14 in my picture is a T15 supply on PQ25 cars, then the wire to the BCM is redundant if ignition OFF/ON is the ONLY condition. If on the other hand SC14 is a T30 supply - then the wire to the BCM must provide a more compelling logic (like making sure correct-key insertion, or proper operation of J327- maybe)

I guess the real question is WHY; Why switch the powertrain CAN bus (yes, "it will prevent the powertrain canbus being accessible from the ACC radar connector or SWA connector." - but why do this?)

Don

EDIT: Arrrhh......thanks @Robert-VW. So SC14 is a T30 supply - this suggests (to me) "more compelling" logic is provided by the BCM!

 

[Robert Z]

My interpretation is that it is anti-hack solution for all CAN wiring outside of the vehicle.

 

[DV52]

My interpretation is that it is anti-hack solution for all CAN wiring outside of the vehicle.

Robert: OK, thanks - then the "compelling logic" must be that earthing wire from the coil of J788 to the BCM ensures that the ignition is correctly switched-on by the proper key insertion process - which if done with the correct key, subsequently causes the BCM to energise the car's T15 rail via J327!! QED

Don

 

[iichel]

Do, tt73n/8 is a switched ground controlled by the bcm. But I think you already figured it out