jhwhite
Active Member
The following has many details, maybe too many details, but I hope it is better than too few details. I have searched all over and people do not seem to know how to fix this problem.
High-level description: Aforementioned car will not start ("hybrid error"). Dealer did diag and proposed to change the entire HV battery and BCM battery control module, a costly repair that is in excess of car value. I declined and towed the car home.
Low-level description: ODIS output file from dealer indicates that the CANbus communication with the BCM is not operating, and that this is the reason for the no-start. I confirmed this with oscilloscope as follows: There are CAN signals going into the BCM on the T8ax/1+2 connector pins, but there is indeed no data coming back out, as checked by disconnecting the T8ax and scoping the CANbus on the BCM/battery side (I'm using schematics of the vwts(dot)ru site).
How the car got into this state is unknown. My best guess is that a low-voltage on the 12V battery caused some errant signal (maybe airbag) and that the ECU and/or J234 (Airbag control module) somehow disabled both the BCM itself *and* the BCM CANbus. Maybe a crash-shutdown of BCM, although there was never a crash. Something like a P1609 but additionally disabling the BCM CANbus, so that the P1609 cannot be observed nor cleared. So I am stuck.
Debugging details: I have the BCM (J840, 5C6915182B) extracted from the car, and I'm testing it on my kitchen table, rigging up the scope to the CANbus using a pinout I found on youtube for an Audi that very likely has the same pinout for at least the relevant Vdd/GND/CANbus pins.
Now, CANbus has no signal, but I can see some mV-level burst-like noise that *might* be the ghost of a CANbus signal leaking through a High-Z driver. Other checks I did: I punctured+scratched the protective lacquer (a.k.a the "conformal coating") on BCM pcb502 (full name at bottom) and was able to verify that the 12V-to-5V switching converter is working and providing 5V. Idd(12V)=10.8mA, which seems low, not sure. Was not able to locate/probe the internal CANbus traces yet. R(CANbus+/-)=7.85kohm, which is perhaps not surprising since the 120ohm terminations are elsewhere and not inside the BCM.
Additional speculation: The Dealer ODIS output also says that the car has the fault "18187 - Service Mode Active", and it says this mode was active when the car was brought in. I wonder if service mode is in some sense turning off the BCM CANbus so that a technician cannot accidentally turn on the HV battery (as a safety measure), same as, or in addition to, a "crash shutdown". But I have no idea how I can reset or clear this mode or any other mode inside the BCM, given that the CANbus is not functioning. I don't think it is the CANbus itself that is broken. I'm thinking there is some bit or bits that need to get flipped, but how?
Related to J234 Airbag Control Module possibly generating a crash-shutdown: The BMC has the following inputs via the T14x connector outside the battery as follows.
T14ax/1 : p500 says connected to J234.T100/74=Airbag control module. NBNB: could be related to battery locked
T14ax/2 : p500 says connected to J234.T100/75=Airbag control module. NBNB: could be related to battery locked
I don't know whether setting these signals to the correct voltage would wake up the CANbus. And I do not know the pattern needed (00,01,10,11). Neither do I know on the BMC numerous connectors these signals would be located. Not able to find a schematic from Sanyo or VW. Could posssibly trace/ohm from T14ax to BMC connectors A-F (100s of pins) and find out.
The big question: If I can get the CANbus to wake up (and I need some help with that), would connecting a VCDS *directly* to the BCM let me clear whatever error codes are disabling the BCM (assuming my overall theory is correct)?
Conclusion: Could really need some help here. How does my analysis sound? Does anyone know some of the details that I am missing?
Part numbers or names:
Battery 5C6915590C (a.k.a AX1)
BCM 5C6915182B (a.k.a J840)
BCM PCB1 model number: Sanyo 2RR4B14A69501 == 2rr4b14a69501
BCM PCB2 model number: Sanyo 2RR4B14A69502 == 2rr4b14a69502
J234 Airbag control module
High-level description: Aforementioned car will not start ("hybrid error"). Dealer did diag and proposed to change the entire HV battery and BCM battery control module, a costly repair that is in excess of car value. I declined and towed the car home.
Low-level description: ODIS output file from dealer indicates that the CANbus communication with the BCM is not operating, and that this is the reason for the no-start. I confirmed this with oscilloscope as follows: There are CAN signals going into the BCM on the T8ax/1+2 connector pins, but there is indeed no data coming back out, as checked by disconnecting the T8ax and scoping the CANbus on the BCM/battery side (I'm using schematics of the vwts(dot)ru site).
How the car got into this state is unknown. My best guess is that a low-voltage on the 12V battery caused some errant signal (maybe airbag) and that the ECU and/or J234 (Airbag control module) somehow disabled both the BCM itself *and* the BCM CANbus. Maybe a crash-shutdown of BCM, although there was never a crash. Something like a P1609 but additionally disabling the BCM CANbus, so that the P1609 cannot be observed nor cleared. So I am stuck.
Debugging details: I have the BCM (J840, 5C6915182B) extracted from the car, and I'm testing it on my kitchen table, rigging up the scope to the CANbus using a pinout I found on youtube for an Audi that very likely has the same pinout for at least the relevant Vdd/GND/CANbus pins.
Now, CANbus has no signal, but I can see some mV-level burst-like noise that *might* be the ghost of a CANbus signal leaking through a High-Z driver. Other checks I did: I punctured+scratched the protective lacquer (a.k.a the "conformal coating") on BCM pcb502 (full name at bottom) and was able to verify that the 12V-to-5V switching converter is working and providing 5V. Idd(12V)=10.8mA, which seems low, not sure. Was not able to locate/probe the internal CANbus traces yet. R(CANbus+/-)=7.85kohm, which is perhaps not surprising since the 120ohm terminations are elsewhere and not inside the BCM.
Additional speculation: The Dealer ODIS output also says that the car has the fault "18187 - Service Mode Active", and it says this mode was active when the car was brought in. I wonder if service mode is in some sense turning off the BCM CANbus so that a technician cannot accidentally turn on the HV battery (as a safety measure), same as, or in addition to, a "crash shutdown". But I have no idea how I can reset or clear this mode or any other mode inside the BCM, given that the CANbus is not functioning. I don't think it is the CANbus itself that is broken. I'm thinking there is some bit or bits that need to get flipped, but how?
Related to J234 Airbag Control Module possibly generating a crash-shutdown: The BMC has the following inputs via the T14x connector outside the battery as follows.
T14ax/1 : p500 says connected to J234.T100/74=Airbag control module. NBNB: could be related to battery locked
T14ax/2 : p500 says connected to J234.T100/75=Airbag control module. NBNB: could be related to battery locked
I don't know whether setting these signals to the correct voltage would wake up the CANbus. And I do not know the pattern needed (00,01,10,11). Neither do I know on the BMC numerous connectors these signals would be located. Not able to find a schematic from Sanyo or VW. Could posssibly trace/ohm from T14ax to BMC connectors A-F (100s of pins) and find out.
The big question: If I can get the CANbus to wake up (and I need some help with that), would connecting a VCDS *directly* to the BCM let me clear whatever error codes are disabling the BCM (assuming my overall theory is correct)?
Conclusion: Could really need some help here. How does my analysis sound? Does anyone know some of the details that I am missing?
Part numbers or names:
Battery 5C6915590C (a.k.a AX1)
BCM 5C6915182B (a.k.a J840)
BCM PCB1 model number: Sanyo 2RR4B14A69501 == 2rr4b14a69501
BCM PCB2 model number: Sanyo 2RR4B14A69502 == 2rr4b14a69502
J234 Airbag control module
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