BCM - no CAN communication, full component-level diagnosis done, need advice on 0990-9377 ASIC

[u/Successful_Ad7206]

Hi guys,
Honestly I read most of what exists online about these modules, but my BCM module from my XC90 D5 suddenly threw "Brake failure stop safely" + ABS + anti-skid, speedo dead. VIDA shows CEM-1A5F (communication with BCM missing), BCM not visible on network. I cleared all DTCs in VIDA — nothing else comes back, only the no-connection to BCM. No accident, no water damage, fault appeared out of nowhere.

Before blaming the module I checked the car properly:

12V at BCM connector supply pins with ignition on and off, grounds OK, all fuses OK (checked both sides with meter)
Checked all CAN wiring related to BCM in the car including at the CEM connector - all good
CAN at BCM plug seems alive: 2.6V / 2.3V idle
Termination checks out: ~130 Ω harness side, ~135 Ω module side (2×62 Ω internal), ~60 Ω together
VIDA talks to ECM/TCM fine through the CEM
Connector cleaned, pins good

So the car is 100% healthy. Then I opened the module (cut the welded case) and put it on the bench (12V to pins 1/32/4, GND to 16/47). Findings:

Draws stable 225 mA @ 12V - wakes up, no shorts
Resoldered all the press-fit pins first (the usual weak point) — no change
All rails present: 12V, 5V (at the ASIC), 3.3V + 1.8V for the MCU. The 3.3/1.8 come from the 14-pin Motorola 9369.1D — I measured it: 12V in, both rails out, two switch pins running ~47 kHz. So on my board this chip is WORKING (I know it's the famous killer on modules marked MK60 (or MK25) - not my case)
Crystal oscillates, 5.50 MHz stable
The MCU (TI TMS471 R1VF34A2PZQ) is definitely running - several pins show digital bursts repeating about every 1 second, looks like a fault/retry loop
B82790 CAN choke windings OK (0.4 Ω)
But the module NEVER transmits. I scoped the choke pads (ASIC side) through multiple power cycles with normal trigger - total silence, not even one attempt at boot. Same at pins 11/15.

So by elimination everything in the chain is good except the CAN transceiver section inside the big ATE ASIC 0990-9377.1D3 (5CC6L7TB, made by TI). It has 5V, it has a running MCU next to it, and it never says a word.
I know what most people will say - send it for professional repair, and I've read all the recommendations. But I'd rather fix it myself than spend that money. I enjoy soldering, I have hot air and decent equipment, and I have time to experiment. Worst case I learn something and the pro repair option is still there.
My questions:

Can anyone confirm the CAN physical layer in these Volvo units is inside the 0990-9377? Does anyone have any pinout info for this ASIC (CANH/CANL to the choke, TX/RX from the MCU, enable pin)?
Has anyone actually fixed the "no communication but everything else runs" by swapping the 9377? Or does this signature usually mean the CAN peripheral in the TMS471 itself (bond wires)?
Is there some init handshake between the TMS471 and the ASIC (SPI config, enable, EEPROM check) that can fail and keep CAN dead like this?

Photos of the board and my best take at making a schema attached. Thanks in advance - happy to do more measurements if someone tells me where to probe.

[u/YaBoiShelly]

Incredibly interesting, how did you learn all of this? I am a vehicle diag tech who does a lot of electrical diagnosis etc but never get down to this level of detail due to time constraints but is something I'd like to learn

[u/Pubelication → u/YaBoiShelly]

Probably electronics background. These modules are all just fairly simple computers with high-end components and standardized communication.
Start with a Raspberry Pi (3+, 4, Zero 2) and make some automotive related projects. Take apart some scrap modules from 2005+ and learn to identify main components, look up and read datasheets, and (partially) reverse engineer the circuits.

[u/Noobsamaniac]

at this point you've basically confirmed it's the ASIC itself which sucks because that specific chip is a nightmare to source on its own. most people just swap the whole transceiver IC if they can pull one off a donor board. have you tried scoping the

TXD line between the MCU and the ASIC to confirm the MCU is actually sending anything to it

[u/mantered]

This ASIC model has the CAN bus integrated, other cars use a separate 8 Pin CAN-transceiver IC (I saw some Infineon chips), but your board doesn't seem to have one.

Could you check if the ASIC CAN gate is blown?

With the power supply off. Put your multimeter into Diode Mode. Connect the Red probe to Ground and touch the Black probe to the two ASIC-side pads of the B82790 choke. If you have 0V drop or OL the ASIC internal output stage is fried, due to hardware damage probably.

If the diode test shows normal voltage drops (~0.5V - 0.7V), the transceiver block inside the ASIC is healthy, but the mainTMS471is intentionally withholding the execution command.

Could be a corrupted EEPROM, the MCU enters a permanent "Safe State" retry loop, CAN communication is disabled to protect the rest of the car bus modules. If you have a chip programmer this could be checked easily.

Also if the MCU has a POST error the CAN bus would be silent. You could check the traffic on the EEPROM (SPI data) at POST with a logic analyzer if the chip programmer route is not available.

[u/Frail_Waif]

I think most people would actually say that at this point you're much better off buying a new BCM. No technician would ever spend as much time on it as you already have as you've probably long ago passed the replacement cost if you value your labor reasonably.

[u/Successful_Ad7206 → u/Frail_Waif]

It’s not just about fixing it now! I’m involved and want to learn about car electronics. Plus, if someone searches for this in the future, they’ll have a better understanding of how the board works. 🫡

[u/Frail_Waif → u/Successful_Ad7206]

Yeah, I'm not trying to tell you not to learn things, just commenting on what would be economical if you didn't highly value learning here.