Hello.
Posting this as a giving-back to the forum which has helped me out many times over the years.
Since last November I have struggled with intermittent brake, dead gauges, and transmission system errors. They come in flurries of great frustration several months apart and have defied my means to properly diagnose. From other posts in this and other forums I came to believe that the root problem was the CANbus errors reported, but my ability to repair was confused by seemingly random self-repairs as the problems went away again. Just as soon as I started digging to the CEM or BCU the problem would vanish again and even though I did try repairs I was never sure that what I did was the fix and that the issue hadn't just gone away.
My more successful and immediate fixes, which at the time I thought were the permanent fixes, were:
- Replacing the battery and re-making every chassis connection I could find, believing a dirty connection to ground was introducing random voltage drops and even introducing electrical noise as the car vibrated the bad connection.
- Extracting the CEM and attaching a heatsink to the NXP/Freescale CPU.
- Re-mating every computer connection I could find. The Big CEM and BCU connectors, the DIM connector, and re-fitting the TCU and ECU units in the engine box (a royal PITA without the handy-dandy tool!). Replacing the fan there for good measure.
Last week my CANbus symptoms returned and I suffered intermittent and then permanent errors which eventually prohibited engine start and a wholesale CANbus failure message (U0073). That cloud had a silver lining because for the first time I was able to experimentally diagnose the issue without the problem hiding again. Most damning was that after learning that it was OK to start and run the car even with the BCU detached I was able to absolutely prove to myself that the problem was at the BCU or the connector to the BCU. When it is connected the car was dead as a dodo, just crank, crank, crank and no fire and the U0073 bus failure message. When disconnected I could 'see' the other modules using the stalk-foglight on/off method and the engine ran, the gauges moved, the transmission shifted, and the bus error was gone.
After thoroughly wiggling all the BCU connector pins and making sure they were good I also verified (with the battery disconnected) that the rest of the car presented 120 Ohms between the CANbus pair (white, green wires to pins 11 and 15 of the BCU connector) and ~13kOhms between ether CANBus wire and chassis ground and 12V Battery. The jig was up! The fault was 100% at the BCU. I was in a nothing to lose situation as my BCU was dead as it was.
First I tried opening the BCU using a craft knife to cut out the flexible mastic/sealant in the bead around the BCU lid. After narrowly avoiding a serious knife injury in the process I decided to inflict more serious pain on the BCU. I used a Dremel router bit to cut out a window in the lid above the BCU connector. I wasn't being tidy - I just set to with the Dremel and the guard to limit how deep the router bit cuts. I was not in a mind to be neat but if I were to do it again I'd probably cut a tidier more rectangular hole by setting up some guides rather than just hand-guiding it.
I carefully applied a joint of solder to each of the pins, paying close attention to the CANbus on pins 11 and 15, but making a clean bright joint on each. You will need a brutal iron ~ 40W for the power pins and even some of the signal pins as the connector pins are large and have a good thermal mass and sink to the connector body, and they join to large 'lands' in the circuit board which act as heatsinks. Be careful, use a magnifying glass, etc etc and you can do it. If you want to be conservative then inspection of the wiring loom behind the BCU connector will show you the comparatively few pins which actually carry a signal so you could limit your attentions to just those pins, I suppose. In the following picture the green wire top left is pin 15, the white wire below it pin 11. Generally, every such green/white pair (twisted together in the loom throughout the car) will be a CANbus.
I then re-sealed the BCU using some plastic cards (I used old hotel room card-keys, but whatever material you have will work provided you have the adhesive needed to bond it to the remaining lid). And, because every repair needs duct tape I used some over the whole patch to provide a further seal.
I am a little puzzled about why a bad joint, which I would have presumed to be an open-circuit and therefore not to have affected the car CANbus would have been fixed by my making good joints. But, my car-wide bad CANbus was fixed by this method and I have now made dozens of small cautious journeys and some long ones in an Arizona summer. No faults reported.
I do have a lingering 'Transmission Service Required' message but I know that is only because the TCU saved some CANbus error reports. I can have that cleared when I visit my friendly local transmission guy and spot him a beer to use his tools to reset the code I cannot reach myself with my simple OBDII tool.
Anyway, if nothing else I hope this gives someone the courage to Dremel open their BCU to effect a repair and the information to know what is behind the lid of a 8671224 BCU.
