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post #1 of 7 (permalink) Old 04-12-2019, 05:32 PM Thread Starter
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BCM Fixed :-)

I finally found the fault in my BCM and I fixed it.
Everything electrical work in our car now and I am really happy about it

To make a long story 'short-circuited...':

We have had two main issues with our Kappa, one was the Passenger prescense sensor for the airbag system and the other was that the courtesy light and the driver side unlock circuit did not work.

After many hours of trying to fix a broken lead in the PPS we decided to send the SDM unit to Berlin to delete the PPS and passenger seatbelt routines so now the Passenger Airbag is always active regardless of occupancy of the passenger seat. (Very important to never put any backward positioned children seat there!!!)

After hours and hours of troubleshooting and forum searching I finally concluded that the other issue was the BCM. I asked for a quote for a new BCM with reprogramming here in Sweden. (Please sit down) : Quote: $1000... This fact really inspired me to further investigate the issue with the BCM myself. I could state the the origin of the fault was the relays on the BCM. These relays control the Inadvertent load for the courtesy light and the door lock/unlock circuits. I tried to use a neodym magnet to externally trig the relays and, voila, the mirror lights turned on. The previous owner had made an idiot fix of the other issue with the door locks. He obviously connected the passenger door lock actuator with a wire directly to the driverrs side door actuator. This is really crazy since the logic in this circuit swithes the polarity to lock/unlock the doors which means that this solution short circuits the logic directly to the ground. This is why they had put a 25A relay in the BCM... Total lack of knowledge about electrical engineering...

After the summarizing of the faults I decided to try to change all the automotive relays on the BCM. I ordered new Matsu****a high quality relays ones from an Ebay-shop in Bulgaria which arrived in a week.
Before the operation I drawed a connection diagram to be sure where every relay had its connection on the PCB.
I then desoldered and removed the old relays from the BCM. (Took about two hours with a soldering braid under a Microscope connected to a monitor).

When all the old relays were removed I carefully went through all couplings on the pcb to see if anyone was damaged. I actually found one lead that was broken under a relay so I replaced this with a cable.

I then soldered the new Bulgarian relays to the PCB and checked the connections and everything seemed fine.

Reinstalled the BCM in the car and wow. The courtesy light worked . YEE.

However the driver side unlock circuit did NOT work...

Again took out the BCM to the workbench and tried to decode whatever GM's engineers once did in their offices...

I could see that all the coils on the relays where connected to 12V and the control computer actually grounds the relays in order to actuate the functions. Now I could see that there was some logical grounding circuits on one side of the coils soldering points on each relay. The PCB's seem to be of a multilayered type so you cant actually trace the leads by "eye". I Must have measured a thousand points on the PCB when I finally found a point where I reconed it should be contact but there was none. :-O

One of the "passthroughs" from one side of the PCB to the other had no connection with one of the coils. (Guess which one) YES. The driver side unlock circuit.

I then soldered a "piggy back cable" from the ground side of the relay coil to the circuit where I supposed there should be continuity.

Back in the car again the test was a real thriller. Both me and my wife looked, smelled and listened if there should be any crazy things happening when I connected the battery to the car.......

The clicking sound of the CD changer made us shiver, but... then... Silence.

Maria testet to lock and unlock the car with the remote and YES !!! Everything worked. We fixed it !!!

(Attaching some pictures to make you see how small these soldering points are)

If we had left the car at a workshop to fix all these things the cost here in Sweden would have ended in just about $2500, now the bill ended in $200 (and a lot of work). However we learned a lot on the way so I consider this rather interesting. :-)

We ended this friday sitting in the Opel (Sky Redline) in the garage listening to music and drinking a beer before the sauna. It was a real moment. :-)
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Last edited by Kjelle69; 04-13-2019 at 03:10 AM.
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post #2 of 7 (permalink) Old 04-12-2019, 05:51 PM
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Congratulations! Very inventive fix. But you forgot a picture of the beer.
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post #3 of 7 (permalink) Old 04-12-2019, 07:12 PM Thread Starter
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Ah. :-)

Best regards from us in the very North of Sweden @JohnWR


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Congratulations! Very inventive fix. But you forgot a picture of the beer.
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post #4 of 7 (permalink) Old 04-12-2019, 08:57 PM
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That is some cold beer!
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post #5 of 7 (permalink) Old 04-13-2019, 02:26 AM
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Great to see that you fixed with careful diagnostics and troubleshooting instead of taking the typical workshop route of throwing expensive parts at it...rare to see these days.

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post #6 of 7 (permalink) Old 04-24-2019, 04:44 PM
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Hai @Kjelle69,

Congratulations that this repair was also successful. Compliments for the way in which you have done this. You've earned a beer
Hopefully you can now drive smoothly for a while.

Still no annoying error messages regarding the passenger airbag?

Greetings

Walter
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post #7 of 7 (permalink) Old 04-25-2019, 04:55 AM Thread Starter
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No more warning lights and all the electronics works just as it did when it was new :-)
Next plan is to get a tune, looking on Trifecta's power pak or possibly to dig deeper in the HPTuners tech.
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