ABS Control Unit Repair DIY

[Slowpokee]

Today I fixed my ABS control unit after replacing every wheel sensor first. I know there are places that repair them for several hundred dollars. However, I decided to attempt the repair my self. I wouldn't recommend this unless you have a good stereoscopic microscope and a steady hand. A few years back I started repairing watches for a hobby so I have some experience soldering under the scope and working with delicate parts. So if you have the tools, patience of a saint and 1/2 a day to do the repair you can do the repair.

The point of failure on these devices is the microscopic wire used to terminate the board to the box. It's covered in Silicon and will break over time due to expansion and contraction of the Silicon substrate. This along with matching the ECU to this device has ensured BMW income on a part that should by all means never fail. Especially when related to safety. This seems common with Volvo as well. Anyway rant over. below are the instructions.

Tools needed: Stereoscopic microscope, Dremel with grinding wheel, soldering iron, thin gauge solder, stranded wire (22 gauge), Xacto knife, tweezers, qtips, break cleaner, clear Silicon and hot glue gun.

Time: 6-8 hours

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1) Remove top cover of ABS unit to expose internal circuit board and connections. I started on the three outer edges where I could see the inside of the enclosure with a flash light. The final 4th side by the connector is cut straight down. Try to cut as close to the connector as possible. The terminals inside are a few millimeters out so be extra careful when cutting this part.
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2) Remove the silicone between the outer terminal and the circuit board. There will be plastic chunks stuck to the silicon from the removal process. Don't try to remove it as any pressure or poking could damage the microchip connections which are also using microscopic wires to terminate. This could be another point of failure if your not careful. I used the Xacto knife to scrape the silicone away and tweezers to pluck it out. Use a qtip dipped in break cleaner to remove the rest of the silicon on the board. Remove all the wires between the board and terminal now.
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3) The fun part. Using the soldering iron, tint the terminals and pads on the board. Note the pads are extremely thin and could melt if you keep the iron to long or too hot. I plucked a single strand of wire out of a 22 gauge wire about an inch. Start at the terminal and solder the wire. Cut to length to the board pad and terminate the pad.
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4) Cover the terminals, new wires and any exposed components with the clear silicon. Wait a few hours for it to dry and cure. Use a hot glue gun to secure the panel back to the control unit.
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Finally, re-install, say a quick prayer and turn the key. My yellow triangle ABS light went off immediately. Others have had to drive above a certain speed to reset/clear the error. My guess is it depends on which microscopic wire detached would determine the failure and how it resets it self.

Best Regards,
Mark O.

[Slowpokee]

Here is a photo of the original wires. When I removed then I felt tension on all but one which is probably the culprit. To my surprise it was one of the thicker wires. Perhaps the thinner wires allows for more play?
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Here is a photo of the microchip on the board. Normally these components are soldered to the board as on every smart phone, embedded device and micro-controller.
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