As I’ve mentioned, the ABS and DSC lights had been blazing in my 1999 Z3 ever since I bought the car about a year and a half ago. I’d inspected the ABS sensors at all four wheels for torn wires, and tested their resistance: All checked out, yet the lights remained on. Web forums were full of posts from people whose cars had similar symptoms, many reporting that the culprit was the ABS control module.
A common trail of breadcrumbs involved using a scan tool and finding an 071 code for failure of the ABS pump. The prevalent idea seemed to be that it’s much less likely that the pump itself is bad, and much more likely that the control module isn’t turning the pump on. So, on one of these interminably cold snowy Boston winter weekends, I borrowed a fancy Autologic scan tool from my employer, Bentley Publishers.
Sure enough, when I scanned the ABS, it rang up 071.
Okay, then, I thought, here’s the trailhead. Wonder how long it’ll take me to hike to the witch’s house?
The first step was to remove the ABS control module from the pump. In my car, this was utterly trivial; there is a large electrical connector that you pull off first; then there are four small E5 Torx-head bolts you need to remove. The smallest Torx in my socket set was an E6, but I found that a standard 4-mm socket fit the E5 heads almost perfectly. I had read that on other cars, it’s challenging to pull the wiring harness out of the way of the module to get it out, but in my Z3, there was unimpeded access. I probably had the module out in 90 seconds.
Then, of course, came the question: How do you fix it? There were numerous references online to places to which can could send the module and get it fixed for a few hundred bucks. It is reported that the car is completely drivable with the module removed, though the idea of driving it through weather with the ABS control rods exposed gave me the heebie-jeebies. It was a moot point in my case anyway, as the Z3 is unlikely to see duty during this snowy winter unless some disaster with my E46 wagon requires it to be pressed into service.
As I read online, I learned that different BMWs have different ABS control modules—which may have different failure modes. Folks with E39s, for example, report finding broken fine gold wires inside their modules, whose repair is hampered because the printed-circuit board (PCB) and the wires inside the module are encased in a kind of goo. However, it appeared that my Z3 had a module manufactured by ATE—one also used on Volvos—whose reported problems were nearly always due to cracked solder joints. The problems could reportedly be solved by simply opening up the module, finding the cracked joints, and re-flowing the solder.
Right, then; let’s do this thing.
I got out my soldering iron and a big magnifier and prepared to inspect every solder joint on the PCB. I looked at the module. It had a plastic case and cover that were joined at a seam—and I could not figure out for the life of me how to open it up. When I tried gently prying the cover off with a small screwdriver jammed into the seam, the brittle plastic of the cover instantly began to crack. I backed off.
More web-searching, mostly on the Volvo side of the fence, revealed the answer: The case isn’t really designed to be re-opened. You have to cut the plastic. There were reports of doing it cleanly with a utility knife inserted along the seam; one fellow reported taking literally hours to do it neatly this way. But there were also references to taking a Dremel tool and just, um, doing what needed to be done.
I found a video of someone doing exactly that. It was ugly. It was nasty. It was quick. It was exactly my speed.
Figuring that I had little to lose, I dug out the Dremel and the cutting wheel and cut the cover about halfway up the small shouldered slope it made with the base. In about ten minutes, I had cut it all the way around. I was a bit mystified that the cut piece didn’t immediately fall off, but it turns out that there are three holes on the underside that sit on plastic dowels that protrude upward through the PCB. A gentle pry, and off it came.
Next came the actual repair. One Volvo forum did a particularly good job of photographing the visual evidence of cracked solder joints. Look primarily at where the big posts come through the PCB, it said. This is where the wiring-harness connector comes into the board, and where the power connector leaves the board to power the ABS pump itself. Sure enough, the two solder joints on the posts leading to the ABS pump were cracked. Even on the big posts, though, the solder joints are relatively small, and cracks are not easily visible to the naked eye—but when viewed through a high-quality magnifier, they were pretty obvious, looking almost like petals of a flower, where they should instead look more like a small rounded dome. I heated them up with my soldering iron, re-flowed the solder, and put another dab of solder on each for good measure.
One of my Hack Mechanic pointers is to verify a repair as early as possible—that is, check out whether whatever you did actually works and solved the problem before you button everything up. I put the module in the car with the PCB completely exposed, connected the wiring harness to it, and started the car.
The ABS and DSC lights stayed on. Damn!
Then I remembered reading that the module has to see a few rotations of the wheels to verify the functionality of the ABS sensors before it clears a fault. It wasn’t snowing out at that moment, but the roads still had all sorts of slush and salt on them. I pulled the module back out, snapped the cover on—meaning that I pressed the dowels back into their holes—put a baggie around the module, held the baggie in place with a rubber band, and temporarily installed the module in the car, turning in two of the Torx-head bolts.
I pulled the car out of the garage—by itself a bit of a feat, as the driveway slopes downward toward the garage and was a sheet of ice; in fact, I thought that if the ABS and DSC didn’t come on, I might have a difficult time safely negotiating my way in and out. When I got to the top of the driveway, the lights were still on: double damn! Well, I have the baggie around the module, I thought. I’ll give it a hundred feet on the nasty street.
I began driving down the street, and in about half a block, both the ABS and the DSC lights went out. Joy beyond all measure!
I pulled the car back in, pulled the module back out, and buttoned it up. I’d read that, ideally, RTV or silicon should be used to seal the hack job done with the Dremel, but the gaps I’d made seemed to yawn open much too wide for silicon or RTV to sit complacently in without dripping all over the PCB. Hot glue seemed to be the thing. I used it in copious quantities.
I popped the glued-up module back in the car, tightened everything down, drove it another hundred feet, verified that I hadn’t broken it, and then put the car away. Yes, the irony that I’d most need the ABS and DSC during the exact weather I’m hoping to avoid is not lost on me; I’m waiting for March to do its out-like-a-lamb thing so I can drop the top.
In my 40-ish years of wrenching, there are repairs I’ve thoroughly enjoyed, and there are certainly ones I’ve utterly loathed—replacing the seal between the master cylinder and the power-assist booster in the E28, outside, during the winter, comes to mind. While my unequivocal recommendation to anyone else is not to attempt to fix an ABS control module, and instead to pay the $200 to have someone else fix it, for me this was a wonderful, satisfying repair.
But more than that, until this happened, I’m not sure that I’d ever come face-to-face with a repair where, had I taken the car into a dealer because the lights were on, I might have been charged nearly two grand—that’s what I’m seeing online for dealer quotes to replace the ABS pump—and instead, I fixed the problem myself for literally nothing.
And this did fix it; it’s not like I simply bypassed the warning lights. Some days, I love being the Hack Mechanic.—Rob Siegel
Got a question for Rob Siegel, the Hack Mechanic? You can find him in the BMW CCA Forums here!
Rob's book Memoirs of a Hack Mechanic is available through Bentley Publishers, Amazon, and Bavarian Autosport—or you can get a personally inscribed copy through Rob's website: www.robsiegel.com.
