Ok, I absolutely agree that the ABS wiring is not particularly straightforward. But I've got an interesting story for you from my previous E39 from several years back. I took my 528i to the dealer because my ABS light went on. They charged me about $210 to replace the right rear abs sensor. The minute I got in the car I noticed that I had no speedo and the ABS light was still on. The dealer said that it was a coincidence because the speedo is controlled by a sensor in the transmission. The dealer service guy also recommended, even though he said the problem was a sensor on the transmission, that I replace all three of the other ABS sensors for another $600 for the ABS sensors and $400 for the transmission sensor. Reason? BMW recommends it because all ABS sensors tend to fail together. Hmmm.... $1000 to replace a few sensors? Homework time! I own the BMW TIS and ETK CDs and the two volume E39 Bentley manual. Both show the speedo connected to the left rear ABS sensor in the schematics. I bought a single ABS sensor for the left rear wheel. I jack-standed the car, pulled the wheel and replaced the sensor in an embarrasingly (for the dealer that charges $210 for this) brief 10 minutes. Speedo problem fixed. ABS problem gone. Now, just in case there was something going on with the transmission sensor, I bought two of these transmission speed sensors and was prepared to install them. A drawing I found on the Pelican site showed where they should be. I searched all over the transmission for these sensors and could not find them. Both of my E39s at the time had A5S 360R transmissions. Not sure if they are internal, on top of the transmission well, or just not there for my version but I sure couldn't find the sensors! Fortunately, that car never developed an ABS problem again and I sold it a few years later to buy a convertible. Happy ending to chapter one.
Chapter 2 is a little longer...
About 6 years ago I came across another nearly perfect E39 wagon for my wife, who had finally decided to dump her minivan. I practically stole the thing and it ran flawlessly with little more than oil changes for nearly 6 years. The car now has a hair over 200k miles on it. Well...back in August my wife was driving it when it threw both belts. Just as she got it someplace where she could park it, something ruptured dumping all the coolant. My non-BMW mechanic said the engine was toast and tried to tell me the head gasket was blown. I did not believe him. Why? No peanut butter anywhere. (If you've seen a blown head, you know what I mean.) I had it towed to my house. The engine started and ran fine but whether running or not, any coolant added would just run out of the engine someplace and end up on the ground. I figured if I was going to junk the car, I might as well take it apart to see if I can find the problem. After letting it sit for about a month, I finally got a chance to wrk on it and figured out that the heater bypass pipe that runs along the engine under the intake manifold had ruptured where it enters the block behind the thermostat housing. I ordered a few parts to see if that was really it, pulled everything off the engine on the intake side so I could get to the pipe (air box, MDK/throttle, fuel rail, injectors, all hoses and connectors and the intake manifold). I replaced the pipe and pressure tested the cooling system to make sure that was the problem. No leak! I took the opportunity while reassembling to change all the breather, secondary air, and vacuum lines and controls, many of which which were brittle or split. I also changed the spark plugs, coolant hoses, pulleys, fan cowling, a couple of leaky sensors and the power steering reservior (with six flushes of dirt-grey PS fluid first). Of coure I changed the oil and flushed the coolant myself just to make sure I didn't see any evidence of a blown head gasket. None present. Inside the car I also changed the steering yoke so the wheel buttons worked and the SRS light would go out (an issue from before the overheating) and replaced the ignition switch to resolve the phantom electrical issues with the radio, steering wheel adjustment, dash and interior lights, etc. (also from before the overheating...terrific Youtube video on this issue). The car now runs quiet, clean and at exactly the right tempurature with no OBD or SRS errors and no gremlins. Well...the only OBD error is the secondary electric fan, which is because the previous owner replaced it with a unit that apparently doesn't handshake properly. It works fine, kicks in at the correct temperature and does not turn on the check engine light. I've been driving the car nearly daily for about a month now including a couple of long trips and the mechanicals seem just fine...except for the ABS.
Chapter 3 is in present tense.
Unfortunately, this E39 has a single DSC light on (the circle). No "ABS" light, no "Brake" light. The cruise control is not working and there are no codes. I've just started troubleshooting it. I started by jacking the car, pulling the ABS connector and testing the signal from each wheel. I discovered no signal from the left front ABS sensor...which seems odd as I would have expected an ABS light, too. I swapped the wheel sensor for a new one. Still no signal, so I suspect the hub. The car has 200k on it and I've never replaced any of the hubs, so I'm going to do that next starting with the front...part troubleshooting and part sanity check as the left front hub makes just enough noise to not be right. When I get ABS sensor signal from all four wheels, I'll start troubleshooting whatever else is going on. I'm not going to go nuts on a car that has this kind of miles on it, but I would like to keep it as a winter car for at least another year and as long as I spend less than a car payment per month working on it, I'm coming out ahead and am learning some things in the process.
Ok, you've read this far. Thank you.
Any ideas on the ABS? I'm pretty sure Im just getting started.