ABS Warning Light ALWAYS On

[Alan]

Hi All.

I wonder if anybody can please advise on my best course of action to rectify an ABS issue I face on my M535i (M30B34).

I've read lots here about ABS troubleshooting, and I'd like to get to the stage where actual troubleshooting occurs, but my initial issue is unusual, that being, the ABS warning light stays on. As in, always on, when the ignition is switched on, and when the car is running. The warning lamp goes off when the ignition is switched off.

The ABS light/system, does not do a check where, like on other posts I've read, the lamp briefly turns off, and then back on, to highlight that there is a fault. Mine just stays on.

Any of you good folks able to point me in the right direction? I have the Bentley manual too, just to mention.

The actual brakes feel firm, but do stop the car when enough pressure is applied. All new discs and pads. I don't hear any prining of pumps either when the ignition is turned on.
Fuses are fine in the fuse box beside battery.

TIA

[vinceg101]

Off the top of my head:
1. One of the ABS wheel sensors has gone bad (wire nick, etc.)
2. The Electronic control unit has gone bad (bad solder joints, etc.)
3. The relay on the ABS unit has gone bad
4. One of the wires to either the ABS unit is damaged

The latter two are relatively easy to troubleshoot and fix.
The first two are a bit more involved since you need a known good sensor to test. Since these are NLA from BMW, you have to source a good used ones (borrowing one from someone is likely the best route). If the wheel sensor is bad, Ivo Christov sells new ones. Ebay for the control unit is best.

You should test the ABS to see if it indeed not working, it could be a bad cluster or light.
And yes Bentley has a whole section in the Brake chapter to testing the ABS system.

[Blue Shadow]

When the light comes on helps diagnose the problem. If a wheel sensor is bad the light will come on with engine start and go off until the car starts moving forward and the problem sensor does not provide a signal...prior to that the computer thinks things are ok.

I would expect that the light on all the time means the abs system knows there is a fault in the computer or relay at the pump and the light just does not go out.

If the light doesn't come on (after start up sequence) until you hit higher mph (kph) then there is a bad tone ring sending an intermittent signal to the computer that is more correct at lower speeds. This is usually a rusty tone ring on a rear wheel hub.

[Chimi-Changa]

Tone rings in the rear can easily be checked if you jack up the rear end there is a open space that when you spin the wheels you can see the entire ring from underneath. If there are any that are chipped or corroded that could be causing the fritz. I think Ivo sells the tone rings separately too.

[Alan]

No idea as of yet, but thank you for the helpful advice.

I'll start with relay swapping and connections to the ABS unit.
The car is in a Carcoon now, and I'm tight on time, but there's always the Christmas holidays for working on the car!

Logically, yes I agree, the system isn't even going into diagnostic mode, so the problem may very well be obvious.

Out of curiosity, is there an overhaul/repair kit I can buy for the ABS unit? I looked and didn't see anything too obvious for sale.

[stuartinmn]

Tone rings in the rear can easily be checked if you jack up the rear end there is a open space that when you spin the wheels you can see the entire ring from underneath. If there are any that are chipped or corroded that could be causing the fritz. I think Ivo sells the tone rings separately too.

If the tone rings are clogged with dirt or rust, cleaning them with a small wire brush may help.

[Alan]

Can anyone please advise, from experience, if these two allen key screws are bleed points for my ABS pump? (E28 M535I, 1986) I am not seeing any brake fluid from them. I consistently have the abs warning light, that quickly flashes twice when starting car, but stay on after that.Four wheel speed sensors have around 1k ohms, and 0.3-0.5V when rotating the wheels by hand. Also, to mention, the abs pump makes three quick clicks from the relay (one of the two), when I turn on ignition. Function test on abs pump, from control module plug in dash, activated the abs pump motor, and also clicking from each of the four solenoids in the abs pump unit. Any and all advice is HUGELY appreciated. Head is melted trying to solve this. 
ABS unit has been pulled apart. All is now clean and clear inside the unit.I just want the ABS system to function correctly. TIA

[gadget73]

Just eyeballing it, I'd figure those might be fluid passages from the lower to the upper plate, and the screws cap them off.  Probably not really intended as a bleed port, just a plug. 

No experience, just what it looks like to me. 

[Alan]

Hi Guys. 

I'm STILL trying to troubleshoot this absolute headache.

I just want my abs system to work!!!

E28 M535i,  1986. M30b34

Turn on ignition, abs light on, 3 or 4 quick clicks from abs pump.

The 3 grounds at the abs ecu are good. So are the three (i think) 12v switched power. No 12v when ignition is off.

X4 wheel speed sensors read around 1k ohms when hand spinning through wheels.

A function test of the abs pump, jumping wires at the abs ecu plug, activated the abs pump motor, and all four solenoids clicked.

Chat GPT is sending me down the garden path, and if I keep going , I will end up in Wonderland!!! Helpful, but going in circles now.

Abs light stays on, even with abs ecu disconnected, and ignition in the on position. 

Cracked all hydraulic connections at the abs pump, and fluid at each.

Brakes seem fine when driving.

Separately, maybe, the power windows relay under the dash is constantly clicked on, even with key removed. Interestingly though the battery holds voltage over weeks with no restart issue. That may have changed now with all my messing. Cutting the thin red wire from pin 30 to 86 de-energises that solenoids.

Now, am i to start buying oarts? Relays, ecu?

Check control system not working. Rear Windows not working.

C302 accessory connector has a bridge/short between Abs pin and the one directly under it. (Can't recall offhand what the pin ID is, but it's directly under) C302 appears healthy and I cleaned it.

Ive read evertthing i can. Used chat gpt, read the Electrical manyal for the 528 and 535i maybe 300 times!! 

Please share any advice if you have any. 
 

[///M]

What part of Dublin are you in? You can send me a private message