E32 ABS sensor testing procedure

[Annddrriy]

There is no ABS overvoltage relay the main relay supply power to ABS module pin 1. ABS overvoltage relay is need it because when wheels braking in slipery road wheel is not unlocking but it is locking up brake booster on foot brake pedal. ABS hydraulic unit It should unlock wheel which is on slippery road but at this point it unlock brake booster master cylinder on foot brake pedal. In slippery road hydraulic unit unlock brake main master cylinder instead to unlock brake cylinder near wheel. How it is unlocking main master cylinder when road is slippery ? Hydraulic unit releasing fluid pressure on brake lines which is connected to the foot main master cylinder but it should release fluid pressure on brake lines which is connected to the wheels brake cylinder. That is big difference between hydraulic foot brake master cylinder and wheel hydraulic brake cylinder.

[whiskychaser]

How to check what type of relay is in place between K5 and K7 relays ?

Page 0660-00 of the diagrams confirms which relay is used in the location and it depends on the car in question. Diagrams also show that the sockets for the two relays K10 and K51 have the same number of pins. But the wiring diagrams show that X54 for K10 is black and X941 for K51 is white.

[Annddrriy]

Doesn't matter what it shows the matter what is there and how it works. That is big difference between hydraulic foot brake master cylinder and wheel hydraulic brake cylinder. ABS hydraulic unit releasing fluid pressure on brake lines which is connected to the foot hydraulic master cylinder but it should release fluid pressure on brake lines which is connected to the wheels hydraulic brake cylinder.

[Annddrriy]

1988 year shows on diagram page 0660-00 K10 ABS relay and on page 6105-02 shows K51 phone alert relay. Is that means relays K51 and K10 two relay in one place shares for ABS module and phone alert ?

[shogun]

there is 1 empty space for a relay http://www.e32-schrauber.de/bmw/date...db-4_09_89.pdf and that says either K10 on 750 or K51 on 735, different relay in same place based on engine
for 750 * K10 X54 ABS overvoltage protection relay
for 735 * K51 X941 phone alert relay

look at the top 7 drawings, there you can see all relay boxes by built year, and K10 is always for something different and even the location changed http://www.e32-schrauber.de/bmw/s-relaisbelegung.htm

[Annddrriy]

Yes you are right that is for 750iL only. Have a look on diagram page 0660-00 1991 and same page 1988 no relay but in wiring diagram there is relay. That 1988 is old school always works and new school always run. Main relay supply power to the ABS module and transmission TCU and ignition coil. Ignition coil needs proper current to fire spark plugs if current draw ABS module and transmission TCU there won't be enough current for ignition coil that is why engine misfire at idle. If to wire it ABS module feed current wire to phone alert relay it will work ? Thanks in advance for your answer !

[Annddrriy]

The engine misfire not of current draw from main relay of ABS module. The engine misfire at idle of CID sensor not working right ?

[Annddrriy]

Guys what would you advice to do with ABS hydraulic unit not working right. When car moving on icy road all wheels keep locking up ABS pump works on hydraulic master cylinder only instead unlocking all wheels on slipery road. Could be mess in hydraulic brake lines connection. Wrong hydraulic brake lines output ? If locking up front wheels the hydraulic pressure not releasing from front wheels in hydraulic cylinder the pressure releasing from foot hydraulic master cylinder that releasing pressure should be releasing on front wheels not on hydraulic master cylinder. Thanks !

[shogun]

Might be a defective hydraulic unit or ABS control unit, but that is just speculation. I personally would send the hydraulic unit and the control unit to a pro shop which tests, reman , repairs these units.
But that is not cheap. Or first try another used ABS control module

[Annddrriy]

Master cylinder two input lines releasing pressure from hydraulic unit when any wheels catch icy road.
If those two hydraulic brake lines of master cylinder would be connected to the output of the hydraulic unit of the front wheels and front wheels hydraulic brake lines would be connected to the input of the lines master cylinder then hydraulic unit would activate front wheels hydraulic brake cylinders on both side left and right. ABS hydraulic unit activate master cylinder lines instead to activate lines of front wheels hydraulic brake cylinders left and right side.
Rear left wheel should not lock up rear left wheel when wheel catch icy road when pessing foot brakes.
For an example rear left solenoid of hydraulic unit should be activated of ABS speed sensor.
ABS hydraulic unit.png