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RButcher
RButcher, BMW Technician
Category: BMW
Satisfied Customers: 103
Experience:  BMW Factory Master Mechanic, 609 A/C Certification
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94 bmw: traction control..power steering..you cant buy rebuild seals

Customer Question

Working on a 94 bmw 740 il. traction control unit was leaking on the power steering side so decided to replace it since it seems you can't buy rebuild seals for it. located used unit and installed. this unit did not appear to be working and also leaked. returned it a got a replacement used unit. this unit was installed. fully bled brake system. reinitialized asc+t unit. this unit also appears not to work. power steering/levelling side does not bleed off fluid. Note: first unit I installed did the same. almost acts like the pump on it is not working. rear end of car is dead and does not raise up when car is started. not sure if there is a relay on this unit or where it would be. the abs fuse is ok. Traction control light comes on and off when pushing switch on the dash. please advise.
Submitted: 5 years ago.
Category: BMW
Expert:  Cliff Burton replied 5 years ago.

Is your situation with the traction control? (Brake system) or the Hydraulic load leveling rear suspension? These are 2 completely seperate systems. Is this the unit you replaced in the trunk? - or are you working on the ASC unit under the hood?

Customer: replied 5 years ago.
the unit I replaced is the one under the hood, drivers side, bolted to the fender well. it has four lines from the abs connected to it on the brake side and three lines off the bottom on the power steering/levelling side. it has a bleeder on the top, as I mentioned, it does not appear to bleed as if no pressure is in the system.   the page you sent looks like something in the trunk, hydraulic pump for levelling? but not sure how that interacts with the unit I replaced.
Expert:  Cliff Burton replied 5 years ago.

What are the last 7 of your VIN number? The 1994 should have the rear load levelling system under the spare tire in the trunk.

The pics below are for the hydroboost power brake system- but are a completely seperate system from the rear level system according to the factory manual.

 

Customer: replied 5 years ago.
last 7 digits are RDE92442. My question still unanswered because I do not know how this information if true has anything to do or is affected by the unit I replaced. The manual makes no reference to it or procedures involving it when the traction control unit is replaced. I would need to know how to troubleshoot this system to find out why it is not working.
Expert:  Cliff Burton replied 5 years ago.

I guess I'm not understanding your question- your talking about two completely different systems here- The rear load leveling (rear height) and the traction control (ASC+T)

The above are ASC+T repair instructions. It sounds like your ASC system is working though- as the light is off until you press the switch to disable the system. If your concern is the back of the car not raising up- that is a completely seperate issue. Since I haven't been able to answer your question- I will opt out and let someone else give it a go.

Customer: replied 5 years ago.
THANKS, XXXXX XXXXX WAIT FOR ANOTHER ANSWER.    AS CLARIFICATION, I REPLACED THE ASC + T UNIT WHICH I THOUGHT TIED INTO THE REAR LEVELLING SYSTEM. AFTER REPLACING THE UNIT, IT DOES NOT BLEED AS IF THERE IS NO PRESSURE IN THE SYSTEM AND THE REAR DOES NOT RAISE UP. SOMEHOW THIS IS TIED INTO THE POWERSTEERING PUMP WHICH APPEARS TO BE WORKING OK.
Customer: replied 5 years ago.
MY QUESTION WAS TO BE TRANSFERRED TO ANOTHER EXPERT. I HAVE NOT RECEIVED A RESPONSE. PLEASE ADVISE.
Customer: replied 5 years ago.
Relist: No answer yet.
1994 bmw 740 il. replaced traction control unit because it was leaking with a used unit. first unit also leaked, got 2nd used unit. in both cases, followed procedure to fully bleed brakes and bleed hydraulic system. in both cases the hydraulic system (which is tied into the power steering and also levelling) does not bleed properly as if there is no pressure on it. The power steering seems to be working fine. when car is started, the rear does not raise up. all of this worked before I changed the unit. Need to know how this system is interconnected and find out where the problem is. please advise
Expert:  RButcher replied 5 years ago.
Do you still need assistance?
Customer: replied 5 years ago.
yes
Expert:  RButcher replied 5 years ago.
If I remember correctly the traction control computer does control the ride level system. The real question did you get the correct trac. control unit as not all 740's came with rear ride leveling. Also the traction control(abs) needs to be programmed and encoded to your specific vehicle as your car has more than the basic options. As for the powersteering the pump also provides pressure for the ride leveling if you don't have powersteering then more than likely the rear won't lift but not completely out of the question as it is a seperate pump section attached to the regular p/s pump. If this has been helpful please hit the ACCEPT button. If you have any more questions just ask.
Customer: replied 5 years ago.
I DO HAVE POWER STEERING. I DO NOT KNOW HOW THIS SYSTEM IS INTERCONNECTED TO THE LEVELLING SYSTEM TO XXXXX REAR WON'T RISE. THE PUMP APPEARS TO HAVE ONE PRESSURE LINE (GOING TO THE POWER STEERING BOX) AND TWO SUCTION LINES ON IT BUT I MAY BE WRONG. I HAVE DISCONNECTED THE ABS CONTROL UNIT AND RECONNECTED TO RESET PROGRAMMING BUT NOT SURE IF IS BEING RESET OR NOT. BRAKE SYSTEM ALSO BLED COMPLETELY. PLEASEA ADVISE.
Expert:  RButcher replied 5 years ago.
The traction control unit control the rear ride height, this is how the to systems are connected. If the traction control unit that you replaced is not correct for a ride height car, the car won't level out, it has the correct part or the correct program and coding, simple disconnecting the computer will not reset the programming it has to connected to a computer and the info down loaded to traction control unit. There is no bleeding involved other than starting the engine and making sure the powersteering fluid level is correct for the ride height. The programming and encoding will need to be done at a dealer or repair shop that has purchased the software and computer system to do this.
Customer: replied 5 years ago.
HOW WOULD I KNOW IF THE UNIT I PURCHASED IS SUITABLE FOR RIDE HEIGHT. IT IS A USED UNIT, LOOKS EXACTLY LIKE THE ONE I REMOVED. IT HAS FOUR BRAKE LINES FROM THE ABS AND THREE LINE FROM THE POWERSTEERING/LEVELLING SYSTEM CONNECTED TO IT. THATS WHY THE BRAKE SYSTEM HAD TO BE BLED ENTIRELY. BENTLEYS BOOK ONLY REFERS TO REINITIALIZING THE CONTROL MODULE AFTER REPLACEMENT, NOTHING ELSE. ADVSIE
Expert:  RButcher replied 5 years ago.
you will have to at check out the old part number on the original unit and compare to your. If not take the part number off of the unit that is on there now and check it at the dealer. If you replaced the metal hard component and the black computer you will need to get both part numbers.
Customer: replied 5 years ago.
used part number I purchased and part I removed are the same. computer control module not replaced, my problem is with a leaking hydraulic unit. I still do not know how the levelling system gets its pressure. There is one feed line on the pump that goes to the power steering box. I still don't understand how the contol module controls this. I reinitialized the abs/asc +t module per bentleys procedure. does this also have anything to do with operation of the levelling system operation, pump etc?   Please advise.
Expert:  RButcher replied 5 years ago.
The pressure for the self leveling system comes from the power steering pump, follow the lines from the rear shocks(leveler) forward you will find it so be a small diameter hose to feed the rear levelers. The levelers are computer controlled you should see a connector for each one after close inspection near the top if I remember correctly. The asc module just monitors ride height and operates the valves in the levelers, weather there is pressurized fluid there or not is another question.
Customer: replied 5 years ago.
Update: i have confirmed that I have a tandem pump and the pressure line goes the the asc hyd unit. there are three lines that connect to the bottom of this unit, all on the power steering steering side. Two have the same fitting and the third is smaller. Of the other two that have the same fitting, one goes to the reservoir and the other i think is the pressure from the pump. These could get mixed up and i don't think they are but i need to know which one goes where. i have no diagrams. right now, the line to the reservoir is closet to the fender wheel well. please advise if you know. I had to fix another leak on this system for the lines going to the cooler in the front of the engine, two short hose couplers, located under the brake booster. had to tear out the booster to get to them. fixed them, put the booster back in, filled the brake reservoir, started the car to back it off of ramps so i could bleed the brakes. car only ran for a minute but the pressure hose from the pump ruptured and it looks like the hydraulic unit leaked some fluid too a the same time possibly from overpressure. i don't know what happened. i realize the pump puts out 2000 psi but do not know what caused the hose to blow and unit to leak. note i did have the abs control module unplugged at the time. as you can see , this is turning into a nightmare of sorts. please advise if you can confirm which lines connect to the bottom of the hydraulic unit and where. i would think there should be some type of relief valve on this unit if it sees too much pressure so i don't know what's leaking on the unit. it was wet around the electrical cover on the side of the unit. i may have to pull it back out to see. this certainly wasn't designed to have it worked on. please advise.
Customer: replied 5 years ago.
ARE YOU ABLE TO ADVISE ON ABOVE REQUEST? I AM AHAVING OVER PRESSURE ISSUES WHEN I START THE CAR. AS NOTED ABOVE I RUPTURED THE PRESSURE HOS FROM THE PUMP. I REPLACED THE HASE AND BOTH END OF THE HOSE CONNECTIONS ARE LEAKING AND THE TRACTION CONTROL UNIT IS LEAKING FROM ONLY RUNNING THE ENGINE FOR 30 SECONDS. I NEED TO CONFIRM THE LINE CONNECTIONS TO THE BOTTOM OF THE ASC + T UNIT TO MAKE SURE I DO NOT HAVE THESE LINES SWITCHED. AND IF THEY ARE OK, I DON'T KNOW WHAT THE PROBLEM IS. PLEASE ADVOSE

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