9.2.2. General information about diagnostics of malfunctions

Refusals of automatic transmissions can be caused by five main reasons: inefficient operation of the engine, violation of adjustments, problems with hydraulics, mechanical malfunctions or failures of the microprocessor or alarm network. Diagnostics of these malfunctions always has to begin with check of the reasons which are most just subject to correction: level and condition of transmission liquid (Head Routine maintenance of the car), adjustment of drafts of the selector and drive of a butterfly valve. Then it is necessary to make road check for the purpose of definition of changes in work of AT after the made corrections and need of further researches. If the problem is not fixed, further diagnostics has to be made by dealer office of service of the BMW company or a specialized workshop of car service. Apply for information on possible malfunctions of AT to the Section Diagnostics of Malfunctions of Automatic Transmission at the end of this Chapter.

Preliminary checks


  1. Make a short trip on the car to warm up AT up to the normal working temperature.
  2. Check the level of transmission liquid as Routine maintenance of the car is described in the Head:
    • If liquid level too low, make having added to the level designated by tags on the measuring probe then make external examination of transmission on identification of signs of leaks.
    • If the level of liquid is unusually high, merge surplus, then check the merged liquid for existence of a cooler in it. Presence at transmission liquid of a cooler of the engine speaks about violation of tightness of the internal walls of a radiator separating a cooler from transmission liquid (see the Head the Cooling system).
    • If liquid is made foam, empty transmission and fill it with fresh liquid, then check whether is not present in the merged cooler liquid.
    • Check a condition of liquid on the measuring probe. Normal color of transmission liquid - dark red. If it brown, or has a "burnt" smell, merge it and fill transmission with fresh liquid. If liquid in bad condition, can indicate it or lack of regular leaving, or internal violations in work of transmission.
  3. Check idling turns.

If it is obvious that the engine is faulty, you do not perform preliminary checks work of transmission before malfunction correction.

  1. Check freedom of the course of a cable of the drive of a butterfly valve in the mode kik-Down. If necessary adjust it (see the Section Adjustment of the Drive of the Lever of the Selector).

The cable of the drive of a butterfly valve can normally function at the switched-off and cold engine, but create problems after its warming up. Therefore you make checks of a cable both at cold, and at the heated-up engine.

  1. Check a condition of draft of control of the selector (see the Section Check of Work and Replacement of the Switch of Resolution of the Start/switch of Fires of a Backing). Make sure that it is correctly adjusted and works smoothly.

Diagnostics of leak of liquid

In most cases it is easy to find leak of liquid by external survey. Repair usually consists in replacement of an epiploon or laying. If leak at external survey does not manage to be revealed, the actions offered below can help.


  1. Define a liquid grade. Make sure that transmission liquid flows away, but not motive oil and not brake fluid (transmission liquid has dark red color).
  2. Try to reveal a leak source. Make a short trip on the car, then park it over a big leaf of a pure cardboard or the newspaper. In a couple of minutes you will be able to reveal leak, having defined the place on a cardboard where liquid drips.
  3. Make careful external survey of the site of transmission suspected of leak and area around it. Pay special attention to joints of the interfaced surfaces of laying. For survey of remote sites it is useful to use a pocket mirror.
  4. If the source of leak does not manage to be found, carefully wash out the suspected site solvent, then dry it.
  5. During the movement of the car the air stream can blow off the following liquid or oil on other components, complicating definition of a source of leak. After cleaning of the suspected site or make a trip on the car at a small speed (to minimize an air stream), or let's it get warm up to the working temperature, without moving a little (in this case completely cock the parking brake). Banish the engine at different speeds and several times carry out the transmission selector through all provisions. After that examine the suspected component again.
  6. After identification of a source of leak for its competent elimination it is necessary to define the leak reason. If to replace laying, having left curved a landing flange, leak will not stop. The curved flange needs to be aligned.
  7. Before trying to eliminate leak, make sure of performance of the listed below conditions, otherwise it can repeat.

Some of the listed below conditions cannot be executed without use extremely of specialized tools and due qualification of performers. It is necessary to leave such problems to specialists of dealer office of BMW or specialists in transmissions from a workshop of car service.

Leaks through laying

Regularly check a condition of the pallet of a case of transmission. Check existence of all bolts and reliability of their tightening, a condition of the pallet (dents in the pallet can lead to damage of the case of the valve inside).

If laying of the pallet proceeds, then too high level of liquid, obstruction of a sapun, pulling of bolts of the pallet, a pallet flange bend, damage of a sealing surface of a case of transmission or damage of the laying can be the reasons. If for consolidation between the pallet and a case of transmission sealant is used, then it is possible that sealant not of that grade is applied. Leak can happen even because of existence of cracks or porosity in casting of a case.

Leaks through an epiploon

Too high level or pressure of liquid, obstruction of a ventilating sapun, damage of walls of a nest of an epiploon, damage or the wrong installation of the epiploon, damage of a surface of the site of a shaft passing through an epiploon or the weakening of fastening of the bearing causing excessive degree of freedom of a shaft can be the reasons of leaks through an epiploon.

Make sure that the nut of a tube of the measuring probe is strong tightened. Regularly check for existence of leaks the site around a gear wheel of a speedometer or the sensor of speed. At detection of transmission liquid check whether the sealing ring of round section is damaged.

Leakages of a case

If leaks in the case are found, it indicates existence of porosity in its casting which should be eliminated, or to replace a case.

Check reliability of fastening and a condition of nipple connections of hoses of a cooler.

Liquid follows through ventilating or jellied tubes

It is a sign of overflow of transmission, hit in it of a cooler, the wrong installation of the measuring probe, obstruction of a ventilating sapun or openings of discharge.