Specifications

Testing Testing Transmission Systems

Table 4-9 provides two sample interpretations of BMW automatic transmission identification

codes, located on the transmission side plate.

4.2.2 Transmission Systems

BMW uses automatic transmissions made by two different suppliers: GM and ZF.

• GM—Hydramatic is a manufacturing division of GM located in Strasbourg, France producing

smaller transmissions used for lower output engines such as the M42 and M50.

• ZF—German company, “Zahnradfabrik Friedrichshafen” commonly known as ZF

transmissions. ZF manufactures both manual and automatic transmissions.

There are approximately 24 different control system versions. The transmission and control

system technology becomes more sophisticated through the model years. The advancement is

mainly due to the integration of total vehicle system communications sharing information on a

common communication bus (see “Testing Bus Systems” on page 44). This allows the

transmission control module to read information from other controllers on the same vehicle, which

it uses for smoother and more efficient shift control regardless of the operating conditions.

BMW transmission control systems are listed as EGS or AGS.

• EGS is German for “Electronic Getriebestuerung” or “Electronic Gearbox.”

• AGS is German for “Adaptiv Getriebestuerung” or “Adaptive Gearbox Control.”

Both EGS and AGS have different driver-selectable shift programs. However, AGS can

automatically adapt and select the appropriate shift program depending on driving style or

operating conditions. AGS has everything that EGS has plus the following:

• Shift points adapted to driving style

• No upshifting when driving in a curve

• Auto determination and selection of winter program to improve traction (2nd gear start-up)

• Stop and go traffic auto recognition, eliminating 1st gear for improved comfort

Both EGS and AGS have adaptive hydraulic pressure control. Transmission slip ratio (input speed

to output speed) and slip time (amount of slippage during a shift) are monitored by the TCM. By

comparing target and actual slip, the TCM can adapt by modifying the pulse width modulation of

the main pressure solenoid. This increases clutch apply pressures compensating for internal slip

resulting from clutch wear and optimizes shift performance.

Table 4-9 Sample BMW automatic transmission ID codes and explanations

A5S 310Z 4HP24 (EH)

A = Automatic, or S for Standard

5 = Number of gears

Overdrive Ratio: S = Top Gear Overdrive;

D = Top Gear Direct Drive

310 = Maximum Input Torque Rating in Nm

Z = Manufacturer: R = Hydramatic; Z = ZF

4 = Number of Gears

HP = Hydraulic Planetary

24 = Maximum Torque Rating in Nm (22-220)

EH = Electro-Hydraulic Valve Body;

H = Hydraulic Valve Body