IDENTIFICATION
Identification plate is located on side of transmission case. (Scheme 12) Identification plate information may be required when ordering replacement components.
Scheme 12
DESCRIPTION & OPERATION
Note. Electronic control diagnosis and code retrieval procedures are not available for BMW.
Automatic transmission is electronically controlled, providing 4 forward speeds and one reverse speed. Transmission consists of a torque converter, clutches, planetary gears and brake band. (Scheme 13)
Transmission shifting and torque converter lock-up are controlled by the control module. The control module receives information from various input devices and uses this information to control shift solenoids, band apply solenoid and Torque Converter Clutch (TCC) solenoid. The control module uses input signals to control the force motor solenoid operation, which activates the pressure regulator valve for controlling the line pressure.
A torque management control system is used to reduce engagement shock caused by a change in vehicle speed during shifting. For additional information on the electronic control system, see AUTOMATIC TRANSMISSIONS DIAGNOSIS article.
The control module contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if a specified failure or problem is present in the transmission electronic control system. If fault has set a DTC, the CHECK TRANS light on instrument panel will flash. The DTC may be retrieved to determine transmission problem area. For additional information on self-diagnostic system, see AUTOMATIC TRANSMISSIONS DIAGNOSIS article.
Transmission is capable of 3 different shift modes, Normal (NOR) mode, Power (PWR) mode and Winter mode. Shift mode may be selected by POWER or WINTER mode switch mounted on center console, near gearshift lever. Shift modes are used to change transmission shift points for various vehicle operating conditions. For additional information on shift modes, see AUTOMATIC TRANSMISSIONS DIAGNOSIS article.
The control module contains a fail-safe system. When a failure or problem is present in the transmission electronic control system, the control module may go into a back-up mode using pre-programmed values, allowing vehicle to be driven. The CHECK TRANS light on instrument panel will flash to inform driver of a problem. Vehicle can be driven, but shifting must be done manually. When manually shifting transmission, if shift lever is placed in "D" or "3" position, transmission remains in 4th gear. If shift lever is placed in "2" position, transmission remain in 3rd gear. If shift lever is placed in "L" position, transmission remains in 1st gear. If shift lever is placed in "R" position, transmission will shift into reverse.
Transmission is equipped with shift and key lock systems. Shift lock system prevents gearshift lever from being moved from "P" position unless brake pedal is depressed, ignition is on and release button on gearshift lever is depressed. For additional information on shift lock system, see AUTOMATIC TRANSMISSIONS DIAGNOSIS article.
Key lock system prevents ignition switch from being placed in LOCK position unless gearshift lever is in "P" position. Shift lock cable is connected between gearshift lever and ignition switch. When gearshift lever is placed in "P" position, shift lock cable moves lock on ignition switch so ignition switch may be placed in LOCK position.
