Adaptive Transmission Control
AGS (Adaptive Transmission Control)
- The A5S 440 Z is equipped with the AGS 8.55, adaptive transmission control system. The acronym comes from the German name "Adaptiv Getriebesteurung", meaning "Adaptive Gearbox Control".
- The system automatically selects one of several different driving programs based on the driving style and road/environmental conditions. Advantages of the AGS shift control include:
^ Shift program adapted to the driving style
^ Improved safety - No unwanted UP/DOWN shifting while driving through curves.
^ Automatic detection and selection of winter program for better traction.
AGS Program Structure
- AGS as an electronic control logic for automatic transmissions was introduced with the 1994 model year E34s equipped with the M60 engine. Several changes have occurred to the control logic since its introduction due to customer feedback on ride comfort and shift quality.
- To understand AGS and its features as it applies to the A5S 440 Z a distinction has to be made between Pressure Adaptation and Adaptive Transmission Control. This applies to all vehicles equipped with the AGS control.
Pressure Adaptation
- Pressure Adaptation has been a feature of the automatic transmission since the 4HP 22EH. The purpose of this pressure adaptation is to adjust the internal hydraulic pressures in the transmission continuously to maximize the shift comfort.
- This adaptation is carried out automatically regardless of driving styles or driving habits. Pressure adaptation is essentially a separate function from the adaptive transmission control (AGS). This pressure adaptation value is stored in the control module and clearing the adaptation with the diagnostic tester clears this value ONLY.
- It does not have any effect on the adaptive transmission control system.
Adaptive Transmission Control
The ACS can be broken down into two functional groups.
1. Driver controlled features,
2. System features that react automatically to the vehicle's operating conditions.
Driver Controlled Features Of AGS
The adaptive drive program is based primarily on throttle input. The AGS control module continuously monitors the throttle input for:
^ The current pedal position
^ The rate of change in pedal movement
^ The number of acceleration requests
^ The number of kickdown requests
Based on these inputs, the AGS will select one of three different driving programs as follows:
^ Extreme Economy - Shift points are at low speeds for a comfortable ride
^ Economy - The shift points are raised for more engine performance
^ Sport - The shift points are higher to take advantage of full engine performance (Pressing kickdown will result in the selection of the sport drive program).
- This driving program selection is not adapted on a long term basis - nor is it stored in the control module memory when the ignition is switched off. It continually changes as the driver of the vehicle changes his driving habits.
AGS Features That React To Operating Conditions
STOP AND GO - feature is activated by a defined sequence of shifts which are as follows:
^ Upshift from first to second - followed by a downshift from second to first - followed by another upshift from first to second. This is then followed by the vehicle coming to a complete stop.
After this sequence, the transmission will stay in second gear. The AGS control has recognized stop and go driving and this function will prevent excessive shifting during the heavy traffic conditions. This second gear start will be canceled when:
^ The vehicle speed exceeds 40 MPH
^ The throttle pedal is pressed more than 90 %
^ The range selector is moved to "P" "N" or "R"
CURVE RECOGNITION - feature is activated when the AGS control module receives different wheel speed inputs from the left and right sides. During this condition, the AGS inhibits upshifts until the vehicle is traveling straight again. The purpose of this feature is to improve stability while the vehicle is cornering at higher speeds.
WINTER DRIVE PROGRAM - feature is activated when the AGS control module detects slippage at the rear wheels. In the winter program, the transmission will start in second gear and the shift points are lowered. The purpose of this program is to improve the driveablity of the vehicle with slippery road conditions.
Non-AGS Functions
- The following features are part of the automatic transmission control system - but not AGS specific control features. They are carried over from earlier transmission control systems.
HILL RECOGNITION PROGRAM - the control module activates this feature when it receives a high engine load signal at slower road speeds. When the vehicle is traveling up hill the shift points are raised to prevent a "pendulum shift effect" of up and down shifting.
CRUISE CONTROL DRIVE - A special cruise control shift map is activated to prevent pendulum locking and unlocking of the torque converter while cruise control is activated.
MANUALLY SELECTED SPORT PROGRAM - feature is activated by moving the shift selector to "4", "3" or "2" . This activates the Extreme Sport shift program where the shift points are raised to provide maximum engine performance.
ENGINE WARM UP CYCLE - Depending on ambient temperature, the shift points are raised on a cold engine start up. This is designed to speed up the warn up cycle of the engine.
Image Legend:
X = active (pressure build up)
- = inactive (pressure drain)
Electro-Hydraulic Control
Solenoid Valve Operation (output control)
- Similar to the A5S 560 Z, the A5S 440 Z uses shift solenoid valves and pressure regulator valves for shift control as shown in the chart below.
- Three solenoids MV1 MV2 and MV3 are strictly ON/OFF type valves used to control the hydraulic pressure flow in the valve body.
- Three pressure regulator valves, EDS2, EDS3 and EDS5 are used for the so-called "Overlap Control" during shifting. The pressure regulator valves are used to apply pressure, to various clutches and brakes, during shifting, while at the same time pressure is draining from other clutches. This provides for smooth shifting because the delay time from one gear engagement to another is reduced.
- Pressure regulator valve EDS1 is used to regulate the main line pressure used for shift control. Pressure regulator valve EDS4 is used for controlling the lock up clutch in the torque converter. All pressure regulator valves are controlled with a pulse modulated signal.
- The chart shows the solenoid, EDS and clutch application chart for the A5S 440 Z transmission.
Diagnosis/Troubleshooting
- Starting with the 1996 model year, all electronic transmission control falls under the OBD II emission regulations. Any fault with the transmission that will effect tailpipe emissions must be recognized and stored in the OBD II memory. In addition to the transmission failure warning, the Check Engine Lamp must also illuminate when the criteria for OBD II recognition is satisfied.
- Though, BMW system diagnosis and troubleshooting is performed using the DIS and MoDiC, this system can be readout by an independent Service Center using an OBD II compatible Scantool.
Faults that fall under the OBD II criteria include:
^ CAN line
^ AGS power supply
^ Transmission range selector switch
^ Output speed sensor
^ Turbine speed sensor
^ Torque converter clutch
^ Shift solenoid valves (MVs)
^ Pressure regulator valves (EDSs)
- All BMW Diagnosis and troubleshooting is carried out using the DIS or MoDiC with the most recent diagnostic software.
The following information is available on The diagnostic software:
^ Control module identification
^ Fault symptom troubleshooting
^ Status displays
^ Component activation
^ Component testing procedures
^ Special functions and information