BMW Automatic Transmission Gearbox Workshop Manual

2 Electronic Transmission Control Table of Contents Subject Page Adaptive Features ................................................................................ 38 Driver Influenced Features ..................................................................... 39 Environmentally Influenced Features ...................................................... 40 CAN Bus Communication ....................................................................42 Diagnosis and Troubleshooting ...........................................................46 Estblishing a Diagnostic Plan .................................................................47 Fault Codes ...........................................................................................48 Identification Page .................................................................................49 Diagnostic Program ...............................................................................50 Test Modules ..........................................................................................51 Diagnostic Tips ......................................................................................52 Information Resources ...........................................................................53 TCM Coding and Programming ...........................................................54 Transmission Fluid Information ...........................................................56 Transmission Fluid Checking Procedures ...............................................57 Transmission Fluid Application ...............................................................58 Transmission Service ............................................................................59 Transmission Tools ...............................................................................60 Review Questions .................................................................................66 Electronic Transmission Control

38 Electronic Transmission Control Adaptive Features (AGS) AGS features were introduced in 1994 with the A5S560Z transmission. AGS control consists of adaptive features that will modify transmission operation according to various fac- tors. AGS operation can be influenced by two major functional groups: • Driver influenced features (influenced by throttle and kickdown input) • Environmental influences (such as road conditions - icy, traffic etc.) The 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 driving habits.

39 Electronic Transmission Control Driver influenced features of AGS The adaptive drive program is based primarily on throttle input. The throttle information comes from the ECM (DME) via the CAN bus. The TCM continuously monitors the throttle input for: • The current throttle position • The rate of change in pedal movement • The number of acceleration requests • The number of kickdown requests Drive away Evaluation The AGS system selects the appropriate shift program based on the amount of acceleration that occurs during takeoff. When driving away under full throttle the transmission will shift from XE to E. Kick Fast Feature Based on these inputs, the AGS will select one three different driving programs as follows: • Extreme Economy - Shift points are a low speeds for maximum comfort and economy • Economy - The shift points are raised for more performance with economy as priority • Sport - The shift points are higher to take advantage of full engine performance. Under full throttle acceleration at high speed, single gear downshifts are possible. A two gear downshift is possible if the accelerator pedal is moved quickly to kick-down. The Extreme Sport program was eliminated as part of the kick-fast feature.

40 Electronic Transmission Control Environmentally influenced AGS features STOP and GO The feature is activated by 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 occurs, the transmission will stay in second gear. The AGS control has recognized stop and go driving and this function will prevent excessive shifting during heavy conditions. The second gear start will be cancelled when: • The vehicle speed exceeds 40 MPH • The throttle pedal is pressed more than 90% • The range selector is moved to Park, Neutral, Reverse or Sport (4,3 or 2) • The vehicle is in Sport Mode Winter Drive Program This feature is activated when the TCM detects slippage at the rear wheels by comparing front and rear wheel speed signals. When slippage is detected by the TCM, the transmission will start in second gear and the shift points will be lowered. This will reduce torque to the rear wheels allowing improved driveability and traction on slippery roads.

41 Electronic Transmission Control Hill Recognition Program There are two hill recognition programs, one for Uphill and one for Downhill. The TCM will activate this feature when it receives a high engine load signal at slower road speeds. The TCM will perceive this information as being consistent with climbing a hill. The shift points will be raised to prevent constant up and down shifting. This is referred to as the pendulum shift effect. When driving downhill, road speed will increase with minimal throttle input. The TCM will detect a downhill situation and hold the current gear to prevent an upshift when going downhill. Curve Recognition This feature will inhibit upshifts when the vehicle is in a curve. This is to improve stability when the vehicle is cornering at high speeds. The TCM will initiate this feature when it detects a difference between left and right (front) wheel speed signals. The difference in these signals will indicate that the vehicle is in a curve. Be aware that improper tire sizes, brands and inflation pressures can influence this feature. Always address these issues first when diagnosing delayed upshift complaints. Cruise Control Drive program A special cruise control shift map is selected by the TCM when cruise control is active. The TCM will prevent unwanted locking and unlocking of the torque converter clutch. Also, upshifting and downshifting will be minimized. Depending upon application, the cruise control interfaces with TCM via a single wire data link or as on vehicles with electronic throttle control, the TCM will interface with the ECM (DME). Manually Selected “Extreme Sport” Program This feature is activated by moving the shift lever to position 4, 3 or 2. This activates the “Extreme Sport Program” where the shift points are raised for maximum rpm and performance. On Steptronic equipped vehicles, the sport program is obtained by moving the shifter to the manual gate to initiate the “Sport Program”. Modifications to AGS features Since the introduction of AGS features in 1994, there have been some software changes to address customer concerns. Some AGS features have been perceived by the customer as malfunctions. To correct this, some of the AGS features were modified with updated software. The AGS features previously discussed in this text reflect the updated modifications. Always refer to the latest Service Information Bulletins for more information on AGS features.

42 Electronic Transmission Control CAN Bus Communication The CAN bus is a serial communications bus in which all connected control units can send as well as receive information. Data over the CAN bus operates at a rate of up to 1Mb/s (megabits per second). The CAN protocol was developed by Intel and Bosch in 1988 for use in the automotive industry to provide a standardized, reliable and cost-effective communications bus to com- bat the increasing size of wiring harnesses. The CAN bus was originally introduced on BMW automobiles in the 1993 E32 740i/IL as a data link between the TCM (EGS) and the ECM (DME). On earlier EGS systems, various signals were transmitted on individual signal wires. This reduced reliability and increased the amount of wiring needed. The CAN bus allows faster signal transmission and increased versatility. For example, the signals listed in the chart below were previously transmitted on individual wires, now these signals are all on the CAN bus. This chart represents only some of the signals on the CAN bus, there are many more signals transmitted between the TCM and ECM. Sender Information Item Receiver Signal Use ECM Engine Temperature TCM Shift Point Calculation ECM Engine Load (tL) TCM Shift Point Calculation ECM Engine RPM (TD) TCM TCC Slippage ECM Throttle Position (DKV) TCM Shift Point Calculation ECM A/C Compressor ON TCM Fine tune shift points to compensate for increased engine load. TCM Transmission Range ECM Engine Idle Speed Control TCM Torque Reduction Signal (ME) ECM Timing Retard during shifts. TCM TCC Lockup Status ECM Engine Timing Map adjustment. Bi-Directional Data

43 Electronic Transmission Control CAN Bus Topology The CAN bus consists of two twisted copper wires. Each wire contains an opposing signal with the exact same information (CAN-High, CAN-Low). The opposing signals transmitted through the twisted wire serve to suppress any electrical interference. Early CAN bus wiring included a grounded shield around the two wires, later vehicles discarded the shield in favor of the unshielded twisted pair wiring. Due to the linear structure of the network, the CAN bus is available for other modules in the event of a disconnected or failed control unit. This is referred to as a “Tree” structure with each control unit occupying a branch. As previously mentioned, the CAN bus initially was used as a high speed communication link between the DME and AGS control units. With the introduction of the E38 750iL (95 M.Y.), the CAN bus was expanded to include the EML and DSC control modules. The 750iL made exclusive use of the “star coupler” to link the individual CAN bus ends to a common connector. The 1998 model year introduced new users of the CAN bus. The instrument cluster and the steering angle sensor were linked to expand the signal sharing capabilities of the vehicle. The 1999 750iL was the last vehicle to use the shielded cable, after which the entire CAN bus went to twisted pair wiring. Note: Always refer to the proper ETM to determine the exact wiring configuration for a specific model.

44 Electronic Transmission Control On models that use twisted pair, the wire color of the CAN bus is uniform throughout the vehicle with: CAN-Low GE/BR and CAN-High GE/SW or GE/RT. Shielded wiring is easily identified by the black sheath surrounding the CAN bus. Troubleshooting the CAN Bus The failure of communication on the CAN bus can be caused by several sources: • Failure of the CAN bus cables. • Failure of one of the control units attached to the CAN. • Failure of the voltage supply or ground to individual modules. • Interference in the CAN bus cables. Failure of the CAN bus cables The following faults can occur to the CAN bus wiring: • CAN-H/L interrupted • CAN-H/L shorted to battery voltage • CAN-H/L shorted to ground • CAN-H shorted to CAN-L • Defective plug connections (damaged, corroded, or improperly crimped) In each instance, the connected control units will store a fault due to the lack of information received over the CAN bus. On most current models the CAN bus pro- vides data exchange between the following control modules: • ECM (DME) • EML (750iL E38) • TCM (EGS) • IKE/Kombi • ASC/DSC • LEW

45 Electronic Transmission Control The voltage of the CAN bus is divided between the two data lines: CAN-High and CAN-Low for an average of 2.5V per line. The voltage measurement is taken from each data line to ground. Each module on the CAN contributes to this voltage. The fact that 2.5V are present does not mean that the CAN bus is fault free, it just means that the voltage level is sufficient to support communication. Terminal Resistors: are used in the CAN bus circuit to establish the correct impedance to ensure fault free communication. A 120 Ohm resistor is installed in two control units of the CAN between CAN-H and CAN-L. Because the CAN is a parallel circuit, the effective resistance of the complete circuit is 60 Ohms. On some vehicles there is a jumper wire that connects the two parallel branches together, others have an internal connection at the instrument cluster. The resistance is measured by connecting the appropriate adapter to any of the modules on the CAN and measuring the resistance between CAN-L and CAN-H. The resistance should be 60 Ohms. The CAN bus is very stable and can continue to communicate if the resistance on the CAN bus is not completely correct; however, sporadic communication faults will occur. The terminal resistors are located in the ASC/DSC control unit and either the instrument cluster or in the DME. Early 750iL vehicles that used the star connector have a separate external resistor which connect CAN-H and CAN-L together. Modules which do not have the terminal resistor can be checked by disconnecting the module and checking the resistance directly between the pins for CAN- H and CAN-L. The value at these control units should be between 10kOhms and 50kOhms. Print Multimeter End Oscilloscope setting Change Counter Services Help Stimulators Preset measurements BMW Test system Multimeter Measurement Function Measurement Connection Measurement Kind Measurement Range 10 0 10 Resistance Resistance Ohm Ohm Temperature C o Temperature C o Voltage Voltage V V Current Current MFK 1 MFK 1 MFK 2 MFK 2 Current Current Current Current Diode test Diode test Pressure Pressure 2A 2A 50A 50A 1000A 1000A bar bar -|>|- -|>|- Current probe Current probe Pressure Sensor Pressure Sensor Temperature Sensor Temperature Sensor Freeze image Freeze image 2nd measurement 2nd measurement System voltage Rotation speed System voltage Rotation speed Stimulate Stimulate Minimum Maximum Minimum Maximum = Effective value Effective value automatic automatic ± 10 V ± 10 V 2.35 V 2.65 V

46 Electronic Transmission Control Diagnosis and Troubleshooting Due to the cost and complexity of today's electronic transmissions, BMW recommends that the technical hotline be contacted before any repairs are performed. It is important that the technician perform some basic diagnostic procedures before contacting technical assistance. The following procedures should be followed: • Always Verify customer complaint, make sure the complaint is not related to normal operation. (i.e. Warm Up Phase, AGS operation etc.) • Survey Fault Memory - Perform complete quick test. There may be other systems that interface with EGS that could cause faults. (i.e DME, ASC/DSC, IKE/Kombi etc.) • Print out all fault code with fault conditions. Also print out copy of Identification page and diagnostic report. • CHECK TO SEE IF THERE ARE ANY SERVICE BULLETINS THAT APPLY TO YOUR SPECIFIC COMPLAINT. THIS INCLUDES THE SERVICE ROUNDTABLE. • Ensure that battery voltage is sufficient. Battery voltage must be greater than 12.5 with ignition switched off. Check battery connections for tightness and condition. • Check ground connections. (chassis to engine, grounds to bulkhead and shock tower.) • Check over vehicle to look for transmission leaks, physical damage, loose connections etc. • If necessary, check fluid level and condition using DISplus or GT-1. • Check to see if any aftermarket or performance components have been installed that could effect transmission operation. (DME or EGS software as well as any engine modifications). • Check repair history to see if there were any recent repairs that could effect the proper operation of the transmission (i.e. Engine replacement with damaged dowel pin etc.). • Check DCS for any open campaigns or recalls pertaining to drivetrain. • Check and record chassis number, production date and transmission serial # before contacting technical assistance.

BMW Automatic Transmission Gearbox Workshop Manual

You're Reading a Preview

Recently Viewed