Part 4
Message Center DisplayThe message center is located in the lower center of the instrument cluster. The message center is a LCD to relay vehicle status and operating information to the driver. The message center can display messages relating to a number of the vehicle systems. The following list shows the possible transmission related messages:
^ TRANSMISSION FAULT LIMITED GEARS AVAILABLE
^ TRANSMISSION FAULT AND OVERHEAT
^ TRANSMISSION FAULT
^ TRANSMISSION OVERHEAT
TRANSMISSION CONTROL MODULE (TCM)
The TCM is an integral part of the Mechatronic valve block which is located at the bottom of the transmission, behind the fluid pan. The TCM is the main controlling component of the transmission.
The TCM processes signals from the transmission speed and temperature sensors, engine control module and other vehicle systems. From the received signal inputs and pre-programmed data, the module calculates the correct gear, torque converter clutch setting and optimum pressure settings for gear shift and lock-up clutch control.
The TCM outputs signals to control the shift control solenoid valve and the Electronic Pressure Regulator Solenoids (EPRS) to control the hydraulic operation of the transmission.
The ECM supplies the engine management data on the high speed CAN bus system. The TCM requires engine data to efficiently control the transmission operation, for example-, flywheel torque, engine speed, accelerator pedal angle, engine temperature etc.
The steering angle sensor and the ABS module also supply data to the TCM on the high speed CAN bus system. The TCM uses data from these systems to suspend gear changes when the vehicle is cornering and/or the ABS module is controlling braking or traction control.
The selector lever is connected to the automatic transmission and the position switch in the transmission by a Bowden cable. Movement of the selector lever moves the position switch via the Bowden cable and the switch position informs the TCM of the selected position. The sport/manual +/- Command Shift switch passes manual/sport selections to the TCM. An additional switch provides a selector lever in park position signal. Once the selector lever position is confirmed, the TCM outputs appropriate information which is received by the instrument cluster to display the gear selection information in the message center.
The Mechatronic valve block also contains the speed and temperature sensors. These are integral with the Mechatronic valve block and cannot be serviced individually. The speed sensors measure the transmission input and output speeds and pass signals to the TCM. The fluid temperature sensor is also located in the valve block and measures the fluid temperature of the transmission fluid in the fluid pan.
The TCM is connected to the starter relay coil. When the selector lever is in PARK or NEUTRAL, the module provides a ground for the coil allowing the starter relay to be energized and allow starter motor operation. If the selector lever is in any other position, the module will not provide the ground preventing starter motor operation.
Inputs and Outputs
Connector C01 93
The following table shows the connector pin details for the connector on the transmission.
DIAGNOSTICS
The diagnostic socket is located in the lower instrument panel closing panel, on the driver's side, below the steering column.
The diagnostic socket allows the exchange of information between the various modules on the bus systems and T4 or a diagnostic tool using IS014229 protocol. The information is communicated to the socket via the high speed CAN bus from the TCM. This allows the retrieval of diagnostic information and programming of certain functions using T4 or a suitable diagnostic tool.
The TCM uses a P code strategy which stores industry standard Diagnostic Trouble Codes (DTC) relating to faults.
CONTROLLER AREA NETWORK (CAN)
The high speed CAN broadcast bus network is used to connect the powertrain modules. The CAN bus is connected between the following electronic units:
High Speed CAN Bus
^ TCM
^ Instrument cluster
^ Air suspension module
^ Steering angle sensor
^ Rear differential module
^ Center console switch pack
^ Electric park brake module
^ Restraints control module
^ Engine Control Module (ECM)
^ ABS control module
^ Adaptive front lighting control module
^ Transfer box control module
^ Adaptive cruise control module
^ Diagnostic socket.
The CAN bus allows a fast exchange of data between modules. The CAN bus comprises two wires which are identified as CAN high (H) and CAN low (L). The two wires are colored yellow/black (H) and yellow/brown (L) and are twisted together to minimize electromagnetic interference (noise) produced by the CAN bus messages. For additional information, refer to Communications Network (418-00 Module Communications Network)
In the event of CAN bus failure, the following symptoms may be observed:
^ Transmission operates in default mode
^ Torque converter lock-up clutch control is disabled
^ Gear position indication in instrument cluster message center inoperative (this will also occur with any transmission fault).
DRIVING MODES
There are a number of different driving modes of operation. Some can be selected by the driver and some are automatically initiated by the TCM during driving:
^ Normal mode
^ Sport mode
^ Manual (Command Shift) mode
^ Adaptive Shift Strategy (ASIS)
^ Hill Descent Control (HDC) mode
^ Cruise mode
^ Hill mode
^ Default (Limp home) mode
^ Reverse lock-out mode
^ Cooling strategy.
^ Curve recognition mode
^ Fast off recognition
Normal Mode
Normal mode is automatically selected by the TCM on power up. In this mode all automatic and adaptive modes are active. Normal mode uses gear shift and lock-up maps to allow for vehicle operation which offers fuel consumption and emissions or driveability depending on the driving style. If the transmission is operated in sport or manual mode and the selector lever is moved to the 'D' position, normal mode is automatically resumed.
Sport Mode
The sport mode operates in high range only and provides enhanced acceleration and responsiveness. In sport mode the TCM uses shift maps which allow the transmission to downshift more readily, hold gears for longer at higher engine speeds, and limits the transmission to the first five gears (6th gear is not used).
Sport mode is selected by moving the selector lever to the left into the 'M/S' position. When the sport mode is first selected, 'SPORT' is displayed in the message center for 6 seconds and, if 6th gear is currently engaged, the TCM downshifts to 5th.
Manual (Command Shift) Mode
Manual mode allows the transmission to operate as a semi-automatic 'Command Shift' unit. The driver can change up and down the six forward gears with the freedom of a manual transmission.
Shift maps are provided for manual mode to protect the engine at high engine speeds. The TCM will automatically change up to a higher gear ratio to prevent engine overspeed and change down to a lower gear ratio to avoid engine laboring and stalling.
When kickdown is requested the TCM downshifts at least 2 gears.
When the vehicle is stationary, to drive off the driver can select 1st, 2nd or 3rd gear in low and high range. Any other gear selection will be rejected by the TCM.
When driving off, upshifts can be pre-selected by making + selections with the selector lever for the number of upshifts required. The TCM then automatically performs a corresponding number of upshifts when the appropriate shift points are reached. So, for example, when starting off in 1st gear, if three + selections are made in quick succession, the TCM will automatically change up through the box to 4th gear as the vehicle accelerates, without any further selections being made.
In manual mode a low gear can be selected to provide engine braking for descending a slope without HDC or continuous use of the brake pedal. The driver can prepare for the end of the descent by moving the selector lever to D. The TCM will maintain the low gear and only revert to automatic shift control when the throttle is opened and vehicle speed increases.
Adaptive Shift Strategy (ASIS)
The ASIS system is a new feature on automatic transmissions. With the TCM linked via the CAN bus to other vehicle systems, signals are received which can allow the TCM to calculate the way in which the vehicle is being driven. The type of signals include the following:
^ Longitudinal and lateral acceleration
^ Engine speed
^ Engine torque
^ Oil temperature
^ Accelerator pedal position
^ Wheel speed.
Using these signals, additional transmission control can be obtained. The TCM can calculate when the vehicle is cornering, all wheels are gripping, the driver is braking or if the driver is accelerating. This is the conventional 'Adaptive' transmission control. ASIS uses this system but adds the continuous adaptation of the gear changes to the individual driving style of the driver.
HDC Mode
The HIDC mode assists the ABS module in controlling the downhill speed of the vehicle. When HIDC is selected on, the ABS module selects the most appropriate gear for the descent, to maximize engine braking.
Cruise Mode
When speed control is activated, the TCM receives a cruise active message on the CAN bus. The TCM activates a speed control map which prevents locking and unlocking of the torque converter clutch and minimizes up and down shifts.
Hill Mode
Hill mode is initiated by the TCM when the engine torque, via ECM signals on the CAN bus, exceeds the theoretical load curve for normal operation. The TCM monitors this signal to determine when the vehicle is traveling up or down a steep gradient.
In hill mode the TCM adopts one of four shift maps, three uphill and one downhill. The shift map chosen depends on the severity of the slope as determined from the engine signals and the appropriate gear is selected to assist with the ascent or descent.
Hill mode can also be initiated when the vehicle is at very high altitudes or ambient temperatures, and also when the vehicle is towing.
Default (Limp Home) Mode
If a transmission fault is detected by the TCM, the TCM adopts a limp home mode strategy. 'TRANS. FAILSAFE' is displayed in the message center and, if the fault has an effect on engine emissions, the MIL will also be illuminated.
In default mode, P, R and N functions operate normally (if the fault allows these selections) and the TCM locks the transmission in 3rd or 5th gear to allow the driver to take the vehicle to the nearest dealer. The torque converter lock-up clutch is disabled and reverse lock-out will not function.
If the vehicle is stopped and subsequently restarted in the default mode condition, the TCM operates normally until the fault which caused the condition is detected again.
When limp home mode is active, the gear position indicator will show one of the following letters which defines the fault type:
^ F- transmission is operating in limp home mode
^ 'H' - transmission has reached overheat threshold temperature and transmission is operating in limp home mode
^ 'E'- CAN bus is off and transmission is operating in limp home mode.
If electrical power is lost and the transmission is operating in mechanical limp home mode, the selector lever will not be locked in the 'N' position by the shift interlock solenoid. The lever will be locked in the 'P' position and can only be released by using the interlock emergency release lever or by correcting the electrical fault.
Reverse Lock-Out Mode
When the vehicle is traveling forwards, selecting reverse could cause transmission damage. To protect against this, reverse gear is prohibited if the vehicle is traveling forwards at a road speed above 5 mph (8 km/h).
Cooling Strategy
The purpose of the cooling strategy is to reduce engine and transmission temperatures during high load conditions, when towing a trailer for example. Under these conditions the engine and transmission may generate excessive heat.
If the transmission fluid temperature increases to 125°C (257°F) or higher, the TCM employs the cooling strategy. The message 'TRANSMISSION OVERHEAT 'is displayed in the message center.
The strategy uses a specific shift and torque converter lock-up clutch map. This map allows torque converter clutch lockup and gear shifts to operate outside of their normal operation. This will reduce the engine speed and/or slip in the torque converter, therefore reducing heat generated by the engine and the transmission.
If the transmission fluid temperature increases to 137°C (278°F) or higher, the transmission will use the default (limp home mode). 'H' is displayed in the gear position indicator. If the temperature exceeds 140°C (284°F), CAN bus transmission is disabled and 'E' is displayed in the gear position indicator.
The cooling strategy is canceled when the transmission fluid temperature decreases to less than 120°C (248°F) or below.
Curve Recognition
Curve recognition is activated when high levels of lateral acceleration and/or steering angle are detected via the ABS module and steering angle sensor signals on the CAN bus. When this condition is detected, the TCM prevents the transmission from changing to a higher gear to assist with cornering. When the vehicle completes it maneuver, the transmission will shift to the correct ratio.
Fast Off Recognition
Fast off recognition is activated when the TCM detects that the driver has backed off the accelerator pedal quickly in a 'change of mind' maneuver. This is detected by monitoring for a high level of negative pedal angle from the engine control module signal on the CAN bus. If this condition is detected, the TCM holds the current gear ratio to allow the driver to complete his original action without the need for a downshift. The mode remains active for a predetermined time period or if the driving style remains passive.
Terrain Response TM Mode
If the vehicle has the Terrain Response system fitted, the following additional modes are available.
Grass/Gravel/Snow
When the driver selects the Terrain Response grass/gravel/snow special program with the transfer box in either high or low range, the TCM uses a specific set of shift and torque converter maps to optimize the delivery of torque to the wheels and to minimize wheel slip in these terrains. To assist with the vehicle moving from a standstill, the TCM automatically selects 2nd gear in high range and 3rd gear in low range. This special program is fully integrated with hill mode to enhance vehicle control during ascents and descents.
Mud/Ruts
When the driver selects the Terrain Response mud/ruts special program with the transfer box in either high or low range, the TCM uses a specific set of shift and torque converter maps to optimize vehicle traction in this terrain.
Sand
When the driver selects the Terrain Response sand special program with the transfer box in either high or low range, the TCM uses a specific set of shift and torque converter maps to optimize the tractive performance in sand by holding onto gears longer and downshifting more readily. This mode is fully integrated with the hill mode to further enhance performance during ascents.
Rock Crawl
When the driver selects the Terrain Response rock crawl special program, which is only available with the transfer box in low range, the TCM uses a specific shift map which maximizes torque delivery at slow speeds associated with this type of terrain.
TRANSMISSION FAULT STATUS
If the TCM detects a fault with the transmission system, it will enter a default mode to prevent further damage to the transmission and allow the vehicle to be driven.
When a fault is detected a CAN message is sent from the TCM and is received by the instrument cluster. The instrument cluster illuminates the MIL and displays 'TRANS. FAILSAFE' in the message center.
Some transmission faults may not illuminate the MIL or display a fault message, but the driver may notice a reduction in shift quality.
ENGINE SPEED AND TORQUE MONITORING
The ECM constantly supplies the TCM with information on engine speed and torque through messages on the CAN bus. The TCM uses this information to calculate the correct and appropriate timing of shift changes.
If the messages are not received by the ECM, the TCM will implement a back-up strategy to protect the transmission from damage and allow the vehicle to be driven.
In the event of an engine speed or torque signal failure, the transmission will adopt the electrical limp home mode with the transmission operating in a fixed gear.
TOWING FOR RECOVERY
The following procedure must be used to ensure that the vehicle is towed in a safe condition and damage to the vehicle transmission systems is prevented.
^ Secure the towing attachment from the recovery vehicle to the towing eye of the vehicle to be recovered.
^ Make sure that the hand brake is on. Turn the ignition key to the ignition position 11.
^ Apply the footbrake and move the automatic transmission selector lever to the neutral position. If electrical power is not available, use the manual interlock release tab on the selector lever to move the lever to the neutral position.
^ Make sure that the ignition is in the auxiliary position I or, if the stop lamps and turn signal indicators are required, in the ignition position 11.
^ Make sure that the hand brake is released before the vehicle is towed.
^ The vehicle can only be towed for a maximum of 31 miles (50 km) at a maximum speed of 30 mph (50 km/h). Towing the vehicle for longer distances and/or faster speeds will damage the transmission.
WARNING: Do not remove the key or move the ignition switch to position 'O' when the vehicle is being towed. The steering lock will be engaged preventing the steering from being turned.
CONTROL DIAGRAM
NOTE: A = Hardwired; D= High Speed CAN Bus