Part 3
Automatic Transmission ContinuedDIAGNOSTICS
The diagnostic socket is located in the instrument panel, in the driver's side stowage tray. The socket is secured in the fascia panel and protected by a hinged cover.
Diagnostic Socket
The diagnostic socket allows the exchange of information between the various modules on the bus systems and an approved Land Rover diagnostic system. The information is communicated to the socket via the high speed CAN (controller area network) bus from the TCM (transmission control module). This allows the retrieval of diagnostic information and programming of certain functions using an approved Land Rover diagnostic system.
The TCM (transmission control module) uses a P code strategy which stores industry standard DTC (diagnostic trouble code) relating to faults.
CONTROLLER AREA NETWORK (CAN)
The high speed CAN (controller area network) broadcast bus network is used to connect the powertrain modules. The CAN (controller area network) bus is connected between the following electronic units:
High Speed Bus
^ TCM (transmission control module)
^ 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 (anti-lock brake system) control module
^ Adaptive front lighting control module
^ Transfer box control module
^ Adaptive cruise control module
^ Diagnostic socket.
The CAN (controller area network) bus allows a fast exchange of data between modules. The CAN (controller area network) bus comprises two wires which are identified as CAN (controller area network) high (H) and CAN (controller area network) 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 (controller area network) bus messages.
In the event of CAN (controller area network) 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 (transmission control module) during driving:
^ Normal mode
^ Sport mode
^ Manual (CommandShiftTM) 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 (transmission control module) 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 (transmission control module) 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, if 6th gear is currently engaged, the TCM (transmission control module) downshifts to 5th.
Manual (CommandShiftTM) Mode
Manual mode allows the transmission to operate as a semi-automatic 'CommandShiftTm' 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 (transmission control module) 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 (transmission control module) 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 (transmission control module).
When driving off, upshifts can be pre-selected by making + selections with the selector lever for the number of upshifts required. The TCM (transmission control module) 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 (transmission control module) 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 (transmission control module) 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 (transmission control module) linked via the CAN (controller area network) bus to other vehicle systems, signals are received which can allow the TCM (transmission control module) 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 (transmission control module) 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 HDC mode assists the ABS (anti-lock brake system) module in controlling the downhill speed of the vehicle. When HDC is selected on, the ABS (anti-lock brake system) module selects the most appropriate gear for the descent, to maximize engine braking.
Cruise Mode
When speed control is activated, the TCM (transmission control module) receives a cruise active message on the CAN (controller area network) bus. The TCM (transmission control module) 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 (transmission control module) when the engine torque, via ECM (engine control module) signals on the CAN (controller area network) bus, exceeds the theoretical load curve for normal operation. The TCM (transmission control module) monitors this signal to determine when the vehicle is travelling up or down a steep gradient.
In hill mode the TCM (transmission control module) 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 (transmission control module) , the TCM (transmission control module) 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 (malfunction indicator lamp) will also be illuminated.
In default mode, P, R and N functions operate normally (if the fault allows these selections) and the TCM (transmission control module) 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 (transmission control module) 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 (controller area network) 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 travelling forwards, selecting reverse could cause transmission damage. To protect against this, reverse gear is prohibited if the vehicle is travelling 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 (transmission control module) employs the cooling strategy. An applicable message is displayed in the message center to alert the driver.
The strategy uses a specific shift and torque converter lock-up clutch map. This map allows torque converter clutch lock-up 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 (controller area network) bus transmission is disabled and 'E' is displayed in the gear position indicator.
The cooling strategy is cancelled 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 (anti-lock brake system) module and steering angle sensor signals on the CAN (controller area network) bus. When this condition is detected, the TCM (transmission control module) prevents the transmission from changing to a higher gear to assist with cornering. When the vehicle completes it manoeuvre, the transmission will shift to the correct ratio.
Fast Off Recognition
Fast off recognition is activated when the TCM (transmission control module) detects that the driver has backed off the accelerator pedal quickly in a 'change of mind' manoeuvre. This is detected by monitoring for a high level of negative pedal angle from the engine control module signal on the CAN (controller area network) bus. If this condition is detected, the TCM (transmission control module) 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.
TRANSMISSION FAULT STATUS
If the TCM (transmission control module) 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 (controller area network) message is sent from the TCM (transmission control module) and is received by the instrument cluster. The instrument cluster illuminates the MIL (malfunction indicator lamp) and displays an applicable message in the message center.
Some transmission faults may not illuminate the MIL (malfunction indicator lamp) or display a fault message, but the driver may notice a reduction in shift quality.
ENGINE SPEED AND TORQUE MONITORING
The ECM (engine control module) constantly supplies the TCM (transmission control module) with information on engine speed and torque through messages on the CAN (controller area network) bus. The TCM (transmission control module) uses this information to calculate the correct and appropriate timing of shift changes.
If the messages are not received by the ECM (engine control module), the TCM (transmission control module) 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 II.
^ 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 II.
^ 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 '0' when the vehicle is being towed. The steering lock will be engaged preventing the steering from being turned. With the engine not running, the brake booster and power steering pump will be inoperative. Care must be taken to ensure the vehicle is maneuvered and driven accordingly.