Jaguar XJ (X350). Manual — part 1043

TCM Monitoring Functions

As explained above the TCM monitors all input and outputs to identify possible failures. If a fault is

detected the TCM takes the appropriate action to ensure the transmission enters a safe mode of

operation, without sacrificing transmission durability or driver safety.

Supply Monitoring

If the battery voltage is either too great or too low, the TCM will detect a fault condition. For the TCM

to be able to identify this fault, the engine must be running and the transmission fluid temperature

sensor must be functioning correctly.

Solenoid Supply Monitoring

While the solenoid operating transistors are being activated, checks are run for open circuits, shorts

circuits to ground and short circuits to supply. The monitoring function evaluates the voltage

characteristics during the switch on process checking for the above faults.

All solenoid outputs are fully protected. The processor and the appropriate fail-safe action taken can

quickly identify open and short circuit faults.

Sensor Supply Monitoring

The sensor supply voltage is a stabilized supply. This supply is monitored by the micro-processor by

an Analogue to Digital Converter (ADC). If the voltage is out of the valid tolerance a raise a diagnostic

trouble code (DTC) is set and the appropriate fail-safe action is performed.

Electronically Erasable Program Read Only Memory (EEPROM) Monitoring

To diagnose errors with the electronically erasable program read only memory (EEPROM) the TCM

calculates 4 checksums continuously: If the processor identifies discrepancies in any of the four

checksums the TCM will engage mechanical limp-home mode.

The TCM can diagnose errors within the EEPROM. Diagnosis is only performed during TCM

initialization. There is no fail-safe mechanism associated with this function as the EEPROM is mainly

used for the storage of fault codes and transmission calibration adaptions. If a fault occurs the TCM is

able to perform default action and inform the driver of the problem, this is by the instrument cluster

message centre.

Watchdog Monitoring

The watchdog monitoring function has two functions. Firstly it checks that it is possible to inhibit

output control by the activation of the solenoid supply transistor. Secondly the watchdog checks that

the safety circuit is functioning correctly.

During initialization the watchdog checks that it is possible to inhibit control of the pressure regulator

and solenoid valves by switching the solenoid supply transistor. There is a fault if activation of the

solenoids cannot be inhibited by the watchdog (NB. The supply to the solenoids can still be inhibited

by the high side switch responsible for control of each solenoid i.e. One safety path is lost).

Monitoring the Substrate Temperature Sensor

The TCM is situated within the transmission on the valve body. As the TCM controls a number of high

power solenoids and is surrounded by ATF, the TCM can obviously get very hot. If the temperature of

the hardware rises above a pre-determined level the TCM will be shut down. Prior to the TCM

shutting down the TCM will log a fault code, during shutdown the transmission will enter mechanical

limp-home mode. Monitoring of the substrate temperature is performed by a temperature

dependent resistor mounted on the processor.

Plausibility Checking

The TCM detects a fault if an excessive voltage jump is identified between any two consecutive

measurements. Also, with the engine started from cold the transmission fluid temperature will start

to rise. Therefore the substrate or fluid temperature will also start to rise because the TCM is

surrounded by transmission fluid. If the engine and output shaft speed is higher than a set threshold

for a predetermined length of time without the substrate temperature rising above a set threshold a

fault will be detected.

Pressure Regulator/Solenoid Monitoring

Each pressure regulator and solenoid is monitored for open circuits and short circuits. The TCM also

checks that the current being delivered to each solenoid valve or pressure regulator is within valid

limits. When each solenoid is being driven with minimum current the TCM checks that the current is

not above a threshold value. If a solenoid is being driven with maximum current, it checks that the

current is not below a valid threshold. If either of these two errors occurs a plausibility error is logged

and the appropriate fail-safe action is performed.

Output Speed Monitor

It is possible for the TCM to diagnose electrical errors associated with the output speed sensor while

the vehicle is stationary as well as moving. Plausibility monitoring is performed on the sensor output

when the vehicle is moving.

Input Speed Monitor

It is possible for the TCM to diagnose electrical errors associated with the input shaft speed sensor

while the vehicle is stationary as well as moving. Plausibility monitoring is performed on the sensor

output when the vehicle is moving.

Transmission Fluid Temperature Sensor Monitoring

The TCM monitors for faults associated with the transmission fluid temperature sensor in the

following ways:

1 . Open and short circuit fault detection.

2 . The temperature cannot alter by more than a predefined differential between any two

consecutive measurements.

3 . The transmission fluid temperature must rise after the engine has been started provided that the

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fluid temperature was low enough to begin with (The vehicle must be driven and the diagnostic test

condition met).

Position Sensor Monitoring

The TCM can identify errors with the position switch located within the transmission. If an

unrecognized position code is read by the TCM a plausibility fault will be logged. (A code is checked

between positions).

The position switch outputs a 4-bit code to the TCM, the bits being labelled L1-L4. For the

transmission, the following codes are used to identify the selector position.

Only for the automatic side of the J-GATE P,R,N,D

Selector position switch code

Position

Code

L1 L2 L3 L4

Park

0

0

1

0

Reverse 0

0

0

1

Neutral

0

1

0

0

Drive

1

1

1

0

Gear Ratio Monitoring

The gear ratio diagnostic checks that each gear ratio is correctly engaged. Also, following a gear shift

the diagnostic checks that the transmission has engaged the target gear within the allowed time.

Torque Converter Monitoring

The TCM checks that the torque converter can be locked correctly. If torque converter lock-up does

not occur correctly the TCM performs the appropriate fail-safe action of opening the Torque

converter clutch.

Torque Converter Lock-up Control

The TCM controls how the torque converter clutch is engaged as a function of the accelerator pedal

position , output speed, transmission fluid temperature, gear selected and shift program. Lock-up is

possible in all forward gears, but usually it is restricted to fourth, fifth and sixth gears. To make use of

the comfort enhancing effect of the torque converter, the converter clutch can be disengaged prior

to a downshift or up-shift. The torque converter lock up clutch is always modulated to allow for

controlled slip, to further improve the shift quality.

Shift Energy Management

This function involves reducing or increasing the engine output torque during shifting. The aim when

up-shifting is to reduce the energy that is dissipated in the friction elements of the transmission. This

is done by reducing the engine torque during synchronization without interrupting the tractive drive.

This function may be used for:

Increasing the transmission service life by shortening the slipping time.

Improving the shift comfort by reducing the step change in torque caused by the gearshift.

Transferring a higher engine power, this is allowed by the mechanical in-gear strength of the

transmission.

Real-time control of engine torque is required to maintain maximum shift quality and transmission

durability. The TCM has the ability to control the engine output torque during the gearshift to

synchronize with the operation of the transmission clutches.

Pressure Modulation

To provide a high level of shift comfort and durability, the hydraulic pressure in the shift related

friction elements of the transmission must be matched very accurately to the transmission input

torque. This hydraulic pressure is composed of a hydraulically pre-set basic pressure and a controlling

pressure that is set by one of the electro-hydraulic pressure regulators.

The transmission input torque can be directly calculated from the following operating parameters:

engine torque signals, engine speed or any signals transmitted from the ECM by CAN, and converter

slip. Separate pressure characteristics for each gear change make it possible to adapt precisely to the

particular shift operation. A further improvement in shift comfort is achieved by individual treatment

of special cases, such as manual shifts.

Shift Quality Adapts

The shift quality adapts are used to obtain a high quality and consistant shift feel. This is achieved

through monitoring shift quality and then adapting the shift pressures and shift energy management

to overcome hardware variability and "in service wear".

It will typically take a new transmission approximately 161 kilometers (100 miles) of use to fully

adapt.

Shift Point Selection

The gearshift points are selected by the TCM, as a function of the output speed, accelerator pedal

position, selector position and shift program selected. The driver has control over the shift points by

the selector lever, accelerator pedal movement and mode switch.

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