Ford Workshop Service and Repair Manuals

Transmission control unit

Installation position.

The transmission control unit is integrated into the clutch actuator.

The assembly is located in the engine compartment in front of the transmission and is attached to the left-hand front longitudinal member.

The transmission control unit is connected to the vehicle wiring harness via two encoded connectors.

Function

The transmission control unit is responsible for detecting the incoming signals from the individual sensors and control units. It must then evaluate these signals and perform the necessary gearshifts.

In the process the transmission control unit controls every aspect of the gearshift.

• Engine torque reduction
• Disengagement of the clutch
• Selection of the target gear
• Synchronisation
• Engagement of the target gear
• Engagement of the clutch
• Engine torque increase

The transmission control must perform the gearshift in a way that does not adversely affect the long-term durability of the transmission.

Diagnosis

The transmission control can be diagnosed with WDS via the DLC.

The DLC is located in the passenger compartment underneath the steering wheel.

The transmission control unit can be reprogrammed with WDS if a new calibration becomes necessary.

Gearshift strategies

Park

The clutch is engaged when the engine is switched off.

If the selector lever is not in N, then a gear is engaged to prevent the vehicle from rolling away.

Engine start release

The engine start is only permitted if the PCM has received a start release from the transmission control unit via the CAN databus.

The following conditions must be satisfied for this to happen:

• Transmission in neutral
• Selector lever in neutral
• Brake pedal depressed

Adaptation of the clutch touch point

NOTE:If a new clutch actuator with integrated transmission control unit is installed then the touch point of the clutch needs to be relearned with the aid of WDS.

The term 'clutch touch point' describes the point at which the pressure plate and the clutch plate touch and transmit a low torque (approx. 4 Nm).

The transmission control unit needs this information to be able to always engage the clutch in the best possible way, i.e. smoothly without judder and without excessive slip.

In the factory the clutch touch point is stored in the non-volatile memory of the transmission control unit.

The adaptation of the clutch touch point is performed repeatedly while driving with the engine idling, with a gear engaged and with the brake depressed.

In addition, the current clutch touch point is checked by the transmission control unit during a gearshift and then adapted as required.

This means that the various tolerances in the clutch operating mechanism, which arise for example due to variations in operating temperatures, are continuously adapted and optimised for the current operating conditions.

Creep

The system offers a creep function similar to that found on an automatic transmission whenever the selector lever is in position D or R and neither the accelerator pedal or the brake pedal are depressed.

The creep function means that when first gear or reverse gear is engaged the clutch is partially engaged (i.e. with slip) and a noticeable amount of torque is transmitted.

The creep quality depends greatly on the smoothness of the engine when idling.

The creep function is suspended if there is not enough torque available to move the vehicle (e.g. when climbing hills) or if the torque signal transmitted by the PCM is not precise enough.

Stalling of the engine is prevented in all cases.

NOTE:If the engine does stall then this indicates a fault. This type of fault could be caused by a problem in the engine management as well as a problem in the transmission control.

If the driver's door is open while the creep function is active then a warning sounds and the current gear is flashed on the instrument cluster display.

The creep function is switched off when the parking brake is applied.

Torque tracking

The clutch is only operated as far as is required by the current torque which is to be transmitted.

The clutch torque is a function of engine torque, engine speed and transmission input speed (calculated back from the rotational speeds of the wheels).

The advantage of torque tracking is that the time required to operate the clutch during gearshifts is significantly reduced.

Another advantage of torque tracking is that the clutch can temporarily slip whenever there are torque peaks.

This effect places no particular strain on the clutch because there is only a small difference in rotational speeds at this point. However, it offers the advantage of smoother ride comfort, as any judder in the powertrain is absorbed by the clutch slip.

Clutch overheating protection

In order to protect the clutch against overheating, it is necessary to deduce the current clutch temperature.

The transmission control unit can use the current clutch temperature to identify faults, enable warnings to be given out and modify the control strategy if the clutch temperatures are too high.

No separate temperature sensor is installed for measuring the clutch temperature. Instead, the clutch temperature is calculated by the transmission control unit.

To do this it uses the following factors:

• Ambient temperature (from the engine management),
• Time since engine start,
• Previous clutch slip,
• Torque to be transmitted.

The calculated clutch temperature is compared to the characteristic clutch temperature capacity stored in the control unit, which is taken as the limit value.

If the driver attempts to hold the vehicle with clutch slip (e.g. when climbing a hill), then this will result in a risk of the clutch overheating.

In situations like this the transmission control deliberately encourages judder by varying the amount of clutch torque to be transmitted (more or less clutch slip).

This warns the driver about the imminent risk of overheating.

The driver's response to this will either be to release the accelerator pedal (and therefore disengage the clutch) or to depress the accelerator pedal (and therefore ensure slip-free engagement of the clutch).

If however the driver fails to react to this then it may lead to destruction of the clutch disc.

In order to protect the clutch against overheating while driving, torque tracking is no longer performed above a certain temperature.

In these cases this means that the clutch is always fully engaged (which results in longer gearshift times).

If the vehicle stops while the risk of the clutch overheating is still present then the creep function is disabled.

Pulling away from standing

CAUTION:It is possible to depress both the accelerator pedal and the brake pedal at the same time. If this happens then the clutch is subjected to severe strain and can be destroyed.

NOTE:The driver controls pulling away with the accelerator pedal alone.

In principle, it is possible to pull away in 1st, 2nd and reverse gear.

In automatic driving mode the vehicle will only pull away from standing in 1st gear.

If the driver specifically wishes to pull away in 2nd gear, then the 2nd gear can be selected in manual driving mode.

If the vehicle is already rolling, then the corresponding gear is automatically selected by the transmission control in both driving modes.

In order to ensure that the vehicle does not pull way inadvertently, the selected gear is only engaged if the brake is depressed when the selector lever is moved from N to D or R.

The gear is also not engaged if the accelerator pedal is not depressed within approx. 26 seconds of shifting the selector lever (from N to D or R).

Driving down a steep descent

The transmission control detects that the vehicle is driving down a steep descent by comparing the current data for vehicle acceleration and engine load.

If the transmission control detects that the vehicle is driving down a steep descent then it prevents upshifts below a certain engine speed to maximise the benefits of engine braking.

In addition, the transmission control shifts down a gear when the brake pedal is depressed provided this is permitted by the engine speed.

Detection of driving resistance

The transmission control detects a driving resistance (e.g. climbing a hill or towing a trailer) by comparing the current data for vehicle acceleration and engine load.

The transmission control selects the gearshift timing according to the magnitude of the driving resistance.

The aim is to avoid frequent gearshifts back and forth between the gears.

Detection of fast off mode

A 'fast off' situation is recognised when the accelerator pedal is suddenly released.

In this case the system suppresses an immediate upshift to the next higher gear in order to give the driver a more direct driving experience and to maximise the benefits of engine braking.

Cornering detection

The transmission control system detects cornering by comparing the wheel speed sensor signals from the two non-driven wheels.

Depending on the detected difference in speed, upshifts are prevented during cornering in order to avoid tip in/tip out reactions.

Engagement of reverse gear

For safety reasons it must not be possible to accidentally engage reverse gear by inadvertently moving the selector lever to the "R" position.

Therefore reverse gear will only be engaged under the following conditions:

• Electronic selector lever in position "R"
• Vehicle speed below 2 km/h
• Time-delayed to ensure that the differences in rotational speeds are not too high
• Brake pedal depressed

One exception is fast changes between D » N » R and R » N » D, for example when attempting to unstick the vehicle in snow. In this case the transmission control will accept the gear change to R without depressing the brake pedal in between.

Manual driving mode

In manual driving mode the driver can decide when to change gear.

However, the transmission control checks first whether the engine speed would be too high or low after the gear change before carrying out the gear change.

The system also changes gear automatically in manual driving mode if the engine speed becomes too low for the selected gear (when the vehicle is decelerating).

If the driver operates the selector lever several times in quick succession then the target gear is engaged without the intermediate gears being engaged.

If the expected engine speed (too high or too low) prevents the target gear from being engaged, then the transmission control shifts up to the next available and appropriate gear.

It is possible at any time to change between automatic and manual driving modes.

Towing

The vehicle can be towed with the transmission in neutral.

NOTE:Battery voltage must be present at the transmission control unit to ensure that the transmission control releases the clutch to shift into neutral.

If the engine is not running then the following requirements must be met for the shift into neutral to take place:

• Ignition key in position II
• Brake pedal depressed
• Selector lever in position "N"

Signal transmission on the CAN databus

Engine start release

The PCM receives an engine start release signal from the transmission control unit if the transmission and the selector lever are in neutral and the brake pedal is depressed.

Engine speed

The engine speed is detected by the Crankshaft Position (CKP) sensor and passed on to the PCM.

The engine speed is transmitted from the PCM via the CAN databus to the transmission control unit.

The transmission control unit uses this signal for:

• Engagement and disengagement of the clutch
• Adaptation of the clutch touch point
• Torque tracking
• Creep function
• Clutch overheating protection
• Determination of the target gear

Engine load

The PCM determines a load signal, which is transmitted via the CAN databus to the transmission control unit.

The transmission control unit uses this signal for the following functions:

• Determination of the gearshift timing
• Torque tracking
• Creep function
• Clutch overheating protection
• Detection of hill descent
• Detection of driving resistance

Signal for torque increase/decrease

Before the transmission control unit disengages the clutch, it sends a signal to the PCM to reduce the torque.

After the PCM has reduced the engine torque, the transmission control unit disengages the clutch, disengages the selected gear, shifts into the target gear and re-engages the clutch again.

Afterwards the transmission control unit sends the PCM a signal to increase the torque.

The PCM then increases the engine torque.

Wheel speed signals

The ABS wheel sensors supply a separate wheel speed signal for each wheel to the ABS control unit.

These wheel speed signals are transmitted via the CAN databus to the transmission control unit.

The transmission control unit uses the wheel speed signals for:

• Determining the vehicle speed
• Determining the vehicle acceleration
• Cornering detection

Selector lever position and operation

The current selector lever position or the current selector lever operation is detected by the electronic selector lever by means of six Hall sensors with integrated electronic circuitry and is transmitted via the CAN databus to the transmission control unit.

The transmission control unit uses the current selector lever position or the current selector lever operation for determination of the gearshift timing in manual or automatic driving mode.

Brake pedal position signal

The PCM receives a signal from the brake pedal switch which indicates whether or not the brake pedal is currently depressed.

This signal is transmitted by the PCM via the CAN databus to the transmission control unit.

The transmission control unit uses the brake pedal actuation signal for:

• Engine start release
• Hill descent mode
• Engagement of reverse gear

Parking brake actuation signal

The signal from the parking brake lever switch is detected by the instrument cluster and transmitted via the CAN databus to the transmission control unit.

The signal is used by the transmission control unit for switching off the creep function when the parking brake is activated.

It is possible to pull away on a hill with the parking brake applied if the accelerator pedal is depressed in addition to the applied parking brake.

Gear display

The transmission control unit sends the information about the currently engaged gear and the current driving mode (automatic or manual) on to the instrument cluster.

The instrument cluster displays both the engaged gear and the automatic driving mode (Auto) for the driver.

During a gearshift the last engaged gear remains displayed until the gearshift is complete.

If the gear display flashes while the vehicle is stationary, then this means that the selected gear has not yet been engaged, as not all of the required conditions (e. g.: R selected, brake pedal not yet depressed) are satisfied.

If the gear display flashes and a warning tone sounds at the same time, then this is warning the driver that the creep function is active while the driver's door is open.

If the gear display flashes while driving and the MIL warning lamp comes on at the same time, then this indicates a fault in the transmission control system.

If "--" is displayed while driving and the MIL warning lamp is on, then there is a communications fault to the transmission control unit.

Actuation of the MIL warning lamp

The MIL warning lamp is actuated by the instrument cluster in the event of a serious fault with the transmission. The information required to actuate the MIL warning lamp is sent by the transmission control unit to the instrument cluster.

Warning tone request

The transmission control unit sends a warning tone request to the instrument cluster if the following conditions are met:

• Engine running
• Transmission control in creep function
• Driver's door open

The instrument cluster passes on the warning tone request to the GEM. The GEM generates the warning tone.

Clutch actuator distance sensor.

The clutch actuator distance sensor is integrated into the clutch actuator.

It is designed as a solenoid plunger sensor.

The rotary motion of the worm gear is initially converted via the connecting bolt to a linear motion of the ferrite core.

The movement of the ferrite core is detected by the multi-chamber coil of the distance sensor and passed on as a signal to the transmission control unit.

With the distance signal of the clutch actuator, the transmission control unit can determine the exact position of the clutch and thus realise the engagement and disengagement of the clutch, as well as the torque tracking and the creep function of the clutch.

Selector motor distance sensor and shift motor distance sensor

The distance sensors of the selector motor and shift motor are integrated into the motors.

The electric motors are each equipped with ten pairs of magnetic poles.

Two Hall sensors with integrated electronic circuitry are arranged above each of these pairs of poles.

The integrated electronic circuitry of the Hall sensors is capable of using the signals from the two Hall sensors to determine the rotational speed, the rotary angle and the direction of rotation of each electric motor.

The transmission control unit needs the signals to be able to carry out the selection and shift processes precisely.

Brake pedal switch and stoplamp switch

The brake pedal switch and the stoplamp switch are located on the brake pedal.

For safety reasons the transmission control unit receives two signals about the brake pedal position.

When the brakes are operated the stoplamp switch does two things. Firstly it switches on the stoplamps, and secondly it passes the signal directly on to the transmission control unit.

The brake pedal switch opens in the same moment as when the stoplamp switch closes, and in doing so interrupts a ground connection to the PCM.

The signal from the brake pedal switch is transmitted by the PCM via the CAN databus to the transmission control unit.

The transmission control unit needs the information regarding the operation of the brake pedal for:

• Engine start release
• Downshifts during hill descents
• Engagement of forwards and reverse gears when pulling away from standing
• Switching off the creep function
• For adaptation of the clutch touch point

Driver's side door contact switch

The door contact switch is located in the door lock on the driver's side.

When the door is closed a ground connection is signalled to the transmission control unit.

When the door is opened this ground connection is interrupted.

The transmission control unit uses the signal from the driver's side door contact switch to warn the driver if the engine is running, the transmission is in creep mode (no operation of the brake) and the driver's door is open.

In this case the transmission control unit transmits the warning tone request via the CAN databus to the instrument cluster. The instrument cluster forwards this request on to the GEM , and a warning tone is generated by the GEM .

Clutch actuator

The clutch actuator with integrated transmission control unit is located in the engine compartment in front of the transmission and is secured on the left-hand front longitudinal member.

The transmission control unit controls the DC motor in the clutch actuator as required.

The DC motor drives the worm gear via the drive worm gear.

The worm gearing is a self-locking device, as a result of which the piston of the clutch master cylinder will remain naturally in any position without any energy needing to be expended to keep it there.

The worm gear is connected to the piston rod via the piston rod connecting bolt.

Pressure is built up in the clutch master cylinder via the piston rod and the piston.

Brake fluid is used as the hydraulic fluid.

The system does not have its own separate reservoir, but instead is also connected to the reservoir for the brake system.

The afterrun connection serves to supply the clutch actuator with brake fluid and to compensate for the heat-induced expansion of the brake fluid.

The pressure is passed on via the high-pressure line to the clutch slave cylinder in the transmission and the currently requested clutch position is adopted.

Selector motor and shift motor in the shift actuator

The selector motor is actuated by the transmission control unit to select the desired shift slot.

The shift motor is actuated by the transmission control unit to engage the desired gear.

For this purpose the two motors are mechanically connected to the selector shaft of the transmission via relay levers and connecting linkage.

Both motors act via a worm gear to allow the high forces which are required for the gearshift operation to be applied.

The gearing of the shift motor also has an additional elastic module which has the task of making the gearshift as smooth and judder-free as possible and is also designed to keep the gearshift time as short as possible.

Both electric motors are DC motors with two Hall sensors and integrated electronic circuitry each.

The transmission control unit actuates the motors electrically via pulse-width modulated (PWM) signals.

The motors are connected to the wiring harness via coded connectors to prevent any confusion.