Electronic Control Systems

To permit exact determination of the gear-change and lock-up engagement points based on the selected driving mode, the Transmission Control Module (TCM) receives information about the following:

- Selected gear - from gear-shift position sensor (8).
- Selected driving mode - from the mode selector (11).
- Road speed - from the Vehicle Speed Sensor (VSS) (17).
- Transmission input shaft rpm - from transmission speed sensor (5).
- Engine rpm and load - the fuel injection system control module (18).
- Throttle opening - from the fuel injection system control module (18).
- Brake pedal operation - from the stop (brake) light switch (19).
- Fully depressed Accelerator Pedal (AP) - from the kickdown switch (20) on the throttle cable.
- Transmission oil temperature - from a temperature sensor (6) in the transmission.

All of this information is processed by the TCM (21), which calculates which gear will provide the best driving performance based on the selected driving mode. The TCM orders gear-shifts by sending shift signals to two shift solenoid valves (S1, S2) in the transmission. Depending on the input signals, the control module decider if and when torque converter lock-up, which is engaged with the help of a special solenoid (SL), should be activated.

During gear-change, the TCM modulates the transmission oil pressure via a System Pressure Solenoid valve STH, while simultaneously sending a signal to the ignition system (22) so that the engine torque is limited as gear-changing occurs.

The TCM is also connected to the Data Link Connector (DLC) (23). Faults occurring in the electronic system are recorded in the TCM memory for subsequent display as Diagnostic Trouble Codes (DTC). If a fault is serious enough to require immediate attention, the warning lamp (24) in the combined instrument panel.

In some markets where an on-board diagnostics system OBD II is a statutory requirement the TCM can also activate the Malfunction Indicator Lamp (MIL) (25). The MIL is controlled by the Engine Control Module (ECM). A transmission malfunction that affects exhaust emissions will cause a DTC to be posted and the TCM sends a request to the ECM to activate the MIL.

The gear-shift position sensor (8) provides the TCM with information about the selected gear.

The Vehicle Speed Signal (VS) is sent from the VSS (17) which received pulses from a pulse wheel, locking wheel for the shift-lock on the output shaft. Transmission speed information is sent from the transmission speed sensor (5).

Information about engine rpm and load comes from the fuel injection system control module which also provides information about the throttle opening.
If the brake pedal is depressed, the stop (brake) light switch closes and transmits a signal to the TCM.

When the accelerator pedal is fully depressed, the kickdown switch (20) closes.

The TCM uses the above signals to calculate the following:

- The control module determines the engine power output by comparing information about the throttle opening with the values for engine load and rpm. This forms the basis for calculating gear-shift engagement pressure.
- Signals from the brake light switch are used to disengage lock-up during braking in order to avoid jolts in the transmission.