Electronic Control Systems

To determine the exact gear shifting and lock-up engagement points, based on the selected driving mode, the Transmission Control Module (TCM) (4) is supplied with signals describing:
- 1 selected gear position, from gear-shift position sensor (5)
- 2 selected driving mode, from the mode selector (3)
- 3 road speed, from the speedometer (27).
- 4 speed of front planetary train sun wheel, from transmission speed sensor (12)
- 5 engine speed (RPM) and load, from Engine Control Module (ECM) (28)
- 6 engine speed (RPM) and load, from ECM (28)
- 7 brake pedal operation, from stop (brake) light switch (29)
- 8 fully depressed Accelerator Pedal (AP), from kickdown switch (30)
- 9 transmission oil temperature, from a temperature sensor (13) in the transmission.

The information is processed by the TCM which computes which gear will provide the best driving performance for the selected driving mode.
The control module orders gear-shifts by sending shift signals to two Shift Solenoid Valves (S1, S2) incorporated in the transmission. Depending on the signals the TCM receives the torque converter lock-up is activated. Lock-up is controlled by the Lock-up Solenoid (SL).

Unlike earlier automatic transmissions, lock-up is available in the AW 30-40 on three gears, 2nd, 3rd and 4th. When and how the function is engaged depends on factors such as the transmission oil temperature and outside temperature.

During gear shifting, the transmission line pressure is controlled indirectly by System Pressure Solenoid Valve (STH). Torque reduction takes place in the following sequence:
- a signal is sent from the AW 30-40 TCM to the ECM (28).
- the engine torque is reduced (depending on the current torque)
- the ECM sends an acknowledgement
- line pressure in the transmission is adjusted
- the transmission shifts gear.

This makes gear shifts smoother and reduces mechanical wear.
The TCM is also connected to the Data Link Connector (DLC) (6). Faults occurring in the electronic system are recorded in the control module memory for subsequent display as Diagnostic Trouble Codes (DTC). If a fault is serious enough to require immediate attention, the warning light (7) on the combined instrument panel flashes.

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) (29). The MIL is controlled by the ECM. If there is an exhaust emission-related transmission malfunction a diagnostic trouble code (DTC) will be stored and the TCM sends a request to the ECM to activate the MIL.