Transmission Control Module
A microcomputer controls the transmission by receiving and processing signals from various switches and sensors. The microcomputer determines shift sequences, shift timing, and clutch apply and release characteristics. The microcomputer is an independent controller and is referred to as a transmission control module (TCM). The pressure switch manifold (PSM) and the internal mode switch (IMS) provide operator input to the TCM. Other data sent to the TCM include throttle position, engine, turbine, and output speeds, and sump temperature. Any active special function, such as anti-lock brakes or power take-off, is also an input to the TCM. The TCM processes this data to determine proper shift points, to monitor the current range, to perform ratio tests, and to compile diagnostic data. The TCM is programmed to protect the transmission and other vehicle driveline components by inhibiting actions, such as full-throttle NEUTRAL-to-range shifts and high speed direction changes. The TCM determines if a system malfunction exists and stores diagnostic codes related to the malfunction. The codes, accessed by the service technician, are used in diagnosing persistent or intermittent trouble in the system.
Throttle Position/Torque Management
The TCM receives input on throttle position/torque management from a signal transmitted by the engine control module (ECM).
The ECM communicates directly to the transmission electronic controls over an SAE J1850 or J1939 serial communication interface (SCI) data link. The TCM must be calibrated to receive these signals.
Speed Sensors
Important: Do not rotate the sensor in the retaining bracket. Changing the sensor/bracket orientation may cause improper operation.
There are 3 speed sensors typically required for use with 1000 Series transmissions. They include the engine speed sensor, the turbine speed sensor, and the output speed sensor. The speed sensors provide revolutions per minute (RPM) information to the TCM. The speed ratios between the various sensors allow the TCM to determine the transmission operating range. Speed sensor information is also used to control the timing of clutch apply pressures, resulting in the best possible shift quality. Hydraulic conditions are detected by comparing the speed sensor information for the current range, to the range of the speed sensor information stored in TCM memory. The speed sensors are variable reluctance devices that convert mechanical motion to an AC voltage. Each sensor consists of a wire coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing that is mounted adjacent to a rotating ferrous member.
Shift Selector
The vehicle is equipped with a column type shift selector. In addition to the column shifter, another component associated with the shift selector is the internal mode switch (IMS), which is mounted internally on the selector shaft. The IMS transmits selector position information to the TCM. The IMS detects the angular position of the shift selector shaft. This position is communicated to the TCM so that certain vehicle control functions can be coordinated with the position of the shift controls. The IMS has redundant circuitry to alert the TCM in the event of a single wire or switch failure. The neutral signal output of the IMS is typically used as confirmation that the transmission is in NEUTRAL before the engine starter is engaged. The IMS is interfaced to the starter circuit.
The operator chooses the transmission range by moving the selector lever to the appropriate gate position. When properly adjusted, the shifter gates prevent inadvertent shifting between ranges, and corresponds to the internal transmission detent positions. A positive detent is provided in the transmission in order to maintain the selector shaft in the selected position.
The TCM shift calibration determines the available forward ranges for each selector position. Although specific installations vary, typical selector positions for the 1000 Series include the following:
P - PARK: The parking pawl is engaged. The transmission is in NEUTRAL.R - REVERSE: REVERSE is selected in order to move the vehicle backward.
N - NEUTRAL: NEUTRAL may be used when starting the engine and for stationary operations. The TCM disables the starter switch if a range other than NEUTRAL or PARK is selected before starting the vehicle.
D - DRIVE: DRIVE is the highest forward range used for normal driving. The transmission shifts to first range for starting, then automatically upshifts through the ranges, as operating conditions permit, until the highest range is attained.
M - Manual: Manual selection of ranges is provided by moving the selector to the M - MANUAL position. A driver shift request switch has been added to the column shift lever. The driver information center (DIC) then shows the 6 available ranges with the current range bracketed. The bracketed range is the highest attainable range with all gears below accessible, for example, when 4th range is selected, ranges 1st through 4th are available. By using the +/- buttons on the gear select lever, the driver can select the range of gears desired for their current driving conditions.
1 - Manual LOW: Manual LOW provides first gear operation only.
Internal Components
Several components of the 1000 Series electrical control system are located within the transmission as part of the main control valve body. These components include 3 types of solenoids for controlling the hydraulic action of the valves. They include the PSM and an internal wiring harness that links the internal components with the TCM.
Solenoids
The 1000 Series control valve body contains both normally closed (N/C) and normally open (N/O) solenoids. A N/C solenoid remains closed until a signal from the TCM energizes the solenoid. A N/O solenoid remains open until the TCM energizes the solenoid. When a solenoid valve is in the closed position, the valve blocks the flow. When a solenoid valve is in the open position, flow is permitted through the valve. Shift solenoid 1 (SS1) (4), shift solenoid 2 (SS2) (2) and shift solenoid 3 (SS3) (3) are N/C. Both solenoid types have an orifice, electrical windings, an iron core, and a steel check ball.
Shift solenoids provide the necessary logic to distribute fluid to the correct clutches. The shift solenoids provide either full control main pressure or exhaust to the head of each of the corresponding shift valves. Since the valve states, stroked or unstroked, are critical to providing the correct transmission range, each shift valve has a pressure switch, located in the PSM, which provides feedback to the computer regarding the position of the valve.
Modulated main pressure solenoid (7) is a N/C solenoid used to modulate the transmission main pressure. Under specific conditions, such as low throttle setting, low engine torque, low engine speed, and low transmission output speeds, the TCM commands the solenoid ON. When the solenoid is applied, fluid is routed to the main pressure regulator valve; this in turn reduces the main pressure schedule and improves the volume of oil through the overage circuit. By modulating main pressure, the cooler flow at idle can be increased, allowing improved cooling and reducing transmission pump noise.
Pressure control solenoid 1 (PCS1) (6), pressure control solenoid 2 (PCS2) (4), and the torque converter clutch (TCC) (1) are used to control on-coming, off-going, and holding pressure to the 5 clutches and the TCC. These solenoids are referred to as variable bleed solenoids, since the output hydraulic pressure supplied by these solenoids is proportional to the controlled current command.
Pressure Switch Manifold
The PSM is a multiple-switch assembly made up of 3 N/O pressure switches, PS1 (4), PS2 (3), and PS3 (2) and 1 N/C pressure switch. N/O pressure switches, PS1, PS2, and PS3, correspond to shift valves SS1, SS2, and SS3. Fluid pressures are fed from shift valves SS1, SS2, and SS3 to the manual selector valve and to the pressure switches based on the positions of the valves and shift selector. The shift valve fluid pressures reflect the logic condition at the corresponding solenoids. This logic indicates the current transmission operating range to the TCM.
The 3 fluid pressure switches corresponding to the shift valves are N/O, contacts not touching, when no fluid pressure is present, so that electrical current is stopped at the switch. When fluid pressure is routed to the switch, it moves the diaphragm and upper contact so that the contact element touches both the positive and ground contacts. This closes the circuit and allows current to flow from the positive contact and through the switch.
Pressure switch 4 (PS4) (1) corresponding to REVERSE is N/C, since fluid pressure is always present unless the selector valve is moved to REVERSE. The PSM also contains a transmission fluid temperature (TFT) sensor thermistor (5) for sump temperature. Changes in sump fluid temperature are indicated by changes in sensor resistance. Increasing temperature causes decreased sensor resistance. The resistance value is then relayed to the TCM as an input for shift control.
Internal Wiring Harness
The internal wiring harness has connectors for shift solenoids SS1 (7), SS2 (3) and SS3 (4), PCS1 (6) and PCS2 (5), TCC pressure control solenoid (TCC PCS) (2), and the PSM (1). There is also a connector for the modulated main (MOD MAIN) pressure solenoid (9) and the IMS (10). All of these connectors go to the main electrical connector (8). The transmission main electrical connector transports signals from these connectors to the TCM via the external harness.
