IDENTIFICATION
Identification plate is located on side of transmission case. (Scheme 5) Identification plate information may be required when ordering replacement components. Transmission RPO code for Catera is ML4.
Scheme 5
DESCRIPTION & OPERATION
Automatic transmission is electronically controlled, providing 4 forward speeds and Reverse. Transmission uses a gear-type oil pump to supply all hydraulic pressure needed for operation. Transmission consists of a torque converter, 4 clutch assemblies, planetary gears and brake band. (Scheme 6)
Transmission shifting and torque converter lock-up are controlled by Powertrain Control Module (PCM) or Transmission Control Module (TCM). PCM or TCM receives information from various input devices and uses this information to control shift solenoids, band apply solenoid and Torque Converter Clutch (TCC) solenoid. PCM or TCM uses input signals to control force motor solenoid (also referred to as pressure control solenoid) operation, which activates pressure regulator valve for controlling line pressure.
A torque management control system is used to reduce engagement shock caused by a change in vehicle speed during shifting. PCM/TCM contains a self-diagnostic system which stores a Diagnostic Trouble Code (DTC) if a specified failure or problem is present in transmission electronic control system. If DTC has set, transmission light on instrument panel will light. DTC may be retrieved to determine transmission problem area. For additional information on self-diagnostic system, see appropriate HYDRA-MATIC 4L30-E ELECTRONIC CONTROLS article.
Transmission is capable of 3 different shift modes. These modes are ECONOMY/NORMAL mode, SPORT/POWER mode and WINTER mode. ECONOMY/NORMAL and SPORT/POWER mode may be selected by pressing SPORT/POWER mode switch. SPORT/POWER mode indicator light will illuminate. WINTER mode may be selected by pressing button mounted on center console, near gear selector. Shift modes are used to change transmission shift points for various vehicle operating conditions.
SPORT/POWER Mode - Depressing SPORT/POWER mode switch changes transmission operating mode between ECONOMY/NORMAL and SPORT/POWER modes. In SPORT/POWER mode, TCM delays part throttle upshifts for greater acceleration. TCM also signals pressure control solenoid to increase line pressure for additional torque requirements in SPORT/POWER mode. Higher line pressure creates firmer shifts and more holding force for clutches and band.
ECONOMY/NORMAL Mode - ECONOMY/NORMAL mode provides for better fuel economy by having TCM initiate earlier part throttle upshifts. Line pressure is lower in order to provide smoother upshifts and downshifts.
WINTER Mode - In WINTER mode, TCM changes shift solenoid states in order to start transmission in 3rd gear. By starting off in 3rd gear, less torque is created, thereby reducing tire slippage on ice and snow. When WINTER mode is selected, TCM overrides all other modes. TCM only enters WINTER mode when gear selector is in "D" (Overdrive), vehicle speed is less than 6 MPH, transmission fluid temperature is less than 266°F (130°C), wide open throttle switch is off and throttle opening is less than 7 percent. WINTER mode is canceled if WINTER mode button is depressed, gear selector is moved to "P" position or a lower drive range, ignition is turned off, transmission fluid temperature is more than 266°F (130°C), or wide open throttle switch is activated. When WINTER mode is canceled due to one of these conditions, TCM returns vehicle to economy mode, regardless of operating mode before selecting WINTER mode.
Transmission is equipped with shift lock system. Shift lock system prevents gear selector from being moved from "P" position unless brake pedal is depressed, ignition is on and release button on gear selector is depressed.
