ELECTRONIC CONTROL MODULE
ECM receives information from various input devices and uses this information to control shift solenoids and torque converter lock-up. ECM contains a self-diagnostic system, which will store a Diagnostic Trouble Code (DTC) if failure or problem exists in the electronic control system.
DTC can be retrieved to determine transaxle problem area. See DIAGNOSIS & TESTING . ECM is located behind glove compartment.
Park/Neutral Position Switch
PNP switch delivers an input signal to ECM to indicate selector lever position. PNP switch is located on side of transaxle, below solenoid connector.
Throttle Position Sensor
TP sensor delivers an input signal to ECM indicating throttle position. TP sensor is located on side of throttle body.
Vehicle Speed Sensor
Vehicle speed signal is delivered to ABS ECU by ABS wheel speed sensors. ABS ECU converts signals into a 4-pulse signal and outputs signal to instrument cluster. Instrument cluster converts signal to a more precise waveform and outputs signal to ECM. Speed sensors are located at each wheel.
Brakelight Switch
Brakelight switch delivers input signal to ECM, indicating vehicle braking. Brakelight switch is located on brake pedal support.
Overdrive Switch
OD switch provides an input signal to ECM to indicate when overdrive is selected by vehicle operator. When OD switch is depressed to ON position, transaxle will shift into 4th gear when selector lever is in "D" position, and OD OFF light on instrument panel will go off. When OD switch is released to OFF position, transaxle will shift into 3rd gear, and OD OFF light will illuminate. OD switch is mounted on selector lever.
Engine Coolant Temperature Sensor
Engine coolant temperature sensor delivers input signal to ECM, indicating engine coolant temperature. ECT sensor is located at right rear corner of engine, near upper radiator hose.
Cruise Control Electronic Control Unit
Cruise control ECU delivers an input signal to control overdrive operation in accordance with vehicle speed when cruise control is operating. When in overdrive with cruise control on, if vehicle speed drops 3 MPH less than set speed, overdrive is released to prevent reduction in vehicle speed. Once vehicle speed is more than set speed, overdrive is resumed. Cruise control ECU is located behind instrument panel on driver's side of vehicle.
Input Turbine Speed Sensor
Input turbine speed sensor detects rotation of input shaft. By comparing input turbine speed sensor signal and counter gear speed sensor signal, ECM detects shift timing of gears and controls engine torque and hydraulic pressure in response to various conditions, resulting in smooth transaxle shifting. see scheme 1
Counter Gear Speed Sensor
Counter gear speed sensor detects rotation of counter drive gear. By comparing counter gear speed sensor signal and input turbine speed sensor signal, ECM detects shift timing of gears and controls engine torque and hydraulic pressure in response to various conditions, resulting in smooth transaxle shifting. see scheme 1
Shift Solenoids SL1, SL2 & S4
ECM controls transaxle shifting by delivering an output signal to operate proper shift solenoid. Solenoids are located on transaxle valve body. (Scheme 93) Solenoids are operated in accordance with selector lever position. If a solenoid malfunctions, ECM defaults transaxle to a designated gear. (Scheme 94)
Note. ECM provides a fail-safe system which places transaxle in a designated gear depending on which solenoid fails. In some gears, fail-safe system will not be activated and transaxle will shift to the failsafe gear. (Scheme 94)
Shift Solenoid DSL
ECM uses signals from TP sensor, airflow meter and crankshaft position sensor to monitor torque converter lock-up engagement condition. ECM compares torque converter lock-up engagement condition with lock-up schedule in ECM memory to detect a malfunction with valve body, torque converter clutch or shift solenoid DSL. Shift solenoid DSL controls hydraulic pressure acting on lock-up relay valve, which contains torque converter clutch lock-up. Shift solenoid DSL is located on transaxle valve body. (Scheme 93)
Shift Solenoid SLT
ECM controls line pressure by sending a predetermined duty ratio to shift solenoid SLT, modulating line pressure and generating throttle pressure. Shift solenoid SLT is used to precisely and minutely modulate and generate line pressure according to accelerator pedal effort, or engine power output detected. Shift solenoid SLT is located on transaxle valve body. (Scheme 93)
Scheme 93
Scheme 94
Disconnect electrical connector from brakelight switch located near brake pedal. Using ohmmeter, ensure continuity exists between switch terminals No. 1 and 2 with brake pedal depressed. (Scheme 95) Continuity should exist between terminals No. 3 and 4 with pedal released. Replace switch if continuity is not as specified.
Scheme 95
Note. RX300 uses a 6-pin Overdrive switch connector.
Disconnect electrical connector from Overdrive (OD) switch located on selector lever. Using a DVOM, ensure continuity exists between terminals No. 2 and 4 on ES300 (terminals No. 1 and 3 on RX300 at same connector terminal locations) with switch depressed (ON) position. (Scheme 96) Ensure no continuity exists with switch released (OFF) position. Replace switch if defective.
Scheme 96
Disconnect harness connector at PNP switch. Switch is located on side of transaxle. Using ohmmeter, check for continuity between specified terminals in accordance with selector lever position. (Scheme 97) Replace PNP switch if continuity is not as specified. If switch is okay, check and repair wiring harness or connector between PNP switch and ECM.
Scheme 97
Note. The following information can also be used to diagnose DTC P0770. For testing of shift solenoid SLT, see DTC P1760: SHIFT SOLENOID SLT under DIAGNOSTIC TESTS.
Scheme 98
- Raise and support vehicle. Remove transaxle oil pan. Remove shift solenoid DSL. (Scheme 93) Connect battery voltage to solenoid. Apply 71 psi (5 kg/cm 2 ) of compressed air to solenoid with battery voltage connected. (Scheme 98)
- With battery voltage connected, air should not pass through solenoid. Disconnect voltage to solenoid. Ensure air does pass through solenoid. Replace solenoid as necessary.
Note. The following information can also be used to diagnose DTCs P0750, P0755 and P0765. For testing of shift solenoid SLT, see DTC P1760: SHIFT SOLENOID SLT under DIAGNOSTIC TESTS.
- Raise and support vehicle. Remove transaxle oil pan. Remove shift solenoid(s). (Scheme 93) Using a DVOM, measure resistance between shift solenoid SL1 and SL2 terminals. On shift solenoid S4, measure resistance between ground and solenoid terminal. On shift solenoids SL1 and SL2, resistance should be 5.1-5.5 ohms. On shift solenoid S4, resistance should be 11-15 ohms. On all solenoids, if resistance is not as specified, replace solenoid.
- To check shift solenoids SL1 and SL2 operation, connect positive lead with 23-watt bulb from battery to terminal No. 1 (White wire on shift solenoid SL1, or Yellow wire on shift solenoid SL2) of solenoid. Connect negative lead to terminal No. 2 of solenoid. With power supplied to solenoid, ensure solenoid valve moves outward. With power disconnected, ensure solenoid valve moves inward. Replace solenoid if operating sound cannot be heard. If solenoid operates, diagnose valve body malfunction.
- To check shift solenoid S4 operation, connect positive lead with 23-watt bulb from battery to solenoid terminal. Connect negative lead to solenoid body. With power supplied to solenoid, ensure solenoid valve moves outward. With power disconnected, ensure solenoid valve moves inward. Replace solenoid if operating sound cannot be heard. If solenoid operates, diagnose valve body malfunction.
PIN VOLTAGE TESTS
Access ECM located behind glove compartment. Turn ignition switch to ON position. Using a DVOM, backprobe ECM harness connector. Measure voltage between selected terminals. (Scheme 99)and (Scheme 100). Voltage should be as specified.
Scheme 99
Scheme 100
Overdrive switch is mounted on selector lever. Replacement information is not available from manufacturer.