TCM
TCM receives information from various input devices and uses this information to control solenoids on transmission valve body for transmission shifting and torque converter lock-up.
TCM contains a self-diagnostic system, which will store Diagnostic Trouble Codes (DTC) if failure or problem exists in electronic control system. DTC can be retrieved to determine problem area. See SELF-DIAGNOSTIC SYSTEM . TCM is located under left side of instrument panel, left of steering column near relay block.
Brakelight Switch
Brakelight switch delivers input signal to TCM, indicating vehicle braking. Brakelight switch is located on pedal support.
Output Shaft Speed Sensor
Transmission speed is input to TCM by output shaft speed sensor. Sensor is located on side of transmission.
Throttle Position (TP) Sensor
TP sensor delivers an input signal to TCM indicating throttle position. TP sensor is located on side of throttle body.
Transmission Range (TR) Switch
Transmission range switch delivers an input signal to TCM indicating shift lever position. Switch is located on side of transmission.
Vehicle Speed Sensor (VSS)
Vehicle speed signal is delivered to TCM by vehicle speed sensor. Speed sensor is driven by output shaft of transfer case and indicates actual vehicle speed.
Shift Solenoids "A" & "B"
The TCM controls transmission shifting by delivering an output signal to operate proper solenoid. See SOLENOID OPERATION table. Solenoids are located on transmission valve body.
| Shift Lever Position | Solenoid "A" | Solenoid "B" | |
|---|---|---|---|
| "D" (Drive) | |||
| 1st Gear | On | Off | |
| 2nd Gear | On | On | |
| 3rd Gear | Off | On | |
| 4th Gear | Off | Off | |
| "2" (Second) | |||
| 1st Gear | On | Off | |
| 2nd Gear | On | On | |
| "L" (Low) | |||
| 1st Gear | On | Off | |
| "R" (Reverse) | On | Off | |
| "N" Or "P" (Neutral Or Park) | On | Off | |
SOLENOID OPERATION
TCC Control Solenoid
The TCM controls torque converter lock-up by delivering an output signal to TCC solenoid. Lock-up solenoid is activated when shift lever is in "D", engine is normal operating temperature and vehicle is at specified speed. TCC solenoid is located on transmission valve body.
Condition
No signal is received from range switch or more than 2 signals are received at one time. Possible causes for either condition are
- Transmission range switch malfunction.
- Damaged wiring or connectors between transmission range switch and TCM.
- TCM malfunction.
Input/Turbine speed sensor signal is not input to TCM when vehicle is moving. Possible causes for condition are
- Input/Turbine speed sensor malfunction.
- Damaged wiring or connectors between turbine speed sensor and TCM.
- TCM malfunction.
Output speed sensor signal is not input to TCM when vehicle is moving. Possible causes for condition are
- Output speed sensor malfunction.
- Damaged wiring or connectors between turbine speed sensor and TCM.
- TCM malfunction.
Engine speed input signal is not input to TCM. Possible causes are
- Damaged wiring or connectors between ECM and TCM.
- ECM malfunction.
- TCM malfunction.
TCM outputs TCC signal, but no TCC lockup is obtained. Possible causes are
- Low ATF level.
- Torque converter slippage.
- Lock-up solenoid valve malfunction.
- TCM malfunction.
- Low line pressure.
- Control valve stuck.
Possible Causes
- Short or open circuit between TCM and solenoid.
- TCM malfunction.
- Lock-up solenoid malfunction.
- Short or open circuit between TCM and solenoid.
- TCM malfunction.
- Shift solenoid "A" malfunction.
- Short or open circuit between TCM and solenoid.
- TCM malfunction.
- Shift solenoid "B" malfunction.
TP sensor voltage is less than .1 volt or more than 5 volts. Possible causes are
- Circuit fault between TP sensor and ECM.
- Circuit fault between TP sensor and TCM.
- TP sensor malfunction.
SHIFT & TCC SOLENOIDS
- Ensure ignition is off. Disconnect TCM harness connector. Measure resistance between ground and specified solenoid terminal at TCM harness connector. See «PIN VOLTAGE CHARTS»(ref-10057-S39296041992000110700000) . Resistance should be 11-15 ohms at 68°F (20°C).
- If resistance is not as specified disconnect transmission solenoid connector and check harness between TCM and transmission connector for short or open. See «WIRING DIAGRAMS»(ref-10057-S23412969472000110700000) . If harness is okay, go to next step.
- Disconnect 3-pin transmission solenoid connector from vehicle harness. Note that solenoids ground through transmission case. Check resistance between 3-pin connector terminals and ground. Replace solenoids as necessary.
- If resistance is okay, ensure transmission case is grounded and intermittently connect battery voltage to terminals of 3-pin connector. An audible click should be heard from specified solenoid when voltage is applied.
TRANSMISSION RANGE SWITCH
Verify that starter operates with shift lever in "P" or "N" position. Turn ignition switch to ON position. Move shift lever to "R" position and verify back-up light illuminates. If either operation fails as specified, inspect switch terminal continuity. (Scheme 74)
Scheme 74
PIN VOLTAGE CHARTS
Turn ignition switch to ON position. Access TCM. DO NOT disconnect harness connector. Using DVOM, measure voltage. After verifying that appropriate condition has been met, check voltage. If voltage is not within specification, replace TCM. (Scheme 75)and (Scheme 76).
