Electronic Transmission and Scan Tool

Abbreviations which are commonly used for this subject description:

PCM = Powertrain Control Module
TCC = Torque Converter Clutch
TPS =Throttle Position Sensor
ECT = Engine Coolant Temperature Sensor
VSS = Vehicle Speed Sensor
PSA = (Transmission Fluid) Pressure Switch Assembly
TTS = Transmission Temperature Sensor

Vehicle: Toyota Caldina, 1998Y, 1.8 L

The solenoids S1 and S2 control forward clutch and direct clutch relatively, but the S3 solenoid controls the lock-up clutch of the torque converter. As it is signed on the diagram all these solenoids are controlled by PWM signal. Pressure in the line is altered according to the TPS position, engine coolant temperature, RPMs. This sort of adjustment provides fast shift without clutch slipping while accelerating sharply and soft gear shift while accelerating gently or cruising. To avoid irritating situations of gear changing up-shift and down-shift the overdrive button is used. Once O/D is off only first three gears are in use. This provides higher torque in the speed frame 50 to 60 km/h eliminating unnecessary up-shift.

 From comparison between the photos when O/D is "on" and "off" we can conclude that lock-up solenoid comes to action much earlier when all four gears are in use, 1850 RPMs compared to 2250 RPMs. This is the way to gain in terms of economical efficiency.
This table below is shift chart for Toyota Caldina Gear Box which is built on the basis of scan tool reading above. Video clips were trimmed to make it easier to see how solenoids come to action.

Case number 1: Code DTC 14 (ECT signal voltage is low)

This code appears if ECT sensor voltage is lower than 0.3 V what indicates that engine coolant temperature is above 140 C for one second. Also this code appears if ECT sensor is shorted to ground.

Diagnosis:

Make sure what is the real engine coolant temperature. If the temperature is normal check the connection of the sensor and harness state. Use voltage drop for this procedure. “Temperature to resistance” test of the sensor will help to eliminate miscalled sensor. Only if the sensor is ok and there is no shorted harness the ECU can be suspected as faulty.

Case number 2: Code DTC 21( TPS signal voltage high)

If voltage from TPS is higher than 4.92 V the DTC 21 will appear. Problems with sensor ground can cause this code appearance. To eliminate wiring and the ECU disconnect the TPS from supply voltage, the sensor signal should go low.

Diagnosis:

While the throttle is closed check the voltage out. It should be within 0.25 to 1.25 V. Then disconnect harness and read re-check voltage out which should be below 0.2 V. Use voltage drop test for checking ground. Also check the harness for proper connection. If all this aspects show that there is no faulty devices then only the ECU can be suspected as faulty.