TOYOTA PREVIA 91-97 REPAIR MANUAL

DRIVEABILITY AND EMISSIONS CONTROLS 4-23

Fig. 66 Test both terminals of the coolant temperature sensor

using an ohmmeter

3. With the engine cold and the ignition switch in the OFF position, -
   measure and note the ETC sensor resistance.


4. Connect the engine wiring harness to the sensor.


5. Start the engine and allow the engine to reach normal operating tem-
   perature.


6. Once the engine has reached normal operating temperature, turn the
   engine OFF.


7. Once again, disconnect the engine wiring harness from the ETC sen-
   sor.


8. Measure and note the ETC sensor resistance with the engine hot.


9. Compare the cold and hot ETC sensor resistance measurements with
   the accompanying chart.


10. If readings do not approximate those in the chart, the sensor may be
    faulty.

REMOVAL & INSTALLATION

» See Figure 67

1. Drain the engine coolant.


2. Remove the RH seat and engine service hole cover.


3. Disconnect the ETC sensor wiring.


4. Remove the sensor and gasket.

Fig. 67 Remove the wiring from the coolant temperature sensor,

then unthread it

To install:

5. Install the new sensor with gasket. Tighten the sensor to 17 ft. Ibs.
   (25 Nm).


6. Connect the wiring to the sensor.


7. Reinstall RH seat and engine service hole cover.


8. Refill the engine with coolant and water mixture.

Intake Air Temperature (IAT) Sensor

OPERATION

The Intake Air Temperature sensor is built into the mass air flow meter

and senses the intake air temperature. A thermistor built into the sensor

changes the resistance value according to the intake air temperature. The

lower the intake air temperature, the greater the thermistor resistance value,

and the higher the intake air temperature, the lower the thermistor resistance

value. The intake air temperature is connected to the ECM. If the IAT sensor

is faulty it cannot be replaced separately. The MAP meter must be replaced

as an assembly. Refer to the air flow meter procedures.

Volume Airflow Meter

OPERATION

The 2TZ-FE engine utilizes a Volume Air Flow Meter (VAF) contains a

spring-loaded measuring plate. The plate is connected to a potentiometer which

controls the signal to the ECM. In this way, the control unit is advised of intake

air volume and can control injector duration and ignition advance accordingly.

TESTING

» See Figures 68, 69, 70 and 71

1. To test the VAF meter on the vehicle, disconnect the meter wiring.
   a. Using an ohmmeter, measure the resistance between each terminal.
   b. If the resistance is not within specifications, replace the VAF
   meter.
   c. Reconnect the harness to the VAF meter.


2. Testing the meter off the vehicle perform the following:
   a. Using an ohmmeter, measure the resistance between each terminal
   by moving the measuring plate.
   b. The resistance between terminals E2 and VS will change in a wave
   pattern as the measuring plate slowly opens.
   c. If the resistance is not as specified, replace the VAF meter.

FC E1 VC E2 VS THA

Ohmmeter

T

Fig. 68 Use the ohmmeter to test between each of the terminals

on the VAF meter—2TZ-FE engine