TOYOTA PREVIA 91-97 REPAIR MANUAL

2-16 ENGINE ELECTRICAL

SENDING UNITS AND SENSORS

General Information

»See Figure 53

—This section describes the operating principles of sending

warning lights and gauges. Sensors which provide informati

mits,

n to

the Electronic Control Module (ECM) are covered in Section' of this

manual.

Instrument panels contain a number of indicating devices (gaug^p and

warning lights). These devices are composed of two separate comp

One is the sending unit, mounted on the engine or other remote pai

vehicle, and the other is the actual gauge or light in the instrument

Several types of sending units exist, however most can be charai

ments.

of the

iterized

as being either a pressure type or a resistance type. Pressure type sending

units convert liquid pressure into an electrical signal which is sent :D the

gauge. Resistance type sending units are most often used to measmfe tem-

perature and use variable resistance to control the current flow bade to the

indicating device. Both types of sending units are connected in serls by a

wire to the battery (through the ignition switch). When the ignition $ turned

ON, current flows from the battery through the indicating device an|:| on to

the sending unit.

Engine Coolant Temperature Gauge

Oil Pressure Switch

Fig. 53 Engine coolant and oil switch locations

Coolant Temperature Sensor

TESTING

I See Figures 54 and 55

Using an ohmmeter, measure the resistance between the termina

to the chart, if the resistance is not as specified, replace the sensor.

REMOVAL & INSTALLATION

5. Refer


6. Turn the ignition key to the OFF position. Disconnect the negative
   battery cable.


7. Locate the coolant temperature sending unit on the engine,


8. Disconnect the sending unit electrical harness.


9. Drain the engine coolant below the level of the switch.


10. Unfasten and remove the sending unit from the engine. Discard the
    old gasket if equipped.

Engine coolant temperature °C (°F)

50(122)

1 20 (248)

Resistance (Q)

Approx. 200

Approx. 19.4

Fig. 54 Coolant temperature sensor specifications

Fig. 55 Inspecting the coolant temperature sensor for resistance

To install:

6. Coat the new sending unit with Teflon® tape or electrically conduc-
   tive sealer. Place a new gasket on the sender.


7. Install the sending unit and tighten to 18 ft. Ibs. (24 Nm).


8. Attach the sending unit's electrical connector.


9. Fill the engine with coolant.


10. Start the engine, allow it to reach operating temperature and check
    for leaks.


11. Check for proper sending unit operation.

Oil Pressure Sensor

TESTING

A quick way to determine if the gauge (idiot light) or sending unit is

faulty is to disconnect the sending unit electrical harness and ground it (

two terminal, jumper between the terminals). If the gauge responds, the

sending unit may be faulty. Proceed with the sending unit test.