Inspection of the Coolant Temperature Gauge Sensor

The sensor is located on the coolant pipe at the rear of the water pump (4A-FE engine) or on the left side of the cylinder head (3S-FE engine). The sensor is supplied with voltage from the instrument panel (through the ignition switch and fuse). It contains a thermistor, an electronic element whose electrical resistance decreases as temperature rises. At low coolant temperature, the sensor has high resistance and low current flows through it. The gauge needle on the instrument panel is in the "cold" part of the scale. As temperature rises, the sensor resistance decreases, the current increases and the needle moves toward the upper part of the scale. If the sensor is faulty, replace it.

· If the gauge appears to be faulty, first check the other gauges; if they also do not work or give incorrect readings, check the instrument panel power supply circuit. If only the gauge itself is faulty, check it as follows.

· If the gauge needle remains in the low-temperature part of the scale with the engine warm, disconnect the sensor connector and ground the wire to the cylinder head. If the needle now deflects to the right when the ignition is switched on, the sensor is faulty and must be replaced. If the needle does not move, remove the instrument panel and check the wires connecting the sensor to the gauge. If the wiring is good and the gauge does not respond, the gauge is faulty and must be replaced. · If the gauge needle indicates high temperature with a cold engine, disconnect the sensor wire. If the needle now returns to the left when the ignition is switched on, the sensor is faulty and must be replaced. If the needle remains in the right part of the scale, check the wiring as described above.