The task of the controller includes a calculation of the coolant temperature. It is produced by the voltage drop on the sensor. How correct the sensor reading the coolant temperature directly affects most processes that are controlled by a controller.
Quite often problems arise because of damage to the wires that come to the sensor. There are times when there is a broken wire at the sensor connector. Such problems lead to the fact that the fan is switched on at a low temperature. From the exhaust pipe is black smoke. If a condition exists, the instrument panel warning light "CHECK ENGINE" may not illuminate. The engine in this case, it is better not to turn off, because then he may not start. To move at low speed is still possible.
Problems can arise, if the temperature sensor coolant. To test this sensor, you need to perform simple actions. For starters, disconnect the harness from the sensor. Turn on the ignition. Engaged in circuit testing. When measuring the voltage on terminal "In" to ground should be about 5 V. If the voltage is less than 4.7 V, the connection must be considered unreliable. It's possible that wire is shorted to ground or a short circuit. You also need to check the serviceability of the controller in this case.
Turn off the ignition and measure the resistance between the contact pads of the sensor A and ground. The resistance should not be less than 1 Ohm and no more. If the resistance measures more than 1 Ohm are quite possible wire breakage.
After this you need to disconnect the controller connector and check the resistance, which will be between the sensor contact pads and the contact pads of the controller 45". It should be less than 1 Ohm. If it is greater, then the connection in the stocks unreliable.
Then measure the resistance between ground and contact pads of the sensor. It should not be less than 1 Ohm. If less, then there is a short to ground.
Do a sensor test. Measure the resistance at two values of temperature of cooling liquid. This should be done at cold and hot engine. Resistance must not vary. If there are differences, it is necessary to replace the sensor. If the sensor and circuit are in good condition, then the model checker.