Table of contents: Checking lamp switches and electric… ↓ Checking the sensor switches ↓
Most of the on-board electrical consumers are switched on and off manually using a switch. In addition, there are automatic switches (sensors). These include, for example, the oil pressure sensor and the brake fluid level sensor.
The switch mainly serves to close and open an electrical circuit. There are switches that open the connection to the "ground" (-), and switches that break the connection to the positive potential (+).
Checking lamp switches and electric motors
1. Remove the appropriate switch. Simple switches have only two terminals for connecting the wire. In this case, one terminal should always have (+), and the other terminal has a plus after switching on. There are also switches with several terminals. For these switches, you should find out from the diagram to which terminal the voltage should be supplied. Turn on the ignition first, if necessary.
2. Check the voltage with a test lamp. If the test lamp lights up, turn on the switch and check the voltage at its output terminal. If there is voltage, then we can say with certainty that the switch is working. If there is no voltage at the input terminal, this indicates a break in the supply wire. You need to check the power supply according to the electrical diagram, and if necessary, lay a new wire.
Checking the sensor switches
Sensor switches are, for example, sensors for the brake fluid level indicator lights, engine oil and coolant.
3 Connect the "ringing" device to the two terminals of the sensor (test light or ohmmeter). To do this, disconnect the wires from the sensor.
Attention/ Sensors screwed into the cylinder block, as a rule, do not have a "ground" (-) wire, since their connection to the "ground" (-) occurs through the cylinder block, to which the body of the sensor itself is connected.
When closed (included) the sensor the device should show the passage of current. For such a "ringing" it is best to use an ohmmeter: when the sensor is closed it should show 0 Ohm, and when open - ∞ Ohm (infinite resistance).
The fastest way to check the functionality of switches such as the coolant or brake fluid level indicator light sensor is to disconnect the power supply wire from it with the ignition on, which is then connected to a "solid" "ground" (-), for example, to the cylinder block. If the light on the instrument panel now lights up, then the sensor is faulty.
A special case is the oil pressure sensor. When the engine is stopped, its contact is closed and when the ignition is on, the engine oil pressure indicator light is on. And only when the engine is running, when a certain oil pressure is reached, the switch opens.