When driving, the driver monitors not only the situation on the road, but also the condition of the car. The presence of charging and oil pressure, speed, engine speed. The most important thing is the amount of fuel in the tank. But there is some inconvenience when the pointer readings fluctuate greatly.
The sensor and indicator allow to track the fuel level in the tank. Moreover, the sensor on all models of VAZ cars is used of a float type. The difference can only be observed in the design. For example, on vehicles with an injection system, the level sensors and the fuel pump are combined into one functional unit. A rheostat is used as an active element of the level sensor. To carry out repairs, you need to know the principle of its operation and the connection of the main units.
Design and principle of operation
The sensing element of the sensor is a rheostat (variable resistor). The sensor output is two control wires, ground is connected separately. The level sensor is based on a lever. On one end, a small plastic float is installed on it, but the other end is connected to a rheostat, or more precisely, to its slider connected to the mass.
The rheostat has two outputs, one of which (the lower one) is not connected to anything, and the upper one gives an analog signal that goes to the fuel level indicator. The voltage is measured in the monitoring system. The indicator is a voltmeter, its full scale is equal to the value of the supply voltage. In simple terms, the indicator measures the voltage, and the level sensor changes its value depending on the amount of fuel in the tank.
The slider is also responsible for turning on the warning lamp. When there are five liters of gasoline in the tank, a light on the indicator lights up. This is realized by the fact that the second contact coming from the sensor body is connected to the control lamp. The positive terminal is connected to this lamp, and the negative one goes to the sensor.
Repair and diagnostics of the level sensor
First you need to see what symptoms are observed. The arrow of the device can be kept at a maximum, at a minimum, or even float along the scale. The indicator lamp is either constantly on, or never lights up, and may even blink at all. Sometimes symptoms of lamp and device malfunction may appear at the same time. But the breakdown is in the sensor.
Unscrew the fastening nuts after removing the two hoses from the pipes. Remove the sensor and assess its condition by its appearance. If the float is broken and there is gasoline in it, then it is better to replace it. You can, of course, use a soldering iron to warm up the breakdown site. But don't use sealants or epoxy. Gasoline will eat away at these materials.
Now check the condition of the rheostat and the slider. It is possible that the slider has moved away from the surface of the resistor and therefore the arrow will be constantly at zero. If the arrow is constantly at the maximum, then there is a short circuit in the rheostat, it has lost its resistance. In this case, only its replacement is required.
But if the position of the arrow is unstable, constantly changing, then the slider does not fit tightly to the surface. Try to move it to the edge of the track, there is less rheostat production. To be sure, take an ohmmeter and check the impedance of the resistor. If it is very different from 345 ohms, then the best repair is to replace the level sensor.
