Windshield washer tank and fluid level sensor

In most cars, the windshield washer fluid tank is located in the engine bay or around the front wheel wells, often behind the front bumper or one of the front fenders. The washer fluid pump/motor and the washer fluid level sensor are attached to the windshield washer fluid tank.
This photo shows the windshield washer fluid tank with the front bumper removed.

How the windshield washer fluid level sensor works

A typical washer fluid level sensor is a magnetically operated switch called "reed switch." It's mounted at the bottom of the windshield washer fluid tank. The sensor consists of a cylinder casing with a magnetic float inside. The reed switch is built into the base of the sensor.

When the washer fluid level drops beyond the minimum mark, the float sinks to the bottom of the cylinder and the magnet activates the reed switch. The reed switch closes the circuit and the "Low washer fluid level" warning light comes on. In some cars, the sensor works in reverse: it opens when the fluid level drops.

Windshield washer fluid tank/sensor problems:

One of the common problems is when the washer fluid sensor stops working. This may cause the "Low washer fluid" warning light to come on even when the tank is full or not to come on when the tank is empty. This could be caused by the float being stuck inside the cylinder or a problem with the connector or wiring. If the float is stuck inside the cylinder, tapping lightly on the washer fluid tank can help free it.

If the washer fluid sensor has failed, it will have to be replaced. In some cars, it's fairly easy: the sensor is held by a rubber grommet at the bottom of the washer fluid tank. In other cars, the washer fluid sensor might need to be replaced together with the washer fluid tank as one unit.

Another common problem is when the windshield washer fluid tank breaks or cracks. This might happen if the tank is damaged due to an impact or if the fluid/water freezes inside the tank. The symptom of a cracked washer fluid tank is when the fluid leaks out. If the washer fluid tank is confirmed to be damaged/cracked, it will need to be replaced. Depending on the location the repair shop may charge 1-2 hours of labor plus the part, which is not very expensive.

How the windshield washer fluid level sensor is tested

Testing the washer fluid level sensor is easy. To show you, we got a good working fluid level sensor.

First we measure its resistance when it's in the proper position and the float is at the bottom of the cylinder casing. The sensor's resistance is at 0 ohms which means it's closed when the washer fluid level is low.

When we flip the sensor upside down, the float with magnet slides away from the reed switch and the multimeter shows OL (open loop), which means the circuit is open. The sensor is working properly.