HHO Fluid Level Sensor

How the Probe Works

The 4-probe electrolyte level sensor has four metal probes. They are made of 316L stainless steel and the tip of the probe at the bottom is what gives the liquid level indication. It works by measuring the conductivity of the liquid electrolyte. When a probe tip contacts electrolyte, an electrical connection to the reference sensor (longer probe) is formed, which provides an indication of fluid level.

HHO electrolyte level sensor probe side red green white blackHHO electrolyte level sensor probe top red green white blackprobe color coded crop

probe color coded image from bottom without baffle crop


 1. Green Probe - Excess (off)  - When the tip is immersed in the electrolyte indicates that there is too much liquid in the tank. As a result, the PWM turns off automatically if excess fluid is not removed. It turns off to protect the vehicle, as the electrolyte from the tank can pass through the hose to another part of the car. This is especially true for systems without a bubbler.

 2. White Probe - Full  - When the tip is immersed in the electrolyte it indicates that the fluid level is filled and PWM functions normally.

 3. Red Probe - Low / Empty (off)  - When the tip is immersed in the electrolyte indicates the tank is not empty and PWM functions normally . If the tip of the probe is exposed (not submerged in the liquid), the system will automatically shut down and will not restart until fluid is detected. HHO cells tend to burn without a sufficient amount of liquid flowing through them.

 4. Black Probe - Reference  - The longest probe is the reference probe. Without it, the other 3 probes have no benchmark to measure against. The other three probes measure the liquid level in the tank (reservoir).

NOTE: When we mention colors, here, we are talking about the colors in the drawings of the probe. The actual fluid sensor is not colored. It is stainless steel, Silver in appearance.


The LCD in car display gives a visual indication as to how much fluid is in the Electrolyte Tank

You can see on the right of the display the 2 bars indicating correct electrolyte level:


  • 3 Bar  - Indicates excessive electrolyte and the HHO generator is turned off to prevent overflow.
  • 2 Bar -  Indicates correct electrolyte level.
  • 1 Bar  - Indicates not enough electrolyte in the tank and needs to be refilled.
  • No Bar  - System will shut down to protect because it is not enough electrolyte for circulation.


This indication is also given by the LED lights on the front of the PWM

pwm and display 280x209

 Starting from left the Four LEDs Indicate:

  1. PWM System ON - Indicated by Green LED
  2. Excess Electrolyte Level - Indicated by Blue LED
  3. Full Electrolyte Level - Indicated by Blue LED
  4. Low Electrolyte Level - Indicated by Blue LED


Changing the Probe Liquid Level

Now that you know how the probe works, you can cut the probe lengths to suit your tank.

Some Considerations:

The probe will only work in plastic tanks. It has not been tested in metal tanks.

Some types of adhesive cannot be used to log the probe to the tank. If the adhesive is CONDUCTIVE please do not use it. Resistance between electrodes is measured to determine the level of electrolytes, so conductive adhesive will distort the measurements and therefore not going to work

You do not necessarily need the plastic deflector for the probe works. However, the probe without the deflector works best if there is foam in the tank due to too much agitation or oil contamination. A drop of oil is enough to contaminate the electrolyte and cause foaming. The deflector will measure the height of the foam and give a wrong indication. The foam height is the height of the fluid. The foam in the tank is never a good signal.


How to cut the lengths of the probe to modify for your tank

  1. You will need a good wire cutter or a small handheld grinder to cut to length. The probes are quite hard.
  2. You will need to remove the plastic baffle. You can slide it off with a little effort or cut it off with a dremel. The dremel is preferred.
  3. The Black Probe - has to be at the bottom of the tank, but without touching the bottom. A few millimeters to a centimeter from the bottom is sufficient.
  4. The Red Probe - should be almost as long as the reference probe. A few millimeters to a centimeter shorter than the black is fine.
  5. The White Probe - should be at the height of your tank you have in mind the level of electrolyte complete.
  6. TheGreen Probe - should be at the level you consider your tank is too full to be safe to operate. This means that the electrolyte level in the tank is obstructing HHO gas at the top of the tank and the risk of electrolyte leaving the tank through the hose is too high.