About the HHO Fluid level sensor

How the HHO PROBE / Fluid Level Sensor works and How to modify it...

There are four metal probes on our HHO electrolyte Fluid level sensor. They are made of 316L stainless steel and the tip of the probe at the bottom is what gives the fluid level indication. It works by measuring conductivity of the electrolyte fluid. When the tip of a probe is in the electrolyte fluid it completes a circuit with the reference probe (the longest probe) and gives an indication.

probe color coded image from side without baffle 1probe color coded image from top without baffle cropprobe color coded crop

probe color coded image from bottom without baffle crop

  1. Black: Reference probe or (-) Negative ground probe 
  2. White: Correct fluid level indicator probe
  3. Red: Low fluid level indication probe.
  4. Green: Over full Fluid level indicator probe

1. The longest coloured black in the drawing is the reference probe. Without it, the other 3 cannot work. The other 3 measure the fluid level in the tank (reservoir).

2. The second longest the probe coloured red in the drawings is the probe that when the tip is submerged gives the indication that the fluid level in the tank is too low and the tank must be refilled. If the tip of this probe becomes exposed (not submerged in fluid) the HHO system will automatically shut down and will not restart until it is refiled. This will protect the cell from damage. HHO cells tend to burn out if there isn't a sufficient amount of liquid to circulate through them.

3. The third longest probe coloured white, when the tip is submerged indicates that the fluid level is correct and the PWM will work normally.

4. The shortest probe, when the tip is submerged in fluid will indicate there is too much fluid in the tank. As a result the PWM will automatically switch of if surplus electrolyte fluid is not removed. It switches of to protect the vehicle as electrolyte may pass from the tank through the hose to another part of the car. This is especially true if there is no bubbler installed after the electrolyte tank.


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


1 bar indicates not enough electrolyte in the tank and needs to be refilled.

No bars system will shut down to protect as there is not enough electrolyte for circulation.

3 bars indicate too much electrolyte and HHO system will shut down to protect from overflow.


This indication is also given by the LED lights on the opposite side of the connectors on the PWM.

Starting from left to right the Four LED Indicates:-

1. PWM System ON. Indicated by Green LEDPWM LED

2. Over full / too much electrolyte. Indicated by Blue LED

3. Correct electrolyte. Indicated by Blue LED

4. Too Low / Not enough electrolyte. Indicated by Blue LED


The colours of the probes shown in the drawings also correspond to the colours of the wires that are attached to the top of the probes.

How to modify the HHO Fluid Level Probe

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

A few considerations':-

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

Some types of glue cannot be used to fix the probe to the tank. If the glue is CONDUCTIVE it should not be used. The probe measures electricity and conductive glue will cause a short circuit between the individual probes and therefore it will not work.

You do not necessarily need the plastic baffle for the probe to work. However the probe works better with the baffle if there is foaming in your tank due to too much agitation or oil contamination. One drop of oil is enough to contaminate your electrolyte and cause foaming. The baffle will measure the height of the foam and give a wrong indication. The height of foam is not the height of the fluid. Foaming in your tank is never a good sign.

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 robes 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 preffered.
  3. The Black probe, (reference probe, Longest) has to be at the bottom of the tank but not touching the bottom. A few millimetres to one centimetre of the bottom is enough.
  4. The red probe, (second longest) should be almost as long as the reference probe. A few millimetres to one centimetre shorter than the black is OK.
  5. The White probe (third longest) should be at the height of your tank that you consider electrolyte level as full.
  6. The Green probe, (shortest) should be at the level you consider your tank to be too full to be safe for operating. This means there will not be enough room for the HHO gas at the top of the tank and a danger of the fluid leaving the tank through the hose.


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