Fuel Reserve Sensor
Open Panel

How to repair the fuel reserve sensor, of  XRV 650 and XRV 750 (L to N models, - 1990 to 1992).




The aforementioned XRVs are equipped with two fuel level probes, which indicate respectively the 8,5 lt (orange warning light) and the 4,3 lt, (red warning light) reserves;. Almost always they stop working.

We analyze the problem and suggest a solution.

The probes are nothing else, but thermo-sensitive elements, namely; NTC resistors, that means that the resistance decreases when the temperature is increasing. (NTC = Negative Temperature Coefficient thermistor). Normally, when a current flows through a thermistor, it will generate heat which will raise its temperature higher than its environment; so, when they are submerged into a fluid (gasoline in our case) they are getting cooled, maintaining high resistance; when the level of the gasoline is getting lower and the probes are not into the gasoline, their temperature is getting higher, roughly decreasing their resistance and this will make the warning lights in the control panel to glow.

To repair the probes you first  have to buy an 1 kΩ (1000 Ω) - NTC thermistor.



Remove the probe from the fuel tank and with a thin hacksaw, cut carefully the lower base of it, so you can see inside the burned sensor.

With a soldering iron unsold the lower cable and by heating the upper side of the sensor you can unsold the internal soldering of the thermistor.

Then solder one of the legs of the new thermistor to the internal side of the sensor, keeping the whole part of the thermistor at the middle of the sensor and the other leg to the base of the sensor stem.



Put back the sensor inside the fuel tank and you will have the indication at the control panel.




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