Petrol Light Flashing but I Have a Full Tank - What Is Wrong?

Petrol Light Flashing but I Have a Full Tank - What Is Wrong?

With UK petrol station closures sparking huge demand for fuel in recent weeks, motorists have felt acute pressure to ensure they have enough in the tank for essential journeys. But what do you do if your petrol light flashes on your dashboard only for you to discover you already have plenty of fuel on board?

Motorists concerned about inaccurate fuel level alerts are being encouraged to look into the issue and being offered ways to stop this from happening in the future – especially following recent demand for petrol at the forecourts.

The team of experts at are offering insight to confused motorists about why this might be happening to them when driving.

Although the problem of a flashing petrol light can very often appear to be a quick fix, experiences where the light has been misleading to the amount of petrol actually in the tank can leave motorists feeling unsettled about the accuracy of their car’s alerts.

What causes the petrol light to flash?

There is a mechanism called a fuel level sensor which measures the level of fuel within the tank. The fuel level sensor is made up of three components:

  • Float switch: Floats over the fuel quantity to give a physical reading for the fuel level
  • Variable resistor: Connected to the float by a metal needle and measures the variations in the float height
  • Wiper: Moves over a resistive material

When a vehicle’s fuel level changes, the wiper moves across the variable resistance with a metal connecting rod, causing the measure of voltage to change. When the fuel tank is empty, the wiper points to high resistance and vice versa, this is the formula on which the fuel gauge is measured and recorded.

The problem which may cause the petrol light to flash before the fuel tank is actually low is related to the fuel level sensor. Within the fuel level sensor are small metal parts which send the readings to the driver’s dashboard and cause the light to flash. Over time, these metal parts become corroded and negatively influence the mechanism inside the fuel level sensor, resulting in false fuel level readings.

How to avoid it

Dealing with fuel components can be dangerous and should be approached with caution. Motorists who own slightly older cars and are concerned that they may be starting to get inaccurate fuel level readings should firstly refine the type or grade of fuel they are using. Impurities and any water in some types of fuel can contribute to corroding and rust in the fuel level sensor.

Drivers should also not let the fuel tank run out, as filth from the bottom of the tank can get stuck in the variable resistor and lead to issues with the mechanisms, thus leading to inaccurate fuel readings. Drivers who feel as though they are getting completely incorrect fuel readings should seek help from professionals.

Featured T&L Sustainability
T&L 263
T&L 262
T&L 261