EagleTribune.com, North Andover, MA


November 10, 2012

Car's gas gauge can't be trusted

I have a 2005 Scion XA with 45,000 miles. I am the original owner. My problem is my gas gauge. In the past year, it has failed twice to indicate the amount of gas in the tank. This goes on for about 4-5 days and then it clears itself and operates like nothing happens. Is there an additive that I can put in with my gas to clean the sensor in the tank? Is there a mechanical fix I could do? The gas I use is Sunoco 89 Octane.

Your Scion employs an integrated fuel pump/gauge sending unit within the tank to deliver fuel to the engine and indicate fuel level. You didn’t mention what the fuel gauge indicates when it’s misbehaving, so we’ll look at all three possibilities.

If the needle reads too low or drops to empty, this could be caused by a faulty electrical connection — such as an open circuit or high resistance — either within the sending unit or somewhere between the sending unit and the instrument panel. If the needle rises to full or beyond, a short to ground in this same circuit could be the cause; it’s rare but possible. If the gauge continues to indicate perhaps one-quarter full, yet you run out of fuel, the sending unit’s float arm may be hanging up on the fuel pump’s strainer sock; it may be mispositioned or has become distorted in shape.

It’s unlikely a fuel additive would help restore proper gauge function. During one of these episodes, a quick test of the gauge circuit can be made by removing the back seat lower cushion and accessing the fuel pump/sender electrical connector, beneath the fuel tank access hatch. If opening the gauge circuit (unplugging the connector), then jumping the violet to brown wires of the car-side of the connector together results in an empty, then full gauge reading, the fault is within the sending unit.

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