Fuel Gauge - Erroneous Reading

[72dudes]

Last night the fuel gauge read just under one quarter full (as it should be). This morning, it's reading about one third full and the fuel computer has added about 100 miles to the "distance to go" readout.

So unless Santa has paid an early visit and snuck some diesel in my tank, something's not quite right.

 

All other gauges and switches are fine - the only unusual thing is that the Trafficmaster woman has started saying "license expired" every time ignition is switched on.

 

FIlled up with diesel and fuel gauge shows full.

 

Any ideas? Sticky sender unit which is now OK after fill up, or something more tricky?

 

Thanks.

[kfk]

Operation stages : When the ignition is switched on . The instrument panel compares the last fuel level displayed with the gross level indicated by the fuel sender unit (variable resistor fitted with a float) . If there is a significant difference (about 10 litres), the gross level information is displayed, otherwise the last fuel level displayed remains .

Operation stages : When driving . The fuel sender unit is no longer used . The engine management ECU supplies the fuel flow information to the BSI . The BSI encodes this information in a VAN frame . The instrument panel takes this consumption information into account to calculate the fuel level . The instrument panel sends this level to the BSI via the VAN network . Special cases : Low fuel warning . Below a certain sender unit value, the instrument panel sends the minimum fuel information to the BSI via the VAN in addition to the fuel level in order to warn the engine management ECU . In addition, the instrument panel displays the warning message : "LOW FUEL WARNING" . The warning lamp is illuminated .

 

If you parked you car on a slope/2 wheels on pavement this too can alter the fuel level and cause the type of problems you reported.

[72dudes]

Thanks for that kfk.

 

Car was parked on flat surface in garage before this happened. Fuel gauge read 1/3 full both when ignition was switched on and during driving. Stopped engine and switched ignition back on 3 times, fuel gauge still read 1/3 full.

 

Filled up (51 litres) means approx 14 litres was still in tank - corresponds normally to just under 1/4 on gauge.

 

When switched on ignition after filling up, gauge paused at 1/3 for a moment, then shot up to full (this would be explained by your last fuel level/gross fuel level).

 

So I'm still not sure why this happened - could the float have become lodged temporarily, or is the variable resistor breaking down?

[kfk]

Could be either of your suggestions in the last sentence........could also be a one off blip that isnt worth loosing too much sleep over........after all to try and fix it you now have to work out what to do to recreate it!

 

Also, i wouldnt start removing the fuel tank sender to have a look on the off chance of seeing a fault.......chances are you will have trouble getting the locking ring back on that holds the gauge in place, for some inexplicable reason undoing the ring allows the tank thread to become oval.......so only remove the tank unit if you know you have a fault.....oh and make it an empty tank as it reduces the weight in it which minimises the chance of the aperture going oval.

[72dudes]

Could be either of your suggestions in the last sentence........could also be a one off blip that isnt worth loosing too much sleep over........after all to try and fix it you now have to work out what to do to recreate it!

 

OK - that's what I wanted to hear!

Many thanks.