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Comment by londons_explore | Hacker News Reader

> the fuel gauge stopped working

This is working-as-intended. Some modern cars only have a very approximate sensor in the fuel tank, and then use computer modelling of fuel use to make the gauge look like it is going down smoothly. After all, the engine knows exactly how many ml it injects with every stroke, so can measure fuel use very precisely - the only unknown is what you are putting in.

Therefore, they assume that you never fill up less than say a half tank. If you fill up less, it will pretend you didn't fill up at all, and the gauge will still say three quarters when it is full to the brim.

The only way to get the gauge and actual tank back in sync is to use up at least half a tank, and then refill all the way.

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This reads like satire, but sadly isn't?

So modern cars have millions of new shiny sensors, but cannot get accurate information on the fuel tank, something my old shitty car reliable can?

I think it's because fuel tank sensors frequently break, due to being buffeted by sloshing fuel, and sometimes getting corroded if there is a little salt water in the fuel, so car manufacturers have decided to use other methods other than a float and variable resistor...

I'm not sure what is actually used instead, but I'd guess they just measure the pressure on the inlet to the fuel pump. An absolute pressure sensor only costs 3 cents and the fuel pump is probably already on the CAN bus.

Back in my day, before all the newfangled shiny sensors you would get an accurate fuel tank reading every time - except if you were going around corners, accelerating or breaking, or had done any of those in the past few minutes and the spring returning the float was feeling slow that day.

Otherwise it was, like all things back in the good old days, incredibly precise +/- 10%

"Otherwise it was, like all things back in the good old days, incredibly precise +/- 10%"

The sad thing is, if todays values are worse.

My first car the sensor was clearly at the back of the tank.

Going uphill? Gauge says 1/4 tank left.

Steep downhill? Out of gas.

Not sure which end the pump was on, but I never ran out despite what the gauge would say.

Ahh yes, how could I forget about the hills, you are giving me flashbacks to the good old days!

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