How to calibrate Fuel Gauge?

**PatO** · 01-16-2005, 08:42 PM

Ever since I bought my Jeep about a year and a half ago, the fuel gauge has been substantially off. It's fine when full, but reads Empty when the tank still has over 5 gallons left (around 1/4 full, about 100 miles @ 20mpg).

It's not that big of a deal, but is somewhat irksome when on long trips or if I don't hit the gas station every two days... Does anyone know how to calibrate it? Is it an OBD thing? Or does the dash have to be cracked open? Dare I ask what a dealer would charge to do this?

Thanks in advance,
-Pat

**wizardPC** · 01-16-2005, 10:48 PM

I had a chevy pickup years ago with a similar problem. It ended up that I had to replace the fuel sender. Since my fuel sender was part of my fuel pump, which was located inside the fuel tank, which was between the bed and the driveshaft, my warranty company ended up paying about $800 for parts and labor to fix my fuel gauge

Good luck!

**PatO** · 01-17-2005, 02:02 AM

That's NOT what I wanted to hear!

I did some searching and it seems that the sensors are calibrated with resistance... The articles got me thinking about when it's the most inaccurate, and it seems to be a steady rise in innacuracy between full (most accurate) to empty (most inaccurate). Since the guage is calibrated at two points (full, empty), I "ThinK" the empty calibration is off.

Now the question is - how is it calibrated? OBDII or by some other means?

**carpcnoobie** · 01-17-2005, 06:38 AM

Not sure if you're aware of this, but fuel tanks are designed with a certain amount of reserve, so that could account for your gauge being accurate.

Also, fuel gauges purposely lie. They are full, that is pretty much correct, but if you've ever noticed how the gauge will stay at full for a long time, then start to go down, then when you get near empty the gauge seems to rush towards "E"? That's purposely built into fuel gauges. This is done to 'trick' the driver into thinking they're about to run out of fuel any minute and should refuel soon.

Cadillac had a car in the 80s that had a digital read-out that showed the number of gallons in the tank. The problem was that it showed the accurate number. People started complaining about poor fuel economy because it wouldn't stay full very long.

BTW,fuel senders in the tank tend to go on the expensive side. And yes, you're right. It is based off of a resistance, between 70 an 90 ohms for GMs.