[Abs-Zero]

The technical home page of Ian Till

Fuel Computer Tank Calibration

(applies to Cavalier, Calibra, Carlton and Senator)

The fuel tank level sensors fitted to Cavaliers, Calibras etc are all slightly different to each other and so the fuel computer must be able to take account of this in order to provide a useful estimate of range remaining for the fuel level in the tank.  In Vauxhall's TIS software, there's a procedure for calibrating this sensor on the car.  It's only possible to do it on the car, so please don't ask me to correct it on your module when I programme it here. ;-)

I've read the TIS instructions and they are (at best) pretty difficult to understand, so here's my version:

What you'll need:

• Half a paperclip (or a short piece of wire)
• 120 Ohm resistor (you can get these from www.maplin.co.uk order code M120R for about 6 pence)

There are two procedures, this is the most accurate:

1. Working under the car, remove the plug from the fuel tank level sender on the fuel tank.
2. Push the resistor pins into the plug contact holes (on the loom end, not the tank).
3. Working under the bonnet, remove the 10-pin diagnostic connector from it's splash shield.
4. Plug the paperclip into the diagnostic connector between pins A and D.
5. Switch the ignition ON.
6. The fuel computer display has now changed, it should read "d : 1" in the lower display.
7. Press the large Fuel Computer control button repeatedly until this display shows "d : 5"
8. Press in the 'minutes adjustment' key using a pen.
9. The display will change to show " 12L " in the top half and " A   " in the bottom half.
10. Press the large control button again.
11. The top half of the display changes again, to show "120 ", which is the value of the resistor you need.
12. Press the raised control key to start the calibration.
13. The display then shows "- - - -" in the top half until calibration is complete.
14. When complete, the top half of the display shows the range remaining (with the resistor connected).
15. Working under the bonnet, remove the paperclip from the diagnostic connector.
16. Switch OFF the ignition.
17. Working under the car, unplug the resistor from the fuel tank sender loom.
18. Plug the fuel tank sender loom back into the tank sender.

That's it, you're done.

Here's the approximate method for those of you that are too tight to go and buy a resistor for 6 pence: ;-)

1. Drive round until the fuel gauge reads very slightly above the top of the red.
2. Working under the bonnet, remove the 10-pin diagnostic connector from it's splash shield.
3. Plug the paperclip into the diagnostic connector between pins A and D.
4. Switch the ignition ON.
5. The fuel computer display has now changed, it should read "d : 1" in the lower display.
6. Press the large Fuel Computer control button repeatedly until this display shows "d : 5"
7. Press in the 'minutes adjustment' key using a pen.
8. The display will change to show " 12L " in the top half and " A   " in the bottom half.
9. Press the raised control key to start the calibration.
10. The display then shows "- - - -" in the top half until calibration is complete.
11. When complete, the top half of the display shows the range remaining (with the resistor connected).
12. Working under the bonnet, remove the paperclip from the diagnostic connector.
13. Switch OFF the ignition.

It really is worth getting a resistor and doing this properly.  The range function is only as useful as its calibration and one day you might need to be sure how much fuel you have remaining in your tank.  Remember that after a reset, the fuel computer uses a figure of 28.1 miles per gallon for a while until it has measured your driving style and adapted.