Mine comes on consistenly at 21 miles left to a tank. I don't know what that equates to in km but I'm sure someone knows how to make the conversion.

It's almost 34km.

google.com, search for 21 miles to km

google is AWESOME for conversions

I have driven to ZERO and beyond!!

How to accurately figure out your remaining fuel
 

How to accurately figure out your remaining fuel.

There is only one sure way to accurately calculate your remaining fuel when your light goes on – and it is different for each car and driver.

First off you need to calculate your cars average MPG - And don’t use the cars computer MPG – it is way off!
Take your total miles driven from your last fill up divided by the amount of gallons you just used to fill up your tank. (Take this reading on your average commute cycle)

Next time your light goes on, you need to find a gas station right away and fill er up. At this point you know when your light comes on and how much fuel is left in the tank. Tank is 14.5 gallons on the 2007 Mazda 3 and if I add 12 gallons I have 2.5 gallons left.

Now with 2.5 gallons remaining and I get about 23 MPG in the Speed 3 – this calculates to around 57.5 miles before I’m empty. I have driven 20+ miles past zero and was only able to fill 13 gallons.

Caution / Disclaimer – never let your gas tank run down to zero – you could put yourself and others in jeopardy!

Cheers!

Peter

hi, been reading the boards for a while, but first post.

did the button combo to activate the trip computer.

i run mine past 0 on a regular basis, but i've never emptied my tank. i havent gone far past zero mind you, perhaps 20 miles at most one time. but like a previous poster said, i've ever put at most 13 gallons, and it's a 14.5 gallon tank (according to the manual). also like another poster said, your avg MPG will be off. at the moment mine is sitting at 22.6 mpg but having just filled up today i calculated 25.4 mpg actual for that tank of gas. from the manual, the trip computer calculates your avg mpg from the last time the computer was reset. IE the last time i reset my computer was probably about 2 months ago so that avg MPG includes hi-way driving, city, stop-go-traffic, sitting at idle with the a/c running, etc. from those 2 months.

As far as just the light itself... like i said i filled up today. the light came on just as i was leaving work this evening, i left downtown houston and drove to my side of town (40 +/- miles, and 1.5 hours of stop/go traffic) before i stopped for gas. i put 12.3-something gallons in.

I guess what all this is trying to say is that if your light comes on and/or your getting close to or past zero on the trip computer, dont panic. you *should* have plenty of time to find a station that is the right price/brand/quality/location for you. lol, no need to cut across 3 lanes of traffic to hit the exit ramp at the last second to goto some hole in the wall station that probably hasn't had their tanks tested since they were installed 50 years ago and is a nickle more per gallon than the better place 5 more miles up the freeway ;)