Cadillac Owners Forum banner

1 - 20 of 43 Posts

·
Registered
2009 CTS-V
Joined
·
931 Posts
Discussion Starter #1
The "Fuel Used" gauge on my Info is way off, i.e. it shows 10 gallons used when it takes 14. I've checked it several times and it's way off. Before I bring it to the dealer, I'd like to know what the fix might be so I don't have to have them make me come back a second time.
 

·
Registered
05' CTS-V
Joined
·
3,718 Posts
hmm wierd...I know the fuel used is the only accurate thing on my car...the in-dash gauge is useless, so is the remaining miles....but, I don't think there is a specific sensor for it...I know there is a TSB out on inaccurate fuel readings...being an 04' I wonder if your car is experiencing that, and if the fuel used could also be attributed to that.
 

·
Registered
2009 CTS-V
Joined
·
931 Posts
Discussion Starter #3
hmm wierd...I know the fuel used is the only accurate thing on my car...the in-dash gauge is useless, so is the remaining miles....but, I don't think there is a specific sensor for it...I know there is a TSB out on inaccurate fuel readings...being an 04' I wonder if your car is experiencing that, and if the fuel used could also be attributed to that.
I looked at the list of TSBs on FAQs and couldn't find any reference to this. Do you have a date, # or other info that could help me pin this down?

Thanks!
 

·
Registered
2015 BMUU 335i MSport, 2006 STS-V--2005 CTS-V ( traded in)
Joined
·
25,514 Posts
I have to manually reset my fuel used info after I fill the car up ?

My fuel used is fairly accurate, usually off by only about 1/2 gallon.
 

·
Registered
Joined
·
2,180 Posts
I believe that the computer merely calculates the fuel used by dividing the miles by the average fuel economy, since the last reset. If your trip odometers are accurate, and your average fuel economy is accurate, then your "fuel used" should be accurate.

Mine are all accurate.
 

·
Registered
Cadillac
Joined
·
36 Posts
Not to hijack the thread, but my cals are all messed up too. At 1/2 tank on the analog guage I have a DTE of 120 miles and my fuel used is 10.2 gal. However, my trip counter was already at 170 miles. I haven't had the car long, but I've filled up 3 times and all three times I've made it about 210 miles per tank.
Why do I get 170 for the first 1/2 tank and 40 miles for the second? I'll keep an eye on the gallons used as it get's near E.
 

·
Registered
2009 Z06 / 2013 F150 EcoBeast / 2008 Twin-Turbo Bimmer
Joined
·
4,860 Posts
The fuel burn indicator is adjustable in the PCM. It would be very strange if the value was changed from the factory default.
 

·
Cadillac Technician
none
Joined
·
11,051 Posts
The key word here is "approximate".
The information on fuel usage is all calculated based on when you reset it and the approximate fuel level in the tank based on the readings from both sensors.
There are two fuel level sensors in the CTS and CTS-V fuel tank. The computer watches them both and uses data tables to calculate the fuel quantity based on the voltages from the sensors.
Software controls the reading since values can fluctuate during driving due to fuel slosh and without a "buffer" the values will fluctuate wildly.
You must reset the values anytime you are doing real mileage monitoring.
It does not reset by itself when you fuel up.
(as far as I know anyway)
 

·
Registered
2009 CTS-V
Joined
·
931 Posts
Discussion Starter #13
The key word here is "approximate".
The information on fuel usage is all calculated based on when you reset it and the approximate fuel level in the tank based on the readings from both sensors.
There are two fuel level sensors in the CTS and CTS-V fuel tank. The computer watches them both and uses data tables to calculate the fuel quantity based on the voltages from the sensors.
Software controls the reading since values can fluctuate during driving due to fuel slosh and without a "buffer" the values will fluctuate wildly.
You must reset the values anytime you are doing real mileage monitoring.
It does not reset by itself when you fuel up.
(as far as I know anyway)

No, it does not reset by itself. I'm talking about when I reset it. That's when it's off by as much as 40%.
 

·
Cadillac Technician
none
Joined
·
11,051 Posts
I suspect there could be room for some error in the way the fuel amount is calculated and I know that there is a portion of the tank that is not measurable once it reaches a certain level. From there it is up to the PCM programmer to decide how the ECM is measuring how much fuel you have.

There are no bulletins regarding a concern like this.

Perhaps you should verify a department of agriculture weights and measures certification on the pumps you use to fill your car.

Have you ever run out of gas with the gage still showing that you have some? That is the only problem I have seen with any CTS fuel system, except a few rare outright pump failures.
 

·
Cadillac Technician
none
Joined
·
11,051 Posts
If one of the sensors is bad the computer should be able to detect it, when that happens it usually sends the fuel gage to empty and puts on the low fuel light (depending on the failure).
They are pretty good about not lying to the ECM by giving wrong data due to the way they are designed and the way the computer monitors them for faults.

Typically the fuel transfer problem causes you to run out of fuel with 1/4 tank showing on the gage.
 

·
Registered
2009 CTS-V
Joined
·
931 Posts
Discussion Starter #17
If one of the sensors is bad the computer should be able to detect it, when that happens it usually sends the fuel gage to empty and puts on the low fuel light (depending on the failure).
They are pretty good about not lying to the ECM by giving wrong data due to the way they are designed and the way the computer monitors them for faults.

Typically the fuel transfer problem causes you to run out of fuel with 1/4 tank showing on the gage.
I think this also has something to do with track usage. Back in 2004, I ran out of gas on the track twice when it showed more than 1/4 tank. In both cases, I was able to restart the car after sitting for a couple of minutes.

After that, I started using the "Fuel Used" guage whenever I was at the track. So as soon as it showed 10 gallons or so, I would refuel. But last week at Pocono, I noticed when it showed 10 gallons used, it was taking 14 gallons to fill it. The Fuel Used was off every time, by as much as 40%. I filled it myself each time right to the spout.

That's why I made the original post.
 

·
Cadillac Technician
none
Joined
·
11,051 Posts
Well it sounds like you might have an issue with the fuel transfer.
You need to make sure your dealer knows you have been running out of gas with 1/4 tank on the gage, if you tell them you are having problems with the fuel used display they might not do much.
If you tell them you are running out of gas, they will probably fix it.
 

·
Registered
ZIP
Joined
·
51,864 Posts
I think this also has something to do with track usage. Back in 2004, I ran out of gas on the track twice when it showed more than 1/4 tank. In both cases, I was able to restart the car after sitting for a couple of minutes.

After that, I started using the "Fuel Used" guage whenever I was at the track. So as soon as it showed 10 gallons or so, I would refuel. But last week at Pocono, I noticed when it showed 10 gallons used, it was taking 14 gallons to fill it. The Fuel Used was off every time, by as much as 40%. I filled it myself each time right to the spout.

That's why I made the original post.
Whew! I dipped under 1/4 tank at VIR and had no problems. I think trukk and MWD did the same, we all had to refuel at the same time. Our Vs were thirsty. They don't have '04s but I do.

*Note to the memory banks...
 
1 - 20 of 43 Posts
Top