Fuel Gauge/Fuel Level Read-Out Problem

[heydere]

Ahoy !
Happy New Year, Everyone.

Need to fix a fuel gauge/fuel level read-out problem. Problem does not seem to be uncommon, from the little I managed to read across the internet. Note please => home mechanic = no computer diagnostic; frame stands not lift.

Problem: Fuel level gauge incorrectly displays empty when there is approx half-tank gasoline. (Gauge good to approx half way then, toward the less-than-half side, within say 20 miles the gauge shows empty.

From online, the problem could be instrument cluster or the two fuel level sending units or all/any combination of the three.
1) Any plug-in/computer diagnostic that could identify whether cluster or sending units ? I could take to a well equipped independent Volvo shop or (shudder) a Volvo Dealer.

2) Maybe try myself to change the sending units - Difficult to do ? Is one accessible from the top side (behind and remove rear seat ?). The other unit - is this the one on the fuel pump ? Where? Etc...

Please anticipate my questions. In my ignorance of the situation, I don't even know what questions to ask.

Thank you.

All the best,
Richard Cielec
Greater Chicago Metro.

[pbierre]

I've had flaky results with the fuel readout as my 12V battery was starting to fail. You want to rule out a problem with the battery.
Put a voltmeter on, and try to trap the minimum voltage dip during engine startup. If it dips below 12.0V, old battery (combined with cold weather) could indicate the source of the problem.

I might be shooting blanks, but my first instinct would be to grab my ODB-II scanner, hook it up and (when the tank is about 1/4 full) see if the computer is getting a digital input from this fuel level sensor. (It could be an analog sensor??) Is it reading 1/4 tank or near empty? If reading near empty, the problem is the fuel-level send sensor(s). That result would justify exposing the top of the gas tank, and taking out the sensors for inspection/troubleshooting.

I'd place a lower odds on the dashboard gauge being the problem. Not sure how to prove that's the problem, other than to rule out any problem with battery or with the fuel tank level-sender.

[pbierre]

Heydere, I bought the iCarsoft Volvo/Saab i906 ODB-II scanner:

https://www.amazon.com/iCarsoft-iCarSoft-Volvo-Saab-i906/dp/B01N7S5UVF

It has come in very useful. I like this scanner because it is self-contained, you don't need to hook it up to a computer. And, it contains the Volvo-specific diagnostic codes. I would estimate that I've saved $2-3K over the years in shop costs by having this scanner. It plugs in under the dash on the driver's side.

NOTE: I am NOT claiming the scanner will be able to show you the fuel-level as a digital sensor -- that might be wishful thinking -- if the fuel sender/gauge is analog signals, you won't get a readout from the onboard control unit. If you ask me, I could go out and try it on my 20014 XC70 .

As far as getting access to the fuel-level sender, no, you don't have to remove the fuel tank. As per this posting for a 2004 XC70, it is located under the rear set on the right (passenger) side.

Text description:

http://www.volvoxc.com/forums/showthread.php?23937-04-xc70-Rear-seat-removal-help-needed-for-fuel-pump-replacement-access&highlight=fuel+tank+sender

Youtube video:

https://www.youtube.com/watch?v=HVZ1anvz3k4

[pbierre]

Hey, I brought up the Volvo Vehicle Communications Software Manual

https://www1.snapon.com/display/3871/Volvo_VCS.pdf

from 2013, and there are dozens of parameters reported out by the computer, but unfortunately, fuel tank level is NOT on the list.

So, the ODB-II scanner isn't going to help diagnose this specific problem.

[heydere]

Thank you for the information. Most helpful.
I've am not familiar with ODB's but, it is way past time I purchase and learn how to use one.
All the best,
Richard Cielec
Greater Chicago Metro

[Krajowy]

I had this problem over two year ago with my 2005 Volvo XC70. I fixed it with a very gentle sanding the fuel-level sensor copper contacts with a very fine sanding paper (2000 I think). I started with the one without the fuel pump and it did not cure the problem.
Cleaning the fuel-level sending unit attached to the fuel pump finally resolved the issue. One needs to gain the access to the fuel tank from the top (a pump removal tool is necessary). The fuel-level sending unit contacts were visibly oxidized or covered with black gunk.
I would do it with almost empty tank and start with the fuel pump side.
Here is a link https://www.youtube.com/watch?v=-egNDgTdUYE to the cleaning but I would be more aggressive and do it with a sanding paper as it will create a uniform contacts’ level.