1998 V70 Fuel Gauge never reads full

punkporvida · Post by **punkporvida** » 17 Feb 2014, 16:19

Hey Guys,

I bought this 98 V70 a few weeks ago, and I've noticed that the fuel gauge never reads full. The gauge goes from Zero to 18 Gallons and after a re-fuel it reads 16. It seems to work okay through the rest of the range...

After some searching around i've seen some folks have problems with the gauges getting stuck at random positions, or incorrectly reading empty, but i've seen any issue like the one i'm seeing.

Thanks for you help!
Patrick

Post by **cn90** » 17 Feb 2014, 16:29

Try some Techron...

jonesboy1983 · Post by **jonesboy1983** » 17 Feb 2014, 16:34

I have the same problem with my 850. I have put a bottle of techron in it since I've owned it but that didn't help.

Post by **misha** » 17 Feb 2014, 16:36

Do you fill it up with engine running?

Post by **anodyne** » 17 Feb 2014, 18:10

Mine does the same thing; when full, the needle looks to be about 1/8th below the F mark. I've never pushed the issue, but i'm wondering if the guage will also go about 1/8 below the E mark before it empties? Again, never tried it, but thought about it. I've simply gotten used to it and you probably will too.

MSLV70 · Post by **MSLV70** » 17 Feb 2014, 18:51

Mine does the same. I assume the float gets damaged or gunked up. With an awd, I would need to drop the tank to fix it and that's not happening.

tdlund · Post by **tdlund** » 17 Feb 2014, 20:10

Same thing was happening on my 850 since I bought it. I took out the fuel sending unit and it was smashed at the bottom. I remember the lady who I bought it from said she his a big bump and it had started reading funny. The tank looked fine, since it was plastic, it didn't leave any dents on the outside of it but you couldn't tell the damage on the inside.

Post by **burnout8488** » 17 Feb 2014, 20:18

All I did on my girlfriend's 850 was remove the sending unit and reinstall it. Shook it around when it was out, then retightened the ring pretty snug upon reinstallation.

I think when the fuel tank recall was done on this car, the sending unit wasn't screwed down all the way into the replacement tank, so it didn't read as high. Most of our cars have probably had the recall done.

Just a thought. But after simply R&R'ing the sending unit, her gauge would read totally full after a fill up.

AVIP · Post by **AVIP** » 17 Feb 2014, 21:08

Same thing on my s70. Caused by the pressure in the fuel system especially when hot. I never worried

Post by **jose456891** » 18 Feb 2014, 21:44

The likely cause of incorrect fuel gage reading is the sender unit in the tank (float) is gummed up or stuck. I had the unfortunate fortune of burning the fuel gage on the dash by probing and applying battery voltage to the wrong wire.

Here is a link to my encounters with the fuel reporting system on my 850:
https://www.matthewsvolvosite.com/forums ... =1&t=59470

The following is based on a 1996 850 Wagon GLT, it should be aplicable exactly the same on V70's.

This is what you need in order to test the Dashboard Fuel Gage, and Sender Unit:

10mm Socket + Wrench
DVOM with ability to measure Ohms in the range of 0 to 1000 ohms
1x 500 Ohm potentiometer (variable resistor) available at RadioShack
1x Pair of small aligator jumper cables (the small ones for small circuits, available at RadioShack)

The way the fuel resorting system works is by feeding 7 volts to the sender unit (float). The sender unit is a big potentiometer that changes its resistance according to the fuel level in the tank. There is a physical float that actually floats on fuel. This drives a small arm connected to a connector surface with different resistance values.

This is the specified resistance range according to Volvo: 7.5-12.5 to 322.5-327.5 ohms. The input voltage to sender unit is specified at 7 volts.

Go to the trunk, remove the lining and locate a connector with a YLW/RED and BLK wires. This is the wire responsible for reporting fuel level.

Test for shorts of the power feeding the sender unit:

1) Disconnect the connector
2) Probe the YLW/RED and ground with DVOM. YLW/RED to (+) probe, bare metal pice on car black jumper cable to (-) probe on DVOM.
3) Voltage should be close to 7 DC Volts when ignition is on. If no voltage check for open circuit on YLW/RED or short to ground.
4) Probe BLK wire and ground for continuity. Bare metal on car to black jumper cable to (-) probe on DVOM. BLK wire to (+) probe on DVOM. The resistance should be 3 to 0 ohms. If resistance is infinite or very high, look for damaged BLK wire or open circuit.

Test Dashboard

1) Disconnect connector, do all tests on the connector feeding into the car. Make sure ignition is off.
2) You will construct a ,parallel circuit with the potentiometer, DVOM and car's connector.
3) Stick (+) DVOM probe to YLW/RED conector. Stick (-) DVOM probe to BLK conector. Turn DVOM to ohm scale.
4) Grab a pair of jumper alligator cables.
5) Clip (+) alligator jumper cable between (+) DVOM probe and (+) side of potentiometer.
6) Clip (-) alligator jumper cable between (-) DVOM probe and (-) side of potentiometer.
7) Dial potentiometer to 10 ohms. Use DVOM to pinpoint the 10 ohms.
8 ) Turn ignition on. The fuel gage should read full.
9) Slowly dial potentiometer to 170 ohms. Tank should read 1/2 full.
10) Slowly dial potentiometer to 325 ohms. Tank should read empty. *
11) If fuel gage reads something else other than above, replace cluster.

* it's OK to go past 320 ohms with potentiometer. This will reduce the voltage sent to the cluster down to zero, which its safe. It will probably trigger a check engine light on V70s, on my 850 nothing was set.

Test Sender Unit:

1) Connect DVOM probes to float and set to Ohms. (+) Lead to one wire, (-) to the other, polarity does not matter. If the resistance is not within 7.5-12.5 to 322.5-327.5 ohms, replace/clean sender unit (float).
2) Remove sender unit. Connect to DVOM to sender unit as in step #1. Physically move float up and down, resistance should vary, if not replace float.
3) Set float to position were fuel is highest. Ohms should read 7.5 to 12.5. If incorrect replace sender unit.
4) Set float to position where fuel is lowest. Ohms should read 322.5 to 327.5 Ohms. If incorrect replace sender unit.
5) Slowly move the float arm up and down. Resistance should vary within 7.5-12.5 to 322.5-327.5 Ohms. If there are jumps, drop offs or the Ohm value is stuck for any period of time, your sender unit is dirty. Replace or clean sender unit.

If cleaning sender unit, use kerosene or mineral spirits.

Here is a link to Volvo's own instructions. I like mine better because they are more thorough and applies to 850 and v70's 1993-2000's. No need for special computer equipment.

https://www.dropbox.com/s/5wijz7sll03zf ... 0panel.pdf