2006 V70 - Fuel Gauge Stuck on Full

iamhives · Post by **iamhives** » 23 Sep 2018, 12:03

The fuel gauge in my 2006 V70 has been stuck on full despite the tank being about half full. I topped off the tank to see if actually filling it to the top might dislodge the fuel sender float on the theory that maybe it was stuck in the full position. Unfortunately there was no change. I scanned the car with VIDA and found no relevant/active codes. However according to VIDA the left fuel sender was reading 0 litres and the right (fuel pump) sender was reading 70 litres. Since the tank is now actually full does this mean that the left sender is the problem? - seems strange that one sender reading 0 would cause the gauge to read full! Maybe zero is considered the failure mode and hence the full measurement is considered to be most likely? Doesn't really explain why a half tank also shows as full.

Would like to pinpoint the problem so I don't have to open up both sides. Hopefully it is the left side since its is easily accessible from under the rear seat cushion!

Thanks for any input

iamhives · Post by **iamhives** » 24 Sep 2018, 11:56

I started to do some diagnosis. When I opened up the cover under the rear passenger seat (expecting to see one of the fuel senders) I found ... nothing. Basically a blank with a wire emerging (looks like it came from further back) plugged into a socket attached to the floor. I disconnected this (still thinking it might be something to do with the fuel sender) and discovered it was the connector for the rear left ABS sensor (I reset the error code in VIDA). This might explain why the left tank shows as empty ion VIDA while the right tank sensor shows full - since there is actually no left side fuel sender so that may explain that confusion. It still doesn't help fully diagnose the problem but does obviously narrow it to the sender on the right side with the pump.

So based on this finding and a bit more online research it appears there are several configurations of fuel tank (plastic vs steel) etc depending on emissions code and many different fuel pumps, sender units etc. All of the various sources of parts diagrams etc are very unclear/confusing on this with all of the slightly different models/years/emission codes/types of tanks, serial number ranges etc. My car (made late 2005, model year 2006 with 560xxx serial number) has a 2 in the 8th position of the VIN (emissions code 2?) which appears to indicate it has a steel tank (ULEV - ultra low emissions?) which in turn implies it only has one fuel sender which is an assembly that is part of the fuel pump on the right. Also, the believe the seal is not the notched plastic seal that is most often discussed which needs the special tool to undo. I haven't confirmed any of this in reality since its a bit of work to remove the trim, seats etc to get at the fuel pump and I was hoping to get a replacement sender and do the fix all in one shot.

It seems that the fuel sender is typically part of the fuel pump (pump part number possibly 30794624) but VIDA seems to show 8621321 as the part number (again not very clear so I'm not 100% sure this is correct) for the sender alone. This part number isn't even sold by FCP, IPD, Pelican etc and needs to be specially ordered which seems a little strange. It is only $55 so in order to save my time I was thinking of just getting replacement sender vs trying to fix/clean etc the existing one. But obviously that only works if I can confirm the right part number without opening it all up. Can anyone shed any light on this and help me confirm which tank/pump I have and the right part number for the fuel sender.

Post by **cn90** » 24 Sep 2018, 13:26

Try a bottle of Techron FI Cleaner at fuel fill-up.
repeat a few times, this should clean the sender unit.

iamhives · Post by **iamhives** » 24 Sep 2018, 15:06

I'll try that - try the simple things first is a good idea. I have some sitting in the garage somewhere. I also try a little 'persuasion' by tapping the unit to see it that will free it. I'll also have to drive the car a bit so the fuel level goes down since right now really is near full.

Update - I just took the back seat out to get to the fuel pump area. As I suspected above it looks like I have a steel tank which also has the metal locking ring vs the plastic one. There is one connector attachment with a braided harness that exits towards the back of the car and I assume (based on the size and look of the braided covering at both ends) goes to the fuel pump control unit in the rear compartment and a connector that goes towards another connector attached to the floor. Before reaching this connector this splits and goes with a large loose bundle if wires to the rear and has five wires that goes into another connector attached to the floor which then appears to go on towards the front - I suspect this may be the one what has the fuel sender signal and would be the one to test? Anyone know the colors of the wires that are the fuel sender wires coming out of the main connector on the pump cover? - I want to test the resistance are maybe even insert a resistor to make sure the gauge and wiring are OK. I'm suspecting yellow and brown since that are the smaller gauge wires but wonder if anyone knows for sure. The choices are black, blue, smaller gauge blue, yellow, and brown assuming I understand the wiring (which is questionable). Will have to look for a wiring diagram (anyone know of one for a 2006)

Just to make sure I've got this right - high fuel level indication is from higher resistance, correct, while low fuel level is low resistance from the sender? I see some conflicting information online for Volvo's so want to make sure. If true , then a break in the wiring would cause gauge high vs a short which would show as empty?

FCPEuro just replied to a message I sent them and gave me part numbers ' based on my VIN' but I think they got them wrong since I seem to only have one sender and they gave me part numbers for both

Post by **cn90** » 24 Sep 2018, 21:19

Same issue in BMW forums.

This happens b/c some people run fuel low all the time. The evaporated fuel leaves residue behind on the sender unit and gunks it up.

So a bottle of Techron here and there usually fix it.

I also use Liqui Moly FI cleaner (available at Napa auto parts).

I have many vehicles > 150K and have none of these fuel sender issues. This is b/c I usually fill it up to about 90% of the fuel tank capacity and once in a while add some Techron etc.

iamhives · Post by **iamhives** » 24 Sep 2018, 21:29

I never run it low and have used Techron (or similar/Seafoam) in the past on this car so agree with your philosophy.However I have no idea what the prior owner did in the 185k miles before I bought it so hopefully the Techron will loosen up whatever might be stuck

iamhives · Post by **iamhives** » 27 Sep 2018, 15:21

I performed some intricate surgery on the fuel pump/sender unit (with a rubber mallet) and the problem is fixed! As suggested by others I guess the sender was stuck in the max position and a little 'persuasion' knocked it loose. I was about to start to open up the tank but tried this as a last resort. I did learn a little about my car (the fact that it had a steel tank and hence only one sender on the right hand side) so that was useful.

Thanks for the input and helping me avoid spending unnecessary money. I'll try and remember to (and have my family also) not fill the tank to the tip-top.

Post by **cn90** » 27 Sep 2018, 19:37

1+,

I usually fill my car to 90% and stop.

So, let's say I know the gas tank capacity is 17.7G and I currently have 4 G left.
I will fill with approx. 12-13G and stop and the fuel gauge will barely miss the Max mark.

Anyway, a bottle of Techron here and there will prevent it.