Fuel gauge not knowing the tank was filled

[wfwright2]

U. S. 2002 4.4, 190000 mi. Has a recurring issue where the gauge does not show full after a fill-up. It does continue to function as if the 20 gallons of fuel was not just added. It continues to mark decreasing level of fuel as the vehicle is driven and even turns on the low fuel warning light. Of course the range reading matches the gauge. So far it discovers the error after a number of restarts and returns to accurately displaying tank level. Is it me or is the car loosing its mind?

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[davintosh]

You'll probably need to replace the in-tank pump & level sensor assembly. We had a similar problem with our X5 earlier this year (while on vacation, of course) and had the thing quit on the highway. It had either run out of gas (when it said we had over a 1/4 tank left) or the pump overheated. The shop we ended up at had a tough time diagnosing the issue, and it ended up being far more expensive than it should have been. Ours had ~170,000 miles on it.

Keep in mind there are two sensors -- one side has the fuel pump and sensor, and the other has just the sensor -- because of the design of the tank, which straddles the center of the car and has to clear the driveshaft & exhaust.

RealOEM.com * BMW E53 X5 3.0i Fuel pump and fuel level sensor

[wfwright2]

What I do not understand is that the gauge continues to operate and send signals to the OBC, just from the level where the tank was when filled, I.e. when tank is filled from 1/4 full, the gauge then continues the consumption tracking as if no fuel was added. Like it is never told that the tank level is now full.
No indications of a failing pump so far - always starts and no hesitation under WOT operation. All of fuel system, less filter/regulator are original.
Of course when it feels like it the car will figure that there is a full tank and provide proper level indication.
I do try to keep tank above 1/4 to provide liquid cooling to the pump, failed Jeep pump (with full tank) taught me to be careful with these in tank pumps - no problems yet with my high milage BMWs.

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[TerminatorX5]

davintosh is correct, it is probably something in the active or passive pumps assembly...

since the issue is intermittent and sometimes the gauge is working (it is, right?), the problem could be electrcial.

pull the rear seat up - with middle seat belt extracted completely out, and secured, so it does not roll back into the car, put your hand on the edge of the rear seat, if there were a passenger, the hand would be between the legs of imaginary passenger, and YANK it vertically up for the pin to disengage, do the same for the other "passenger". pull the seat from the back and tilt it towards the front seat, while feeding the middle belt through the hole, so it is out the way.


what you will see there, is bunch of wires, depending on your options list... check the wires for being loose, for chaffed insulation (less likely but possible), especially check the grounding block for rust or loose connection... wiggle wiggle some wires, see what happens... this is the cheapest route at this stage...

to put the seat back, feed the seat belt buckles back into the seat, and JUMP on those pins so they engage again...


very simple procedure, no tools needed

[TerminatorX5]

it also can be a float inside the pumps... could be stuck... needs a good whack with a sledg.. uh... an R/R... lol

pull your OBC computer reading and see what each of the sides is reading - the total displayed by the needle is the sum of two halves of the tank, so the OBC reading may show you one is reading ZERO, and will allow you to narrow your attention to that part of the tank...

[Qsilver7]

If your cluster is unlocked...you can also do TEST 6 to see the input data that the fuel level sensors are sending to the IKE (instrument cluster).

There are 2 screen displays for TEST 6. One gives the data from each sensor (left/right) + the approx total of fuel (in liters) remaining in the tank. The 2nd screen gives an approx total of fuel (in liters)...and a Phase 1, 2, or 3 that reveals if one of the sensors is faulting, if both are faulting, or if the sensors are okay.

You can do this at anytime but also while driving around or when you fill-up...to see which data is incorrect, or at what point the data becomes accurate or inaccurate.

You can see the examples of TEST 6 from my e38's instrument cluster. UNFORTUNATELY...the e53's fuel tank isn't evenly bifurcated like the tanks on the e39/e39/e46...the left side (driver's side) is larger than the right...so the numbers you see for the left/right fuel level sensor won't be "equal" like in the example below from my e38's instrument cluster:

See TEST 6 (below) for info as to what the 2 screen displays indicate















(again, the left side of the e53 gas tank is different than the right)

[TerminatorX5]

Q, do you have any relation to Q (Quartermaster) from James Bond?

As always, you have come through with excellent explanation!!!!

[Qsilver7]

Originally Posted by TerminatorX5

Q, do you have any relation to Q (Quartermaster) from James Bond?

As always, you have come through with excellent explanation!!!!

LOL...I was trying to tie my info in with your post...but I see that you got a chance to post again with the info I was gathering.

Another thought to the OP...if you do TEST 6 and it appears the fuel sensors may not be registering correctly...some have run a tank of Techron (spelling ?)...to see if that can clean up some deposits that may be causing them to gum up and not articulate (move) through their entire range.

[wfwright2]

This morning, before getting to do the OBC/OBD tests, the gauge read properly - full, I really dislike intermittent issues!

[wfwright2]

I run a fuel system cleaner with almost every fill-up. Techtron is the most reliable cleaner on the market.