2009 TDI has 37,139 miles. This is a salvage that I had rebuilt, minor rear bumper damage along with rear quarter panel an left rear wheel replacement. problem is fuel gauge read full. However, after driving about 40 miles got suspicious as to why it still read full and decided to fill up. It took 14.9 gallons. Proceeded to drive 22 miles and according to fuel gauge it consumed a quarter of the tank. Any suggestions to fix the fuel gauge? This is my first attempt for a thread as I just signed up as a new member yesterday. This 2009 is the third diesel I have owned.
You're going to have to check out the fuel sending unit,but you will need to run the fuel down a bit since you just fueled up. You don't want to try and access the fuel sending unit with a full tank of fuel as you will make a mess.This is best done with a nearly empty fuel tank. Its located under the rear seat on the passenger side of the car. Pull up the seat and you will see that the carpet is cut. Lift up the carpet to expose a black plastic cover. Remove this plastic piece. You will now see the fuel sending unit. Disconnect the electrical connector and the two fuel lines. Now using a screw driver or punch plus a hammer tap the steel locking ring to loosen it. Once its loose spin it off. The fuel sending unit is spring loaded so it will push upwards. Now lift the unit out of the hole being careful to make sure the float arm clears the edge of the hole.
One the fuel sending unit is removed from the fuel tank you can do some test to try and determine what the problem is if there are no immeditate indications as to what may be causing the problem. I'm not sure if the wiring harness is long enough,but if it is plug the harness back into the fuel sending unit and then manipulate the float arm by hand to and watch your fuel gauge to see if the gauge is working with the position of the fuel sending unit float. With the float all the way down it should read empty. Float all the way up,it should read full. 3/4 and so on. Don't expect it to be dead nuts on,but each position should be close and correspond with your gauge. If the wiring harness is not long enough just make a couple of jumper wires that will run from the connector to the terminals on the fuel gauge. You will need 3 jumper wires to jump the fuel gauge wiring which will be the 3 smaller terminals to the inside of the electrical connections. The 2 largrer connections are for the lift pump motor.
Also be aware that once you do all of this you need to refill your fuel tank at least 3/4 before you restart the car.
Hope that helps.
Below pic: fuel sending unit,black plastic cover and steel locking ring.
Below pic: fuel sending unit
Below pic: fuel sending unit with jumper wires on lift pump motor terminals.