Billy Bob

I was experiencing the common "Fuel Sensor Failure" error a week later upon buying my new to me 2002 996TT. There wasn't much information on the web, I hope this will be informative for others. So here are the symptoms that I was experiencing. My fuel gauge would randomly drop to empty with the low fuel light coming on and blink continuously, this would immediately be followed by the message "Fuel Sensor Failure". The range indicator would show - - MPG. After driving momentarily driving this error message would go away and my fuel gauge would indicate a full tank even though the current fuel capacity may be lower. This would occur randomly without any specific trigger. After considerable research I decided to remove my fuel sending unit and take a look at it. I will go over the steps to remove the unit, test it, recondition it and reinstall it. Before you start, please take the appropriate safety measures, since you will be opening up your gas tank you will be dealing with flammable gasoline. This guide is for informational purposes, you assume any risk and responsibility for anything that you do. Tools needed: 1. Several clean towels 2. 10mm wrench, socket (this should be available in your vehicle's tool kit 3. Multi-meter 4. Sand paper 5. Tape or Post-it note Time Required: 30 minutes at a minimum should not take more than two hours. Removal Procedures: 1. Ensure you vehicle is securely parked and that you work in a well ventilated area. Remove the gas cap to depressurize the gas tank. This will minimize any excess gas spillage during removal. 2. Open your front luggage compartment (aka Frunk) and disconnect your battery. Ensure that you have your radio code as the length of the procedure will reset your radio. 3. Remove your spare tire compartment cover to avoid any gasoline to be spilled on it, you will also be standing on the spare tire to get access to the fuel sending unit. The cover is unlikely to support your weight. 4. The fuel sending unit is underneath an oval plastic cover fastened by 4 10mm nuts. It's located right in front of the battery between the factory CD changer and brake fluid reservoir. 5. Remove the nuts and the washers holding the cover, carefully lift the cover and remove it. Clearance is fairly tight so you may need to wiggle it out. 6. The fuel sending unit is now visible, it is white with several fuel line connectors and a harness attached to it. I highly recommend taking a picture of it before removing the connections so that you have a point of reference to compare once you are ready to put everything back together. 7. Remove the harness, squeeze the metal retaining clips, push in and pull out. 8. Remove the fuel lines,squeeze the retaining button, push in and pull out. Note that the fuel lines are color coded which help identify which line belongs where. If you don’t have a photographic memory, take a another picture to aid in reinstallation later on. 9. Now that the connections on top are removed, look for the arrow on the fuel sending unit, it should be on the left side. It will be important to reinstall it back in the same position to ensure the the float does not get obstructed, mark the position with tape on the tank/chassis. 10. You are now ready to remove the black plastic ring that is holding the fuel sending unit in place. Take a piece of tape and place it on the ring in front of the arrow of the fuel sending unit. This will aid in how far you need to tight the ring back during reinstallation. Remove the ring by turning it counter clockwise. 11. Slowly and carefully lift the fuel sending unit up roughly by 3 inches. There is a rubber gasket between the fuel sending unit and the tank so you may need to gently wiggle or slightly twist the fuel sending unit out. 12. Once the fuel sending unit is raised roughly 3 inches, You will see a T shaped electrical harness and 2 plastic fuel lines with one large black connector leading into the fuel tank. This is on the bottom of the fuel sending unit. Remove the fuel lines by pushing the black retaining clip (use the push in and pull out technique as this took the most effort to remove. Gently place the fuel lines in the fuel tank. Remove the T shaped connector by simply pulling it out. Be extremely careful as the wires are delicate. I opted to slip my wrench between the T harness wires to keep it dry to avoid having the harness drop into the gas tank since it harness was not submerged in gasoline. 13. Have your towels ready to capture any excess gas spillage while you slowly lift the fuel sending unit out. Due to the shape and fuel pump cables in the tank below, you will need to slowly and gently maneuver the fuel sending unit out. 14. Place the fuel sending unit on a clean towel on your work bench. Fuel Sending Unit testing procedures: 15. Take note to handle the fuel sending unit gently to avoid breaking it. The wires on the unit are thin and the soldered connections are delicate. 16. With the fuel sending unit on the bench, locate the harness pins on the top of the sending unit. You should see 4 pins/spades. You will be using the 2 small ones in the middle. 17. Take your multimeter and set it to read Ohms. I used the lowest setting on my multi-meter. You will take the two leads on the multi-meter and have them touch the spades on the harness identified earlier. This is where having alligator clips for your leads will be handy as it will free your hands to move the float. while you check the readings. 18. As you inspect fuel sending unit, you will see the float which you can move vertically, on the pivot point of the float you will see a contact panel. During my inspection I noted some play on the float pivot point. The float moved freely vertically, however there was some horizontal play. 19. With the leads on the multimeter move the float up and down and look at the readings. When the float is raised, you should see a smaller number. As the float moves down the numbers should increase. The range I was able to see was 20 when the float was at its highest point and 199 on the lowest point. This suggested that my fuel sending unit was working. If you get a same consistent reading that does not changed or no reading while you move the float up and down, you likely have your self a faulty fuel sending unit that will need to be replaced (roughly $300 or more only available at the Porsche dealership). 20. During my testing, I noticed the readings would fault out to no reading but come back on again. Since I noticed some play at the pivot point where the contact panel was, I took a closer look and saw the contact panel not touching the lead due to the play. I also noticed that the contact panel was oxidized. 21. Take a small piece of sand paper and fold it in to a 1/4 inch tab. You will see two contact sections on the panel in the shape of a crescent moon, one with a flat surface and another with grooves. Gently sand the full surface of the contact point for the one with a flat surface, once the oxidation is sanded off the color should resemble polished brass. For the grooved contact surface, sand in the direction parallel to the grooves. Wipe the surface clean. This should improve the reading consistency in the fuel sender. 22. Carefully bend the float arm to remove the play. Or bend the contact point touching the panel to remove play. This part takes the longest as you need to be extremely careful not to break anything. 23. Once the play is removed, test the sending unit with the multi-meter. The reading will now be consistent and will increase and decrease as you move the float arm. 24. You have completed reconditioning the fuel sending unit, now you can put everything back together. 25. Installation is the reverse of removal. Notes: 26. Once everything is reinstalled, double check that nothing was missed. 27. Before starting your car, remember to allow the fuel pump to prime the fuel before starting when you place the key in the ignition. I opted to prime my car twice. 28. Start your car and go for a test drive. You should no longer see an error and the fuel gauge should be operational again. 29. If you so choose to, take your car to a service center to re-calibrate your fuel gauge. The PIWIS diagnostic tool is required to do this (this is well covered in the forums).30. If you are still experiencing issues, proceed with testing your fuel sensor. If the sensor checks out, you need to get your gauge cluster checked out. 996TT Fuel Sending Unit.pdf