Today I discovered that you can use a VAG-COM to adjust the displayed fuel level on the gauge in the instrument cluster. Last year I replaced the fuel level sender on my fuel pump and ever since the indicated fuel level has been off. Specifically, when the fuel tank was filled up completely (pump auto shut-off), the gauge wouldn't indicate a full tank. Instead, the level was just below the full mark, which has been really annoying after spending $70 on a new fuel level sender (which commonly go bad on high-mileage MKIV cars) and spending the time removing the fuel pump from the tank to access the sender.
Well, it turns out that every level sender is a little different and the gauge in the instrument cluster needs to be calibrated to the output from the new sender. Also, an error can develop in the instrument cluster even without a change in the fuel sender and this error can cause the fuel gauge to display the incorrect fuel level. Here's what you can do to fix the problem.
STEP 1 - CHECK THE INSTRUMENT CLUSTER FOR ANY INTERNAL ERRORS
1. Turn the car ignition on, but do not start it. Using the VAG-COM, go into the Instrument Cluster control module (-17-) and select OUTPUT TESTS (-03-).
2. Click on the START/NEXT button to initiate a sequence of tests. The first of these tests the sweep and calibration of the analog gauges. The needles for all four gauges (tach, speedo, coolant temp, fuel level) will drop to 0, sweep slowly all the way to their maximum, and then drop down to a calibration position. These positions are:
Tach - 3000 RPMs
Speedo - 62 MPH (100 KPH)
Coolant Temp - 190°F (90°C)
Fuel Level - 1/2 tank
The Bentley CD indicates that if any of these settings in incorrect, then there is an unrepairable error in the instrument cluster and it should be replaced. All of mine are good, except for the fuel level, which displays just under 1/2 tank. This is obviously part of the reason for my incorrect fuel reading, but I'm not going to pay for another cluster just to fix it. Instead, you can use the VAG-COM to fudge the displayed level.
3. Click the START/NEXT button to cycle through all of the remaining output tests. These tests will check the various warning lights, chimes and LCD displays in the cluster.
4. Keep clicking the START/NEXT button until END comes up, click it once more and then click EXIT to go back to the main menu for the Instrument Cluster control module.
STEP 2 - ADJUSTING THE DISPLAYED FUEL LEVEL
These steps are based on those given in the Bentley CD and are intended to be used after the fuel level sender has been replaced. The proper way to calibrate the fuel gauge to the new sender is to drain the fuel tank, add 7 liters (1.85 gal) of gas, which is the exact amount in the "reserve" tank, and then adjust the fuel gauge needle so that it coincides with the red "reserve" line on the fuel gauge. I wasn't about to go through this, so I filled up my tank and adjusted the needle so that it read full (or as close as I could get it). The VAG-COM allows you to adjust the position of the needle an amount equal to 2 liters of fuel in either direction (+/-) of it's normal factory setting. To do this, do the following:
1. Select ADAPTATION (-10-) on the main screen of the Instrument Cluster control module.
2. In the CHANNEL box, enter 30 and then click on READ. This will display the stored value for the fuel gauge calibration and normally should be 128. You may enter a value from 120 to 136. Each number corresponds to a 1 ohm adjustment of the fuel level sender output and corresponds to 1/4 of a liter. You can use the UP and DOWN buttons to adjust the number while you watch the gauge needle move. If you're doing it the proper way, then adjust the needle until it lines up perfectly with the red mark on the gauge. If you're doing it a different way, like I did, then adjust the needle until it sits where you want it to.
3. Click on SAVE. The new setting is now being used.
That's about it. If you mess something up and want to go back to the original setting, it's 128.