LPFP Replacement, Fuel Gauge Calibration?

[cnxoxo9]

Hello! I have a 2014 Audi Q5 2.0T and recently replaced a LPFP. I replaced it after driving it a month ago in 100+ temp outside and it shut off on me while driving. I pulled the following codes, P0089 and 02636. Replaced the LPFP with a VDO Continental. It has been driving great the last few weeks but my fuel gauge will stay at full until I drive about 100 miles then it will start dropping. I pulled the LPFP out just to make sure that the leveler wasn't getting caught in something and it looks fine. Is there an adaptation I need to do to recalibrate it? I'm using Carista but it doesn't have an option for that but don't want to get VCDS unless that is the only option. Thanks!

[Smac770]

There's two level sensors in the quattro fuel tank. The upper one covers the top 1/4 of the tank range, the one at the pump covers the lower 3/4 of the tank range. Did you forget to reconnect the rear sensor to the fuel pump flange? The workshop manual for the "fuel supply system" has how to test the resistance on the level sensor pins. Resistance measurements; the pin arrangement is not the same between the B8.0 Bosch pump and the B8.5 VDO pump.

https://www.audizine.com/forum/showt...1#post14915064

[cnxoxo9]

There's two level sensors in the quattro fuel tank. The upper one covers the top 1/4 of the tank range, the one at the pump covers the lower 3/4 of the tank range. Did you forget to reconnect the rear sensor to the fuel pump flange? The workshop manual for the "fuel supply system" has how to test the resistance on the level sensor pins. Resistance measurements; the pin arrangement is not the same between the B8.0 Bosch pump and the B8.5 VDO pump.

https://www.audizine.com/forum/showt...1#post14915064

Thanks @Smac770. I double checked the connections when I checked on the float arm the 2nd time. It looked good. I'll check on the resistance this weekend to see what the measurements I get.

[q5 dave]

Did it act different before the swap? My 3.0T will stay pegged at full for 70ish miles before slowly dropping.

[cnxoxo9]

It did. I really notice it in the digital how much fuel to empty gauge where it would stay at 465 miles left and not move until I drive for atleast 100 miles then it will move to 460 then start dropping normally.

[Smac770]

So Q5 tank is different from A4/A5, not only in size.

The Q5 fuel tank is 20 gal, compared to 16 gal for the A4/A5. But it also appears the Q5 does not make use of the dual level sensor configuration like the A4/A5 have to utilize, probably due to the extra subfloor height to work with. This would explain why the Q5 workshop manual explains how to test the level sensor G but not the additional level sensor G169. But doesn't explain why Audi still draws the G169 sensor in the Q5 wiring diagrams, which is why I expected both sensors.

Testing the Q5 fuel pump electrical reading.

There doesn't seem to be any copy of the B8 Q5 (type 8R) Fuel Supply System workshop manual for gas engines out on the Internet, not even at cardiagn.com. Only the one for diesel engines. I'm not about to drop $35 at erwin to pick up a manual for a vehicle I don't have. This is the title and index pages for the document that would be the correct one: https://erwin.audiusa.com/erwin/D3E8...ticleId=156214

So the fuel pump for the B8.5 Q5 2.0T flex fuel engine is 8R0919051E, and it's only going to have a 3-pin connector for the fuel level sensor, rather than a 6-pin, such as in the link I posted previously. The concept is the same, as is the 340Ω range of the potentiometer, but the pins are different and there's no sensor 2. In the diesel manual, we get the following for the empty/full resistance values (left having to assume it's the same for the Q5 gas fuel tank, which is the same config and size):

– resistance between pins 1 and 2:
• Fuel tank empty: approximately 285 Ω.
• Fuel tank full: approximately 60 Ω.

– resistance between pins 1 and 3:
• Fuel tank empty: approximately 60 Ω.
• Fuel tank full: approximately 285 Ω.

– resistance between pins 2 and 3:
• Fuel tank any level: about 340 Ω.

Those are for the sensor installed in the fuel tank. If you remove the pump/sensor so it's free hanging, the manual says the 60Ω should be more 53Ω. (you can move the arm higher up manually than a full tank level would) But also note to establish a correct full measurement with the pump installed, the manual notes, "The fuel tank must be filled completely in order to have an exact reading of the resistance on the “Fuel tank full” when it is installed. Drive at least 500 meters (0.3 mile) after filling the fuel tank full to get rid of any bubbles in the fuel tank. Then fill the fuel tank again."

The single sensor configuration certainly makes it easier to assess the situation.

Adjusting the instrument cluster gauge.

So turns out you can tweak the fuel gauge on the instrument cluster by adjusting adaptation values. If you go into the J285 (17-instrument cluster) and then to adaptations, adaptation channels 30 and 33 are the relevant ones (on my B8.0 A4 2.0T). I expect all the B8 to be similar. Seems it was 29 and 30 on prior generations like the 8E A4 (B6 and B7)

Adaptation channel 30 is "tank characteristic (fuel level sensor 1)". This sets the low end of the gauge. It is a number in the range of 128±32. Each adjustment from 128 represents an adjustment of 1Ω, which represents roughly 1/4 L, or 1/15 US gal. So basically that means you get an adjustment range of roughly ±2 gallons. From what I can find, the correct way to set this is to drain the tank empty, then add exactly the reserve volume (2.6 US gal for 8R Q5), then adjust the value so the needle is right at the red marker (which has always just been 1/8 tank to me). I've never toyed with it, the value is 117 on my car.

Adaptation channel 33 is "tank characteristic (full calibration)". This sets the top end of the gauge. It is a number in the range of 128±16, so only half the adjustment range of the other adaptation. So you may or may not be able to account for being off by ~100 miles (I assume that's about 4 gallons). I guess you could try a number outside the range and see if it takes it. Also, when you do the adaptation, you'll want to make sure the tank is full per the workshop manual note shown in the previous text. You'll want to have a laptop or mobile so you can do the adjustment right after the second fill up. I've never toyed with it, the value is 128 on my car, and I get about 25-40 miles (1-1.5 gal) before the needle moves, depending on what station/pump/time of day/etc. Ie, how really full did the pump fill the tank.