2005 A6 - Fuel gauge goes up - how many fuel level sensors?
03-04-2017, 08:02 PM
#1
AudiWorld Member
Thread Starter
2005 A6 - Fuel gauge goes up - how many fuel level sensors?
I am still sorting out a few things on my new to me 2005 A6. One really annoying problem is the fuel gauge. It will occasionally drop a bit but primarily goes up. I have done quite a bit of troubleshooting and I think it is most likely the fuel level sender. Troubleshooting so far:
Performed VAGCOM instrument cluster test
- All gauges went to half way. Test results normal
Used VAGCOM to graph fuel level readings and sensor 1 resistance during a drive
- VAGCOM has one measuring block that is a constant for tank volume - 80.3l
- I used VAGCOM measuring block 26 to read fuel sender resistance and fuel volume left
- Fuel volume reading would go down around corners (sloshing) and go back up when braking
- When it comes back to steady state, the resistance will be lower and fuel volume will show higher than 80.3l (e.g. fuel gauge will go up)
I pulled the fuel pump assembly to check for obvious problems
- Made a fuel tank lock ring tool instead of buying one since I was impatient
- Siphoned the ret of the fuel out
- Exercised the fuel level sensor and it seemed to get "Stuck" at some points until I moved it all the way up or down and then it seemed to start reading normally again
Put everything back together and fuel gauge showed pretty much empty. Miles left as reading 0. Made it to the gas station and put in 1.85 gallons. That should be the volume to read at the bottom of the red on the gauge. Gauge went to ~1/4 and miles left was reading 60. Drove a little bit and gauge started going up and miles left started going up. By the time I got home (2 miles), miles left was 115.
I think ether the sender is bad or I have a gold mine on my hands and my car can manufacture gas! I took the entire fuel pump assembly out (didn't take any pics) and was able to take the float assembly out. It's pretty well closed and I didn't want to pry to hard to open to see if there was a problem inside.
The one thing I did not do before I put everything back was to check inside of the tank opening on the drivers side.
The one question I have: It looks like there is another level sensor on the drivers tank side. I know there's pump on that side. Is there a sensor there and if so, how do the two sensors work together? When I hooked up the passengers side one and moved it up and down, the gauge seemed to respond over the full range.
Performed VAGCOM instrument cluster test
- All gauges went to half way. Test results normal
Used VAGCOM to graph fuel level readings and sensor 1 resistance during a drive
- VAGCOM has one measuring block that is a constant for tank volume - 80.3l
- I used VAGCOM measuring block 26 to read fuel sender resistance and fuel volume left
- Fuel volume reading would go down around corners (sloshing) and go back up when braking
- When it comes back to steady state, the resistance will be lower and fuel volume will show higher than 80.3l (e.g. fuel gauge will go up)
I pulled the fuel pump assembly to check for obvious problems
- Made a fuel tank lock ring tool instead of buying one since I was impatient
- Siphoned the ret of the fuel out
- Exercised the fuel level sensor and it seemed to get "Stuck" at some points until I moved it all the way up or down and then it seemed to start reading normally again
Put everything back together and fuel gauge showed pretty much empty. Miles left as reading 0. Made it to the gas station and put in 1.85 gallons. That should be the volume to read at the bottom of the red on the gauge. Gauge went to ~1/4 and miles left was reading 60. Drove a little bit and gauge started going up and miles left started going up. By the time I got home (2 miles), miles left was 115.
I think ether the sender is bad or I have a gold mine on my hands and my car can manufacture gas! I took the entire fuel pump assembly out (didn't take any pics) and was able to take the float assembly out. It's pretty well closed and I didn't want to pry to hard to open to see if there was a problem inside.
The one thing I did not do before I put everything back was to check inside of the tank opening on the drivers side.
The one question I have: It looks like there is another level sensor on the drivers tank side. I know there's pump on that side. Is there a sensor there and if so, how do the two sensors work together? When I hooked up the passengers side one and moved it up and down, the gauge seemed to respond over the full range.
03-05-2017, 02:43 PM
#2
AudiWorld Member
Thread Starter
I took the other cover off today to see what was inside. As expected, there is a pump and a float. This side is defintiely different. The float seems to live it's life outside of being immersed in gasoline it's entire life. I took the float out and unsnapped the cover. Everything was pretty clean. I checked the resistance level and this one only read in the upper half of the float range. In the middle where it started reading, it was ~52ohm. At the upper end it was ~195ohms. This float has wires that run over to the passenger side connector. Each float has a different wire to the connector.
Once I checked this one out, I took the other side back apart to check that float. It also only read resistance in the upper half of the float range. It had the same readings as the other one for resistance. I took the passenger side one apart and it had some crud buildup inside the float mechanism but nothing that seemed obviously wrong.
One thing to watch for if you take the float apart is a very small square magnetic piece that goes in the end part of the float. It runs against the resistance pad. I didn't know it was there and accidentally dropped it onto the driveway. Took about 10 minutes to find it.
After taking everything apart and putting it all back together, the gauge actually went up again and the resistance reading from VCDS was even higher. The measuring block for the two level sensors only shows reading for fuel level sensor 1. The values for fuel level sensor 0 are always 0. I'm guessing that somehow the two floats get combined into a single reading for the gauge.
There isn't much left for me to check at this point so I am going to try getting a replacement float for the passenger side first. If one of those floats were to go bad, I would guess it would be the one sitting in gas all the time.
On the plus side, the lock rings come off a lot easier now. It was a bitch getting both of them off the first time. I guess after 12 years, everything swells and fuses together.
Once I checked this one out, I took the other side back apart to check that float. It also only read resistance in the upper half of the float range. It had the same readings as the other one for resistance. I took the passenger side one apart and it had some crud buildup inside the float mechanism but nothing that seemed obviously wrong.
One thing to watch for if you take the float apart is a very small square magnetic piece that goes in the end part of the float. It runs against the resistance pad. I didn't know it was there and accidentally dropped it onto the driveway. Took about 10 minutes to find it.
After taking everything apart and putting it all back together, the gauge actually went up again and the resistance reading from VCDS was even higher. The measuring block for the two level sensors only shows reading for fuel level sensor 1. The values for fuel level sensor 0 are always 0. I'm guessing that somehow the two floats get combined into a single reading for the gauge.
There isn't much left for me to check at this point so I am going to try getting a replacement float for the passenger side first. If one of those floats were to go bad, I would guess it would be the one sitting in gas all the time.
On the plus side, the lock rings come off a lot easier now. It was a bitch getting both of them off the first time. I guess after 12 years, everything swells and fuses together.
03-07-2017, 04:38 AM
#3
Thanks for taking to time to explain your problem and share your discoveries.
I think I had this problem twice and both times it was right after adding injector cleaner to an almost empty fuel tank before topping off the fuel. In my case, the gauge wouldn't move up immediately. It would move to the normal level only after hours of driving. Once set, everything works fine later on. But that was not normal.
I suspected the injector cleaner so the next time I added fuel injector cleaner, I made sure to fill the fuel tank at least to half the tank capacity before adding the fuel injector cleaner and then topping off. With this method, everything worked fine and I've never experienced the problem again since.
Maybe your fuel system is dirty and needs cleaning. What about using fuel cleaner for some time and see what happens?
I think I had this problem twice and both times it was right after adding injector cleaner to an almost empty fuel tank before topping off the fuel. In my case, the gauge wouldn't move up immediately. It would move to the normal level only after hours of driving. Once set, everything works fine later on. But that was not normal.
I suspected the injector cleaner so the next time I added fuel injector cleaner, I made sure to fill the fuel tank at least to half the tank capacity before adding the fuel injector cleaner and then topping off. With this method, everything worked fine and I've never experienced the problem again since.
Maybe your fuel system is dirty and needs cleaning. What about using fuel cleaner for some time and see what happens?
03-07-2017, 04:46 AM
#4
On the other hand, I'd like to know how you got there. I need to change one of my fuel lines because I broke the tabs of one of them at the fuel filter level and I am not sure how to proceed. I can see in the pictures you shared that you had access to the fuel lines. How difficult is it to get there and how easy of access are the lines. If I pull it out, will I be able to reinstall it easily? The one I have to change is the one with the black tabs, the one on the right of the first picture you posted. The fuel line with the blue tab is fine.
Here is what I did: https://www.audiworld.com/forums/a6-...moval-2895182/
Here is what I did: https://www.audiworld.com/forums/a6-...moval-2895182/
03-07-2017, 10:50 AM
#5
AudiWorld Member
Thread Starter
After taking the fuel pump basket out and taking the float apart, I don't see how injector cleaner could cause the float to not read or fix it when it's not reading (I came across a few of those stories on the interwebs when I was searching). The float is a plastic arm with a little magnetic thing at the end. The magnetic thing rides along the resistance sensor. The resistance sensor is sealed. It is the bottom picture of the rectangular thing that says Siemens VDO on it. The black arc is where the magnetic thing moves in an arc.
As far as the lines. To get to where the pictures are you need to:
- Remove rear seat. Pull up sharply on the front edge on driver and passenger side. There are plastic clips underneath and they will most likely break when you pop the front edge off. They are designed to break and cheap from the dealer or online.
- Once the front edge is free, lift up and push towards the back. there is a catch on the back that you need to get past. Keep pushing and pulling up the back until it comes free. Unhook any wiring clips and the seat will come out.
- Lastly, there is a cover on both sides held on by 3 phillips head screws. Once those are out you have access to the fuel pump area.
I didn't really look to see how the lines make their way from the fuel pump area underneath to the fuel pump. They are rigid lines, so I would assume the snake in there somehow. There might also be a cover underneath that can be removed to get access.
I ordered a new float. Once I get that and replace it, I will look a little more to see how those lines are routed.
As far as the lines. To get to where the pictures are you need to:
- Remove rear seat. Pull up sharply on the front edge on driver and passenger side. There are plastic clips underneath and they will most likely break when you pop the front edge off. They are designed to break and cheap from the dealer or online.
- Once the front edge is free, lift up and push towards the back. there is a catch on the back that you need to get past. Keep pushing and pulling up the back until it comes free. Unhook any wiring clips and the seat will come out.
- Lastly, there is a cover on both sides held on by 3 phillips head screws. Once those are out you have access to the fuel pump area.
I didn't really look to see how the lines make their way from the fuel pump area underneath to the fuel pump. They are rigid lines, so I would assume the snake in there somehow. There might also be a cover underneath that can be removed to get access.
I ordered a new float. Once I get that and replace it, I will look a little more to see how those lines are routed.
03-07-2017, 10:59 PM
#6
After taking the fuel pump basket out and taking the float apart, I don't see how injector cleaner could cause the float to not read or fix it when it's not reading (I came across a few of those stories on the interwebs when I was searching). The float is a plastic arm with a little magnetic thing at the end. The magnetic thing rides along the resistance sensor. The resistance sensor is sealed. It is the bottom picture of the rectangular thing that says Siemens VDO on it. The black arc is where the magnetic thing moves in an arc.
As far as the lines. To get to where the pictures are you need to:
- Remove rear seat. Pull up sharply on the front edge on driver and passenger side. There are plastic clips underneath and they will most likely break when you pop the front edge off. They are designed to break and cheap from the dealer or online.
- Once the front edge is free, lift up and push towards the back. there is a catch on the back that you need to get past. Keep pushing and pulling up the back until it comes free. Unhook any wiring clips and the seat will come out.
- Lastly, there is a cover on both sides held on by 3 phillips head screws. Once those are out you have access to the fuel pump area.
I didn't really look to see how the lines make their way from the fuel pump area underneath to the fuel pump. They are rigid lines, so I would assume the snake in there somehow. There might also be a cover underneath that can be removed to get access.
I ordered a new float. Once I get that and replace it, I will look a little more to see how those lines are routed.
As far as the lines. To get to where the pictures are you need to:
- Remove rear seat. Pull up sharply on the front edge on driver and passenger side. There are plastic clips underneath and they will most likely break when you pop the front edge off. They are designed to break and cheap from the dealer or online.
- Once the front edge is free, lift up and push towards the back. there is a catch on the back that you need to get past. Keep pushing and pulling up the back until it comes free. Unhook any wiring clips and the seat will come out.
- Lastly, there is a cover on both sides held on by 3 phillips head screws. Once those are out you have access to the fuel pump area.
I didn't really look to see how the lines make their way from the fuel pump area underneath to the fuel pump. They are rigid lines, so I would assume the snake in there somehow. There might also be a cover underneath that can be removed to get access.
I ordered a new float. Once I get that and replace it, I will look a little more to see how those lines are routed.
03-10-2017, 05:29 PM
#7
AudiWorld Member
Thread Starter
Got the float yesterday. Pulled everything apart again to replace it and could not get the small fuel line connector off this time. The larger line ( not that much larger) came of very easily both times. This other line gave me some problems both times but came off eventually with some pulling. Fought with it yesterday for 30 minutes and today for 45 minutes and I cannot get it off. Went searching for a tool to push the little clips in and get a better grip but couldn't find one today. Going to stop at HF tomorrow and try these (3 Piece Long Reach Hose Grip Pliers).
The picture is from the used assembly I got from ebay. I got it just for the float. It's one of those connectors that you push down on, push the tabs in to release the lock on the ridge and then pull up. Of course it's been near 70 the last 2 times I took it off. Today it was snowing. Maybe the cold weather is making it difficult. Will see if I can steal a hair dryer from someone in the house and try again.
The picture is from the used assembly I got from ebay. I got it just for the float. It's one of those connectors that you push down on, push the tabs in to release the lock on the ridge and then pull up. Of course it's been near 70 the last 2 times I took it off. Today it was snowing. Maybe the cold weather is making it difficult. Will see if I can steal a hair dryer from someone in the house and try again.
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03-11-2017, 07:29 PM
#8
AudiWorld Member
Thread Starter
Finally got the other stupid fuel line off today. The harbor freight hose clamp pliers should have worked but they didn't. I ended up using a curved pick-like screwdriver to wedge the little clip out and then used a paint can lid opener to wedge under the connector (read about that on the interwebs 
).
Got the float replaced so hopefully that was the problem. I didn't get to fill up or go for a drive to see what kind of resistance readings I'm getting on VCDS yet.
It was really cold today so I didn't really look underneath to see how to replace the line that kesiko was asking about. I did do some research since I was afraid I was going to break the clip. From research on the interwebs, it looks like the method is to tie a string to one end of the line and then disconnect it and pull it through. Then tie the new one to the string and pull it back through the opposite way. Hopefully I don't ever have to do that.
Also looks like it's doable to just get connectors and nylon fuel line vs. getting the audi part. Hope I never have to do that project.
).Got the float replaced so hopefully that was the problem. I didn't get to fill up or go for a drive to see what kind of resistance readings I'm getting on VCDS yet.
It was really cold today so I didn't really look underneath to see how to replace the line that kesiko was asking about. I did do some research since I was afraid I was going to break the clip. From research on the interwebs, it looks like the method is to tie a string to one end of the line and then disconnect it and pull it through. Then tie the new one to the string and pull it back through the opposite way. Hopefully I don't ever have to do that.
Also looks like it's doable to just get connectors and nylon fuel line vs. getting the audi part. Hope I never have to do that project.
03-13-2017, 12:08 AM
#9
Finally got the other stupid fuel line off today. The harbor freight hose clamp pliers should have worked but they didn't. I ended up using a curved pick-like screwdriver to wedge the little clip out and then used a paint can lid opener to wedge under the connector (read about that on the interwebs ).
Got the float replaced so hopefully that was the problem. I didn't get to fill up or go for a drive to see what kind of resistance readings I'm getting on VCDS yet.
It was really cold today so I didn't really look underneath to see how to replace the line that kesiko was asking about. I did do some research since I was afraid I was going to break the clip. From research on the interwebs, it looks like the method is to tie a string to one end of the line and then disconnect it and pull it through. Then tie the new one to the string and pull it back through the opposite way. Hopefully I don't ever have to do that.
Also looks like it's doable to just get connectors and nylon fuel line vs. getting the audi part. Hope I never have to do that project.
).Got the float replaced so hopefully that was the problem. I didn't get to fill up or go for a drive to see what kind of resistance readings I'm getting on VCDS yet.
It was really cold today so I didn't really look underneath to see how to replace the line that kesiko was asking about. I did do some research since I was afraid I was going to break the clip. From research on the interwebs, it looks like the method is to tie a string to one end of the line and then disconnect it and pull it through. Then tie the new one to the string and pull it back through the opposite way. Hopefully I don't ever have to do that.
Also looks like it's doable to just get connectors and nylon fuel line vs. getting the audi part. Hope I never have to do that project.
03-20-2017, 06:19 AM
#10
AudiWorld Member
Thread Starter
Turns out replacing that float did not solve my problem. It seems to read correctly for awhile but when I stop or go around a corner, the needle goes up and does not come down. When I have my VAGCOM cable connected and reading the resistance, I see the resistance steady and then swings up and does not come down.
Once I burn some more gas, I'm going to try disconnecting the float on the drivers side. It seems like it adds the resistance from the two floats and it seems like one of them is sticking. Definitely not fun removing doing this when there is a lot of gas in the tank. Just nerve wracking to see that gauge move all over the place.
To repeat, the VCDS gauge cluster test works perfectly. All needles go to the middle as they are supposed to. If it is not one of the floats, then I have no idea what it would be. Can't think of anything that would make the resistance go up and not come down besides the float sticking. Also need to recheck the passenger side and make sure the float isn't getting hung up on anything when it floats up.
Once I burn some more gas, I'm going to try disconnecting the float on the drivers side. It seems like it adds the resistance from the two floats and it seems like one of them is sticking. Definitely not fun removing doing this when there is a lot of gas in the tank. Just nerve wracking to see that gauge move all over the place.
To repeat, the VCDS gauge cluster test works perfectly. All needles go to the middle as they are supposed to. If it is not one of the floats, then I have no idea what it would be. Can't think of anything that would make the resistance go up and not come down besides the float sticking. Also need to recheck the passenger side and make sure the float isn't getting hung up on anything when it floats up.
