Fuel Level Sensor

[bmwstephen]

Even after filling my car to full tank, the gauge is reading about 3 gallons short from full which leads me to suspect is one of the two sensors behind the rear seat. Does anyone know which one it would be given this behavior?

[shogun]

https://www.bimmerforums.com/forum/s...l+level+sensor
https://www.bimmerforums.com/forum/s...l+level+sensor
https://www.bimmerforums.com/forum/s...l+level+sensor

[bmwstephen]

I actually searched and went through those before posting. Those all appear to be related to fuel reading levels that are on empty or half. Mine has been consistantly near full but has never gotten back to the full mark. My solution seemed unique.

[jclausen]

On some BMW's you can do a sweep test on the cluster if you can running that test would tell you if the gauge goes up to full if it did then you would look next at the two fuel level sensors you would have to remove them and test them with an multi meter by moving the float up and down, one side is just a sensor and the other side is the fuel pump and sensor. I don't think I've ever seen a bad fuel gauge

[shogun]

@bmwstephen
did you ever fix that problem and how?

I found this info:

Model: BMW E36 (3 series) including BMW 318ti produced from January 1995
Complaint: Due to the formation of a non-conducting deposit on the conductor surface of the fuel level sensor, the fuel gauge does not read full after re-fuelling, or the fuel gauge is erratic.
Remedy: Remove and replace both fuel level sensors with “Gold system” sensors.

Fuel Gauge Stays Empty after Refuelling/Fuel Gauge Erratic Model:BMW Z3 Roadster/coupe, BMW M roadster/coupe (E36/7). Vehicles produced before December 15 2000
Complaint:After refuelling the fuel gauge will stay on empty or the fuel gauge is erratic. This is caused by a non-conducting deposit being formed on the conductor surface of the fuel level sensor. For the Z3 from September 1998 and the M roadster/coupe FC 2 (Fuel sensor voltage plausibility) will be set in the Instrument Cluster.
Remedy: Remove and replace the fuel level sensor with a ‘Gold system’ sensor referring to repair instructions 16 12 000.
Model: BMW Z3 (E36/7) produced from September 1998 to April 1999
Complaint: After refuelling the fuel gauge reads ¼ full, and will then move extremely slowly to read full. This is due to a software error in the Instrument Cluster.
Remedy: Re-code the instrument cluster using DIS CD Version 18.0 or later:
-Select Coding/Programming/ZCS Coding/E36/Recoding/Kombi and then follow the on-screen instructions to complete the coding process.
-Recoding the instrument cluster will start an internal day counter. If the test3.1 contains a value greater than 0 indicates the instrument cluster will already contain the fix.
--------------------------------
Group 62: Instructions Bulletin Number: 62 12 91 (3421) Woodcliff Lake, NJ June 1992 Subject: Fuel Gauge Displays Inaccurate Fuel Tank Level Models: 3 Series (E36)
Situation: Two separate, but related complaints may be encountered:
The fuel gauge displays an incorrect level; for example, the gauge appears to stick at approximately 1/2.
The fuel gauge does not show maximum level when the tank is filled.

Causes: Two causes may exist for these complaints:
Left-hand side fuel level sender (P/N 16141180517) sticking (causes gauge to appear to stick at approximately ½).
Pump nozzle shuts off prematurely when filling fuel tank, creating the incorrect impression that the fuel tank is full, and the fuel gauge does not show the maximum level.

Correction: E36 vehicles produced exhibiting complaint "A" as described above should have an improved left-hand side fuel level sender (P/N 16141180517) installed. The improved fuel level sender bears a blue date code stamp of "9.91" or later.
Any vehicle exhibiting complaint "A" should be checked for proper alignment of the fuel level senders (refer to sections 16/12-3 and 16/12-4 of the repair manual).
E36 vehicles exhibiting complaint "B" as described above should have the breather line inspected for restriction and position. Refer to Service Information Bulletin 16 01 92 (3553) for this procedure.

[bmwstephen]

No I haven’t did you run into the same issue?

[shogun]

yes, same problem, filled the tank full, the gauge showed first only 1/4 and then very slowly climbed up to 3/4 full after driving abt. 10 miles. Made a cluster test, fuel gauge worked as it should to full. Then I switched ignition on again and the gauge showed again only 3/4 full. Might have to drive more/longer that is goes up to full, didn't drive the past months a lot and the fuel tank was only 1/4 full, otherwise I might have to clean the contact surface of the sweeper on the fuel level sending units, as I did years ago and helped.

[bmwstephen]

My mechanic said it is likely the fuel level sending unit on the rear passenger side (or if there is a leak in the elbow going into the fuel tank within the rear passenger wheelwell). That is the side that would dictate the 1st half of the tank.

Unfortunately the level sending unit was like $600+ last time I checked. He told me it was only worth to change out if it failed completely.

yes, same problem, filled the tank full, the gauge showed first only 1/4 and then very slowly climbed up to 3/4 full after driving abt. 10 miles. Made a cluster test, fuel gauge worked as it should to full. Then I switched ignition on again and the gauge showed again only 3/4 full. Might have to drive more/longer that is goes up to full, didn't drive the past months a lot and the fuel tank was only 1/4 full, otherwise I might have to clean the contact surface of the sweeper on the fuel level sending units, as I did years ago and helped.

[shogun]

$600+ ?
For my 02/98 M3
BMW Fuel Tank Sending Unit - VDO 16146758255 $115 fcpeuro
Continental Fuel Tank Sender (For Gas Gauge); Left Side of Tank | 16146758255 $90.99 Autohausaz
original made by RUNNING LOOS

delivery unit right 16146758736 EKP-VDO MSRP $713.48
VDO fcpeuro $219
URO ~ $120
Continental ~$230 autohausaz

[bmwstephen]

probably looked at the genuine BMW unit. definitely cheaper with VDO but it should be the one on the right side of the tank. If the one on the Left side (driver) went out, then your fuel gauge would be stuck at Empty.

Just a tip when changing either of it out, run the tank to near empty, keep the windows down, and use plastic/trash bags around the area. The way the tank is sitting it can flow out when near full and the gas smell is very strong.

Keep me posted if you ever end up doing this and the results.

$600+ ?
For my 02/98 M3
BMW Fuel Tank Sending Unit - VDO 16146758255 $115 fcpeuro
Continental Fuel Tank Sender (For Gas Gauge); Left Side of Tank | 16146758255 $90.99 Autohausaz
original made by RUNNING LOOS

delivery unit right 16146758736 EKP-VDO MSRP $713.48
VDO fcpeuro $219
URO ~ $120
Continental ~$230 autohausaz

[Veleno]

probably looked at the genuine BMW unit. definitely cheaper with VDO but it should be the one on the right side of the tank. If the one on the Left side (driver) went out, then your fuel gauge would be stuck at Empty.

My car had an incorrect fuel pump installed before I purchased it which had an extra OPEN nipple on it. When I went to fill up at the station gas was leaking out from under the car/tank. I freaked out and thought it might be a leaking/rusted tank. Luckily I live right across the gas station so I drove home praying the car doesn't explode with me in it. Anyhow after I researched more I found the tank is fg and the gas was leaking from the open nipple on the pump (passenger's side). I ordered a continental pump and install was fairly simple aside from locking/sealing ring on the pump to the tank. When I turned the ignition to start, the fuel gauge showed a full tank of gas but I had some seepage from the locking ring so I had to retighten it. On the next turn to start, the gauge showed empty. I thought maybe the sending unit was stuck or blocked so I had to unlock/lock the ring a couple of times until fuel didn't leak out anymore but every time the gauge still read empty. Fast forward maybe 6-8 months (I haven't driven the car) I go to start the car and the gauge is now working and showing a full tank of gas.

My point is that I always thought it was the fuel pumps sending unit (passenger's side) that indicated whether the talk is full or empty. I never considered the driver's side until you made your comment above.
Do you know what the sending unit on the pump (passenger's side) is for then? Maybe both work in tandem?

[bmwstephen]

My car had an incorrect fuel pump installed before I purchased it which had an extra OPEN nipple on it. When I went to fill up at the station gas was leaking out from under the car/tank. I freaked out and thought it might be a leaking/rusted tank. Luckily I live right across the gas station so I drove home praying the car doesn't explode with me in it. Anyhow after I researched more I found the tank is fg and the gas was leaking from the open nipple on the pump (passenger's side). I ordered a continental pump and install was fairly simple aside from locking/sealing ring on the pump to the tank. When I turned the ignition to start, the fuel gauge showed a full tank of gas but I had some seepage from the locking ring so I had to retighten it. On the next turn to start, the gauge showed empty. I thought maybe the sending unit was stuck or blocked so I had to unlock/lock the ring a couple of times until fuel didn't leak out anymore but every time the gauge still read empty. Fast forward maybe 6-8 months (I haven't driven the car) I go to start the car and the gauge is now working and showing a full tank of gas.

My point is that I always thought it was the fuel pumps sending unit (passenger's side) that indicated whether the talk is full or empty. I never considered the driver's side until you made your comment above.
Do you know what the sending unit on the pump (passenger's side) is for then? Maybe both work in tandem?

Short answer is that both serves as level sensors and work in Tandem. But only the driver side is actually a pump.

Long answer: the rear passenger side is not a pump because that side of the tank is naturally draining into the fuel lines where the fuel injectors/vacuum does the rest of the work. Therefore the unit on the rear passenger side is just a fuel level sensor (part number: 51712491567) for reading the Empty to Half Way point on the fuel gauge. It is also why the passenger unit is also is cheaper than the driver side.

Driver side has to function as a level sensor and pump to move the gas to the other side of the tank because of the way the tank is shaped (it has to overcome a bridge). Therefore, it is also responsible for reading the Half Way to Full reading on the fuel gauge. That said, the driver side is likely to wear out faster because it has dual function as a pump as well.

[shogun]

self-healing again. started the engine this morning in the garage, fuel tank showed 3/4, drove it out of the garage, switched engine of (key still in ignition), switched ignition key to position II, gauge then showed empty, fuel tank warning light on. Ignition key off again, removed the key, again in, ignition on and gauge showed full as it should. Then drove around town for shopping, had to park the car several times, now the fuel gauge works always as it should. Have no idea why it suddenly works again. Same happened years ago after filling the fuel tank and procedure above solved the problem, a bit driving, engine off, key off, engine on etc.
Cluster test works perfect, the fuel gauge needle goes from empty to full during the test.

Edit: cluster test added with details https://www.bimmerforums.com/forum/s...6-Cluster-test
https://www.youtube.com/watch?v=wFANuPz9Lkw

Edit 2: checked for fault codes in a BMW shop and they got the fault fuel tank breather valve defective. The shop master was of the opinion that this could have caused also a wrong fuel gauge opinion.
Changed the breather valve 13901748875 against another good one, no more fault code.

[bmwstephen]

It just sounds like the leveler might be gumming up here and there. whats this cluster test you speak of? I think I might need to try that.

Edit: wow just ran the test and mind blown. Turns out it is my cluster because when it tested, the fuel gauage did not go to the full end and stopped short of it. Maybe it needs to be rebuilt or calibrated.

If that is the case good timing because I have cluster dark spots anyway so be worth Brett's services

[Veleno]

Short answer is that both serves as level sensors and work in Tandem. But only the driver side is actually a pump.

Long answer: the rear passenger side is not a pump because that side of the tank is naturally draining into the fuel lines where the fuel injectors/vacuum does the rest of the work. Therefore the unit on the rear passenger side is just a fuel level sensor (part number: 51712491567) for reading the Empty to Half Way point on the fuel gauge. It is also why the passenger unit is also is cheaper than the driver side.

Driver side has to function as a level sensor and pump to move the gas to the other side of the tank because of the way the tank is shaped (it has to overcome a bridge). Therefore, it is also responsible for reading the Half Way to Full reading on the fuel gauge. That said, the driver side is likely to wear out faster because it has dual function as a pump as well.

Thanks for clarifying!

self-healing again. started the engine this morning in the garage, fuel tank showed 3/4, drove it out of the garage, switched engine of (key still in ignition), switched ignition key to position II, gauge then showed empty, fuel tank warning light on. Ignition key off again, removed the key, again in, ignition on and gauge showed full as it should. Then drove around town for shopping, had to park the car several times, now the fuel gauge works always as it should. Have no idea why it suddenly works again. Same happened years ago after filling the fuel tank and procedure above solved the problem, a bit driving, engine off, key off, engine on etc.
Cluster test works perfect, the fuel gauge needle goes from empty to full during the test.

Edit: cluster test added with details https://www.bimmerforums.com/forum/s...6-Cluster-test
https://www.youtube.com/watch?v=wFANuPz9Lkw

I love a car that heals/fixes itself! lol

It just sounds like the leveler might be gumming up here and there. whats this cluster test you speak of? I think I might need to try that.

Edit: wow just ran the test and mind blown. Turns out it is my cluster because when it tested, the fuel gauage did not go to the full end and stopped short of it. Maybe it needs to be rebuilt or calibrated.

If that is the case good timing because I have cluster dark spots anyway so be worth Brett's services

I know how you feel. I ran this test when I first picked up the car and just watching it was awesome.

[NeilM]

Short answer is that both serves as level sensors and work in Tandem. But only the driver side is actually a pump.

Long answer: the rear passenger side is not a pump because that side of the tank is naturally draining into the fuel lines where the fuel injectors/vacuum does the rest of the work. Therefore the unit on the rear passenger side is just a fuel level sensor (part number: 51712491567) for reading the Empty to Half Way point on the fuel gauge. It is also why the passenger unit is also is cheaper than the driver side.

Ddriver side has to function as a level sensor and pump to move the gas to the other side of the tank because of the way the tank is shaped (it has to overcome a bridge). Therefore, it is also responsible for reading the Half Way to Full reading on the fuel gauge. That said, the driver side is likely to wear out faster because it has dual function as a pump as well.

That's not how the fuel level senders work.

Each level sender is functionally identical, and reads its own side from 10±2 ohms (all the way empty) to 250±5 ohms (completely full). There is no top or bottom half measurement. The two senders are wired in series, so no matter how the fuel contents may be distributed between the two tank halves at any instantaneous point in time, the combined fuel level reading won't change. However the series connection also means that a fuel level reading anomaly won't tell you which sender is at fault. For instance if one sender fails open circuit, then the fuel level will always read as zero but you won't know which sender is faulty. (Of course a zero reading could be due to something other than a failed sender, e.g. a broken wire, loose connector, etc.)

The senders consist essentially of an open potentiometer. There's a resistor track with a wiper arm that's moved by a fuel level float on an arm, such that a different electrical resistance is read as the float raises and lowers. Eventually the resistor track may get dirty, corroded or just plain worn out, leading to inconsistent or incorrect readings. The senders can be individually tested without opening up the tank by pulling both metal tank access covers under the rear seat base, detaching the revealed electrical connectors on both sides, then taking resistance measurements across the pins on the top of each sender assembly.

Neil
96 M3

[shogun]

found some additional info here in the driver Info system training paper https://www.rfdm.com/Daniel/MRoadste...1driverino.pdf

see page 8 8 driver info system​

Fuel gauge: 2 lever type floats wired in SERIES provide the input for the fuel gauge display. When the fuel reserve threshold is reached , the low fuel warning LED is iluminated.



page 14 also shows data for cluster test Nr. 06

fuel gauge.......................hex value , display of hexadecimal codes in relation to gauge position
A (empty)..........................0d
end of reserve....................37
B......................................54
C......................................5c
D center............................4f-23
E......................................1e


Test 14 software reset: the reset must be carried out if any faults are present that are not plausible before any components are replaced. After the reset, the system will exit the TEST mode and the lock will be reactivated.