Fuel tank sender issue?

Ken Long

Ken Long

Member
Odd issue has just manifested itself.
We've driven down to Bournemouth to visit my mum. On arrival fuel gauge was showing between 1/4 and 1/2 (closer to 1/4 probably). Popped out to run an errand, got back in and "beeeeeep" and fuel warning light comes on. Fuel gauge is as low as it's possible to go.
I shot round to Tesco to fill up, and put in 22 litres, so probably was 1/4 of a tank. Warning light is still on the dash, and gauge shows just over 3/4s full. I drive back to mums (about 10 minutes) and the gauge has crept up to full. I switch off and then turn the ignition to on and the warning light is off and usual dis info is displaying.
Any ideas? Is it a sender issue or just a hiccup?
(Our A2 is 1.4 TDI, 51 plate.)
 
One for @timmus I think. Hoping he'll know how the cluster software works in terms of what delaying/averaging of the signal from the sender it might perform, so he can work back from the symptoms as described to point to what might have caused this issue.
 
I’d say it’s most likely to be the in-tank fuel sender sensor that is either dirty or on its way out.
 
I have had this exact issue from time to time in my car which presumably uses the same sender as it is the same age and therefore has the same small diesel tank. I have never got to the bottom of the issue as it it is very intermittent (usually I go months with the gauge working normally). I would like to resolve the issue but it's very hard to diagnose with it happening so infrequently.

While not a solution, I always reset my trip counter when filling my tank and I know roughly how many miles I can get from a tank so always have that as a sort of backup fuel gauge
 
hydo14 said:
While not a solution, I always reset my trip counter when filling my tank and I know roughly how many miles I can get from a tank so always have that as a sort of backup fuel gauge
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I've been doing that, and I reckon I get about 100 miles per quarter tank, so that is a backup!
A2Steve said:
I’d say it’s most likely to be the in-tank fuel sender sensor that is either dirty or on its way out.
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Is that a reasonably straightforward thing to sort?
 
Ken Long said:
I've been doing that, and I reckon I get about 100 miles per quarter tank, so that is a backup!

Is that a reasonably straightforward thing to sort?
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The fuel level sender is easy to replace but I would imagine hard to source a replacement part.

Under the rear drivers passenger seat carpet there’s a cover under the carpet. From this there’s a wire and a plug to disconnect as well as some fuel pipes and then you need to unscrew a big circular ring the level sender should then be able to be lifted out vertically and replaced or if there’s a repair possible to the sender then this is the time to do it.

I expect the job to be very similar to how the fuel pumps in other VW group cars are replaced
 
I had this problem and cleared it by putting some diesel injector cleaner in the fuel and then using Shell premium diesel. I think it cleared up by the end of the second tankful.
 
Just had a look at the workshop manual. You can check the resistance of the sender with a multimeter it should be 96.6 ohms once you get down to 7 litres (I.e the reserve when the light comes on) and then drop to 54 ohms for an empty tank (this is only true for the earlier cars with tge 20 and 34 litre tanks up to 2002)

The measurement is taken across the two pins that are accessible when you remove the connector once the carpet and access hatch is unscrewed under the rear drivers side passenger seat
 
There are 2 voltage regulators fitted to the A2 and am wondering if the issue lies there? Back on older cars voltage regulator would play havoc with the gauges.
 
hydo14 said:
Just had a look at the workshop manual. You can check the resistance of the sender with a multimeter it should be 96.6 ohms once you get down to 7 litres (I.e the reserve when the light comes on) and then drop to 54 ohms for an empty tank (this is only true for the earlier cars with tge 20 and 34 litre tanks up to 2002)

The measurement is taken across the two pins that are accessible when you remove the connector once the carpet and access hatch is unscrewed under the rear drivers side passenger seat
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It is worth noting that the newer cars 05.2002 onwards the resistances work the other way (i.e are high on an empty tank and low on a full tank) but are also higher in magitude
 
Proghound said:
One for @timmus I think. Hoping he'll know how the cluster software works in terms of what delaying/averaging of the signal from the sender it might perform, so he can work back from the symptoms as described to point to what might have caused this issue.
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A2Steve said:
I’d say it’s most likely to be the in-tank fuel sender sensor that is either dirty or on its way out.
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I concur with Steve. Although I have seen dodgy fuel gauge issues due to the instrument cluster, this one sounds like a dirty in-tank level sensor.

Cheers,

Tom
 
Thanks everyone for your diagnoseses. We've just driven home (with a couple of stops) and no repeat of the issue.
How do I go about obtaining an in tank level sensor?
 
Best bet is probably to put a wanted advert on this forum in the marketplace. You will need to make a donation to access it. It could also be very intermittent and something that’s not super urgent to fix
 
hydo14 said:
Best bet is probably to put a wanted advert on this forum in the marketplace. You will need to make a donation to access it. It could also be very intermittent and something that’s not super urgent to fix
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@Ken Long already has Market access 👍

For the record, it's not done by making a donation, but by upgrading your account, here.
 
I would remove the fuel sender as described in this thread (quite easy) and inspect it first. The variable resister slider is exposed and easy to wipe clean if it was very dirty. It might just be that simple.

Trevor
 
As I am having the same issue I may give that a look tonight as I will have a nearly empty tank by the time I get home. Will post photos if I can.
 
No need to worry about how much fuel is in the tank when removing the sender unit. It comes out of the top of the tank.

Before taking it out have a good check of the wiring plug and socket for damage or even just loose and the loom running from there.

Be careful when trying to clean the variable resistor as you do not want to damage it. GENTLY rub it with an old toothbrush dipped in the fuel in the tank. Do not use a cloth.
 
Same issue on one of my TDI's, I'll take a look at the weekend too and get some photos - been meaning to investigate it for ages. The hardest part of the job is undoing the black plastic ring that holds the sender in - i've normally had to use a piece of wood and a hammer to undo it....sometimes lining up to retighten can be a bit of a fiddle too, careful not to cross thread it - easily done in my experience.
 
audifan said:
No need to worry about how much fuel is in the tank when removing the sender unit. It comes out of the top of the tank.

Before taking it out have a good check of the wiring plug and socket for damage or even just loose and the loom running from there.

Be careful when trying to clean the variable resistor as you do not want to damage it. GENTLY rub it with an old toothbrush dipped in the fuel in the tank. Do not use a cloth.
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I have a similar ish issue
Is it ok if you can't find an old toothbrush 🪥 and just use the Mrs,s one .. then give it blooming good rinse and pop it back in the bathroom cabinet 😐
 
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