Fuel sender resistance readings, guage faulty

[SkodaSuperb12]

Skoda Superb 2012 2.0 tdi

Anyone got any info on what the fuel sender resistance readings at reserve & full should be ?

 

My fuel guage only reads 3/4 full when brimmed and it then shows empty / fuel light on when clearly there is lots of fuel left

 

Thought I would start by checking Ohms readings before pulling it all apart

 

Also just out of interest can vagcom or whatever software adjust the fuel guage to suit my resistance readings ? 

 

Thanks 

[KenONeill]

41 minutes ago, SkodaSuperb12 said:

My fuel guage only reads 3/4 full when brimmed and it then shows empty / fuel light on when clearly there is lots of fuel left

Firstly, is this an actual or perceived issue? My fuel gauge only reads 7/8 when filled to the pump click and then left overnight for the fuel to come right up to ambient temperature and use some of the expansion space. Never mind what the gauge reads; the low fuel light comes on with about 50 miles available range left.

[J.R.]

Low fuel light comes on half way into the red range which equates to 1/8 on the guage, 1/8 tank capacity if everything correctly calibrated.

 

Below half a tank it falls faster than the real fuel level does and also the mile remaining maxidot display, when it shows empty and zero miles remaining there will be a virtual reserve capacity of between 5 and 7 litres, how many miles depends on the engine and driving style, speed, conditions etc.

 

Using VCDS I can see the resistance of both my fuel level senders (its a saddle tank) how many litres of fuel each are recording and also how many litres total, I can also correct the guage calibration to make it read full scale on a full tank.

 

So to recap, you can trim the fuel guage to read correctly on a full tank, it will tell the truth down to 1/2 a tank  and then become more and more pessimistic as it falls to create the virtual reserve capacity. It might start at less than 1/2 tank capacity, its very difficult to see initially.

Edited 1 January, 2022 by J.R.

[SkodaSuperb12]

Thanks for comments

My guage is well out

With a 60 litre tank I can brim it till I see fuel ,it never goes above 3/4 then after about 250 miles , I hit fuel light

I know from refilling about 25 / 30 litres Istill have lots of fuel left

Car should easily do 400 miles around town 

 

So possibly I could adjust on VCDS ?

 

That's interesting 

[SkodaSuperb12]

Pls could you tell me what VCDS cable / system you use ? What sort of price ? 

 

Ta 

[langers2k]

For a 2012 Superb, you'll need a genuine VCDS micro-CAN, HEX-USB+CAN, HEX-V2 or HEX-NET interface. The cheapest currently available would be a 3-VIN HEX-V2 at ~£225. That being said, it'll help with diagnostics and fault reading but despite J.R.'s comment, I don't think it can 'calibrate' the fuel gauge...

 

Having looked a scan for a similar vehicle, there is an adaption channel named 'Display correction of fuel gauge' but that doesn't seem to do what you'd need: https://forums.ross-tech.com/index.php?threads/28648/#post-242725

 

VAG seemingly haven't implemented that functionality as the fuel senders should all be close enough as not to need it. A quick google suggests that:

- 50 ohms is full

- 160 ohms is half full

- 350 ohms is empty/reserve

 

No idea if that's correct for a Superb but it's the only obvious info I could find

[SkodaSuperb12]

Thanks for resistance readings , I will measure

 

A few youtube searches show vcds has the option to adapt / calibrate fuel guage readings 

 

Ta 

[SkodaSuperb12]

https://youtu.be/evBqjMyqpsY

[nige8021]

With VCDS if you go into controller 17 (Instruments) and the measuring blocks it will give you the resistance value and if you hover your mouse pointer over that block it will give an upper & lower resistance value 

[langers2k]

That video seems to tally in to the rosstech comment, that channel is to adjust the fuel reserve level. Rather than calibrate the sensor through the full range.

[SkodaSuperb12]

Thanks for comments

 

I personally am beginning to think that my fuel guage issue is now either a varying resistance issue either through corroded contact or the float resistor mechanism failing / sticking 

 

Yesterday the fuel guage was on red , today it reads different and more correct at below half tank 

 

I think inspecting the tank will now be necessary as its clearly not just adjustment 

 

Can't wait, not

[J.R.]

8 hours ago, langers2k said:

That video seems to tally in to the rosstech comment, that channel is to adjust the fuel reserve level. Rather than calibrate the sensor through the full range.

Watching the video the measured resistance of the sender remains the same but it changes the quantity of fuel displayed and I am guessing also the miles remaining on the display.

 

The question is does it change the quantity displayed on a full tank?

 

I am going to do some testing, I would really like for the first time ever to drive a Skoda that tells the truth at 1/4 tank and below but not if it compromises the guage above say 3/4 of  a tank.

 

My gut feeling is the algorithm will remain the same, true reading and miles remaining down to half a tank (or a bit lower) then gradually fiddling the readout to create a virtual reserve capacity.

 

When my guage has dropped to 1/2 level and I have driven 300 miles its reasonable to expect with the same driving conditions another 300 miles of range, or to put it another way, if after filling the tank it shows 600 miles of range and 300 when the guage shows half full it should not be showing empty and zero miles remaining after another 230 miles.

[SkodaSuperb12]

Yep

Currently I fill up and use the trip as a guide to how much range / fuel I have left 

[SkodaSuperb12]

Just a follow up to this issue 

When tank was fairly low on fuel i accessed the fuel pump and float sender in the tank

I exercised the gloat sender back and forwards with my hand 

Put it all back together and so far guage is now reading correct

 

Filled the car up and so far the needle now shows full correctly

 

So looks like the issue is a dodgy in tank sender 

Will see how I get on now