Hello,

Can anyone give me a work through to check the fuel gauge on a FII?

My daughter broke down in the fast lane on the M25 - I have not seen the car yet.

Apparently the fuel gauge showed FULL and there was no fill up indicator when she broke down.

It all went well with no crash, but when the breakdown service picked her up he went for fuel supply problem, tapped the dash panel and the needle just dropped..... After putting in some of his supply the car ran just fine. My daughter filled up but the gauge did not show this and the range is pretty minimal. So she is going by the trip range now.

We did replace the BCM recently with a used one for the wretched windscreen wiper failure. I had a look at the pin outs on the J519 but could not see any for the fuel gauge.

The fuel gauge sender unit from the tank links straight to the dash panel.

It also looks as if the sender unit can be replaced without having to by the complete tank insert with pump.

Maybe check that theres voltage going to fuel sender. Think it should be 5-6v. If theres voltage there then it may well be the sender. Not sure but on my old cars if the supply to sender was earthed it should make guage read full. If theres voltage there and when earthing no guage movement it could be the guage or a cluster fault. Do not check with sender removed if its petrol. Sparks and petrol are never a good idea. Check the wiring as well for damage as if its shorted somewhere it may show full all the time.

Alasdair

If your cluster shows outside temperature somehow, see if that is working.

I faintly remember that the supply within the cluster that feeds that NTC sensor is shared with the fuel gauge supply.

So if something was pulling that down - like water ingress into outside temp sensor/connector - it might affect both functions.

Thanks for the replies.

When the car is back I will use VCDS measuring blocks to check the dash. The next step was to check the connections.

I am pretty sure I saw the temperature display in the dash.

I had a look at the car today.

Strangely the gauge responds now to filling up and using petrol, just in reverse, i.e. it shows empty when the tank is full and vice versa.

With VCDS the fuel gauge moves and responds smoothly.

I removed the fuel pump with the sender. Everything reeks of petrol.... and it was a pain to get the 4-pin connector off the pump.

I measured across the fuel sender - 0.11Ohm. I do not know what it should be.

I removed the sender unit and swapped the 2 connecting wires, hoping that it would reverse the display, no luck. Still full display on empty.

I have ordered a replacement sender unit now.

Just an update.

I replaced the sender last night as I thought that HAS to be the faulty part. I think the fault is not fixed as the fuel display on the gauge was the same as before. Unfortunately I did not do any major testing, i.e. level up and level down and electrical measurements.

I looked on the wiring diagram again thinking I must have missed a connection but there is only one straight connection into the dashboard. I have not removed the dashboard for inspection yet. That will have to wait as we are going away soon.

Any other ideas?

It may be the connector at rear of cluster thats needing cleaned or reseated. My old octavia had weird dash problems with random lights and guages not performing well. I removed cleaned and reseated and it came back to life. Check the cluster for dry solder joints while you have it removed and remember to disconnect battery before removal as imobilser can stick on.

Alasdair

Thanks for the dashboard hint.

The display is still working in reverse. The car is away again and it will be a few weeks before I can check again.

I am still thinking that there is a connection to the BCM fix when there was a short on the circuit board.

I read on here a similar problem. They replaced fuel sender unit and guage worked in reverse. It was mentioned that early and later fuel pump/sender units are different and if the wrong one is used can cause this problem. As you havent replaced sender but relaced BCM I am wondering if the two are linked and its the replacement BCM thats causing problem. Might be worth checking part numbers if you still have old one. May be wrong but worth a check

Alasdair

The fuel gauge is working in reverse with the old and the replacement fuel sender.

I still have the previous BCM and can try that again.

On the wiring diagram the fuel pump / sender do not have a link to the BCM.

Edited 5 March5 Mar by 26DIPP

Had another google and the wiring on newer models I think goes to bcm but on older seems to go direct to cluster as in yours. It may be a fault in cluster itself thats causing problem as both old and new work in reverse. As both work in reverse I assume that the wiring is ok but maybe problem at cluster?

This is an update on the reverse display of the fuel gauge.

Today I changed the BCMs - replacement out and an old one I still had but with no functioning wipers in.

I took pictures...

Reverse display

Correct display

As you can see on the clock they are 30 minutes apart.

The BCMs have the exact same PN and nearly the same age. The biggest difference is that the BCM I bought as a replacement for the failed one came from a VW Fox from 2009, so the same year as my daughter's FII.

I need to find some pin outs for a 6Q1937049F BCM for a Fox. I have been checking the FII pin outs and nothing indicated that there is any connection to the fuel gauge. Maybe the FL ones do but they are a complete new design.

I had started to make plans to replace the complete electrics from dashboard, ignition barrel, door lock, keys...

So, the Fox must be using a different wiring with the same PN.

I may have Fox wiring info.

I could swap a wiper relay out for you to revive the original.

Hello Pete,

Thanks for the offer. I have already ordered a replacement BCM off Ebay, this time a Skoda one.

I would be interested in the wiring / pin out of the Fox BCM out of couriosity though.

I do have some info.

Is there a date code on the Fox BCM? There's a different document of info either side of August 2009.

First diagram in the August 2009 onward document seems to show two wires from fuel gauge sender going to cluster and nowhere else.

Edited 30 March30 Mar by Breezy_Pete

Same applies for the last fuel gauge diagram in the previous document, except the earth may not come from the cluster directly in that case.

Bit mystified here.

Hello Pete,

I will take some pictures tomorrow.

Hi,

I will attach some pictures of the VW BCM.

I cannot compare this at present because the old BCM is still in the car until another replacement arrives.