Fuel gauge fault

[Andrew Lenihan]

Hi, hoping someone can help! I have a Audi 80 Cabriolet and my fuel gauge and temp gauge have an intermittent fault, working then not working.

Is this a common fault and easily rectified? Thanks for any assistance, Andy.

[Magnet]

Hello Andrew,

This might (only just might) be fitted with the much earlier voltage stabiliser which damps the needle movements. If it is, then the symptoms you quote were not untypical of a problem with these small replaceable units which were usually fitted on or near the fuel gauge. 

Of course, I could be completely wrong and the gauges are the later electronic ones, but worth an investigation of the wiring diagram. 

Also I would not ignore the possibility of a fuse related issues with intermittent faults. It is often assumed that since the fuse is intact that the circuit is fine, but it is not uncommon to find corrosion around in the fuse contact area, and it’s well worth spraying the fuses with contact cleaner while wiggling the actual fuses - be careful to keep on contact spray away from paintwork. 

Kind regards,

Gareth. 

[Andrew Lenihan]

Thanks Gareth, I will give it a try, problem I've got is I can't find which fuse it is and where?

[Andrew Lenihan]

Hi Gareth, I've traced the sender unit and found I have got 6.5v there, I presume that should be 12v, any ideas?

Thanks Andy.

[Magnet]

Hello Andy,

Where are you connecting the earth (-ve) prod of the meter to? Are you sure it’s a good earth? If yes, I take it you are taking the reading with the terminal disconnected from the sender .

Kind regards,

Gareth.

[Andrew Lenihan]

Thanks for your help Gareth, I put my meter on to the sender plug connection and to earth on the rear shocker head bolt, all I could get was 6.5 volts?

I was expecting 12v. Do you know were this pair run to from the sender unit, ie, fuse or gauge?

Were off to the south of France in a fortnight and I would like to know how much fuel I have. This has only just started happening.

Thanks again for your help. Andy.

[Magnet]

Hello Andy,

Apologies for appearing to be asking more questions and double checking. 

When you are connecting your meter to the plug connection, can we take it you actually have the plug disconnected from the sender and are are putting the prod of your meter into the disconnected end of the cable that would fit onto the sender unit? 

Also, could you run a length of wire directly back to the battery earth terminal rather than depend on a separate earthing point for your meter. All a bit pedantic, but need to be clear.

Have you managed to find a wiring diagram yet? 

Kind regards,

Gareth. 

p.s. 

I have a fuel gauge on a MG TF which is reluctant to read over 1/2 full even when full, and I’m really not confident on its ability to read empty when it is! We are off to Brittany in a few weeks, so it’s goung to be regular top ups to ensure it’s full! 

[Andrew Lenihan]

Hi Gareth, yes disconnected from the sender and tested the positive in the plug, haven't tried an earth direct but will do but I would have thought the body would be earthed.

Were off to the south of France on the 19th, can't wait! Thanks for your help. Andy.

 

[Magnet]

Thanks Andy,

If you are indeed picking up a good earth, then it looks like you may have a voltage stabiliser type set up feeding into these gauges, and this could be giving you your intermittent fault. You will need to find a wiring diagram and check. 

Enjoy the trip.

Kind regards,

Gareth.

[curly1701]

On 5/25/2019 at 9:30 PM, Andrew Lenihan said:

Hi, hoping someone can help! I have a Audi 80 Cabriolet and my fuel gauge and temp gauge have an intermittent fault, working then not working.

Is this a common fault and easily rectified? Thanks for any assistance, Andy.

Hi Andy, I’m new to this forum & writing in forums.

did you sort your fuel & temperature sender gauge fault. I have just bought a 1994 Audi 80 Cabriolet & I have a similar problem.

How did you fix the problem 

 

[Magnet]

Hello Colin, 

Andrew hasn’t returned to the forum for over 3 years. Probably best to send him a message via. the forum. 
Kind regards,

Gareth. 

[IHK 11]

Hi Colin im no expert but i had a problem with my temp gauge being tempremental and then not working at all. If its a wiring issue then it will either be at the instrument cluster or the coolant temp sender. If you havent removed the instrument cluster then its more likely to be at the temp sender. The wiring can be very thin and brittle going into the sender especially as the cars are quite old now. Its also an area with a lot of heat around aswell. I fitted a new temp sender to my Audi 80 coupe and i managed to weaken one of the wires going into the sender as i put everything back. My temp gauge was always slow moving and stayed low and then stopped working altogether. Once i repaired the wiring the temp gauge has been ok ever since. Its possible it might be something at the instrument cluster tho seeing as its a temp gauge and a fuel gauge. I had a similar problem on a Bmw e36 where the fuel and temp gauge would work fine then totally drop to empty and cold and this ended up being a fuse that just wasnt in fully. I dont know if this is any help to you but i hope you manage to sort it out. Good luck from Ian!

[curly1701]

Thanks Ian, I appreciate the advice 👍

[IHK 11]

No problem 👍