Fuel gauge - random behaviour?

**Mr Zap** · 01-05-2021,08:05 PM

My fuel gauge has started behaving erratically - most of the time showing zero but occasionally showing full (max). It says what it says from start up and doesn't change while driving, and yes there is fuel in it, plenty!
It seems a bit odd for it to be the sender, especially going from empty to full, usually a dudd sender reads one or the other, not both?? I've checked the plug and connections to it, all seems ok. I even tried disconnecting the battery for a while and reconnecting it to see if that reset the system - no luck.
Any ideas?

**Roverfan** · 01-05-2021,09:55 PM

I suppose its time to start to verifying. Verify you have a good power and ground at the fuel pump, verify signal output voltage, verify that voltage is getting to the cluster

**C6Allroad** · 02-05-2021,11:49 AM

Originally Posted by Mr Zap

My fuel gauge has started behaving erratically - most of the time showing zero but occasionally showing full (max). It says what it says from start up and doesn't change while driving, and yes there is fuel in it, plenty!
It seems a bit odd for it to be the sender, especially going from empty to full, usually a dudd sender reads one or the other, not both?? I've checked the plug and connections to it, all seems ok. I even tried disconnecting the battery for a while and reconnecting it to see if that reset the system - no luck.
Any ideas?

You need to give details on your model of car as there are known issues related to specific models.

**Crasher** · 02-05-2021,01:46 PM

Due to the saddle design of the tank, it is a dual sensor system, the gauge can be tested and the sender outputs viewed in measuring blocks.

**Mr Zap** · 02-05-2021,03:29 PM

Ok, well re vehicle details it's a C6 '05 reg Quattro, 3ltr TDI estate 224bhp. Does that help? I've heard they can suffer from dash failures due to dry solder joints?

The fuel gauge has shown zero once or twice before but has always recovered, this time is the first for the zero to max fluctuation and for the past couple of days it's shown zero permanently.

I can't take the car off the road right now to pull the cluster out and have a look so my only option is to keep the tank filled up!!

**C6Allroad** · 02-05-2021,04:12 PM

Originally Posted by Mr Zap

Ok, well re vehicle details it's a C6 '05 reg Quattro, 3ltr TDI estate 224bhp. Does that help? I've heard they can suffer from dash failures due to dry solder joints?

The fuel gauge has shown zero once or twice before but has always recovered, this time is the first for the zero to max fluctuation and for the past couple of days it's shown zero permanently.

I can't take the car off the road right now to pull the cluster out and have a look so my only option is to keep the tank filled up!!

Could well be the common issue on these cars of the wiring failure in the tank sender. Try removing the metal cover under the drivers side rear seat and giving the top of the pump enclosure a good thump or 2 with a heavy blunt object and see if it kicks it into action. Mine does this occasionally but has been OK for the last 9 months.....

**Mr Zap** · 04-05-2021,01:08 PM

OMG ... it worked!! Gentle couple of taps with the battery end of the cordless drill and hey presto! Thanks C6Allroad.

Has anyone figured out why this works, i.e. what's wrong? Is it a stuck float gauge, or wiring issue etc?

**swalker** · 04-05-2021,01:30 PM

there is audi documentation on line and repair kit for it, not sure if it was a recall?

there is a link somewhere to the recall notices, i will see if i can dig something out for you

TSB is what i was looking for not recall..

https://drive.google.com/file/d/1YFI...ew?usp=sharing
https://drive.google.com/file/d/1syD...ew?usp=sharing

**C6Allroad** · 08-05-2021,01:32 PM

Originally Posted by Mr Zap

OMG ... it worked!! Gentle couple of taps with the battery end of the cordless drill and hey presto! Thanks C6Allroad.

Has anyone figured out why this works, i.e. what's wrong? Is it a stuck float gauge, or wiring issue etc?

It's a wiring issue but one way to avoid repeated failure after giving it a thump is to not overfill the tank i.e once the pump stops don't try to squeeze more in.

**Mr Zap** · 08-05-2021,02:02 PM

Sorry to say this but I've since had to thump the tank twice more, and that's without putting any more fuel in, let alone overfilling it.

I've now seen the stuff online about this, including youtube videos and the vastly overpriced repair kit so at some point I guess I'm going to have to pull the thing out and see what's what for myself. I don't like the £190 price tag for a brand new assembly though so I'm wondering if the thing would suffer any ill effects if I just cut the connectors off and solder & heatshrink the wires? They seem to be part of the overall assembly so the chances of ever needing to separate them again are at best pretty minimal.