Car wound not start when fuel tank go below half a tank

Car wound not start when fuel tank go below half a tank!. I had this problem since I got the car from second hand, Audi A2 Tdi 1.4 2001 car only use top half of the tank once it goes below half a tank its struggle to start(almost look like losing fuel pressure on fuel line)once refuel and crank many times its start up. I used the car for 60K miles with no problem (fuel pump works fine once re fill fuels to top )
Any idea what casing this?


Active Member
While I cant give any direct answer a few questions may help others diagnose:

How many liters of fuel do you put back into it when you fill back up? Reason for asking is it may be that the fuel level sender is faulty and at least if we know how much is being put in can identify if this could be an issue? Does this happen when car is both hot and cold? Does it run well up to the point you switch off then start again or does it shut off when less than half a tank?

Has it had a fuel filter change? If so when, and was this around when the fault started.

Is there any leaking around the tandem fuel pump on the engine? (situated right side of engine head when looking at it from the front of the car).

Do any fault lights light up? Have you had a diagnostic done?


Dick Chown Award 2016
Could it just be that you have a faulty fuel level sender? I mean that with it showing half a tank, could it actually be empty??

Have you filled it to the brim and seen how many miles you get before the engine cuts out again?

Steve B
Hi Paul, Big thank you for the reply, its take around 12 litres to fill up(from half a tank to top). Its happens in hot and cold(every time), never shuts off normally, only shut off once tank is go below half.
Fuel filter not changes since ii had it(hoping to change it soon), not notice a leak around tandam pump. No lights or diagnostic codes in memory. I have also pulled many hairs trying work this out..
Hi, thank you for the reply, its take around 12 litres to fill up(from half a tank to top). So its can not be faulty sender.. its really starve fuel at half at tank.


Technical Specialist 1.2 TDI
not notice a leak around tandam pump
If the leak is on the suction (inlet) side of the pump, you won't notice any leak because any leak will be air being sucked into the system, rather than fuel from the tank. I had this problem a few months ago, but it wasn't related to fuel level. A pump rebuild cured the problem.



Well-Known Member
Recommend you give priority to changing the fuel filter. (It could be the straw that's breaking the camel's back)

As there is no electric pump in the fuel tank, system priming and fuel delivery is down to the tandem pump on the engine. At cranking speeds, any restriction to fuel flow may prevent the engine starting, especially if the tandem pump is worn.
It's possible the higher the fuel level in the tank, which gives a small positive pressure effect, is just enough to overcome any resistance to fuel flow at low revs

Cheers Spike
When I first read this I immediately thought it has to be a fuel pump problem of some sort, but I wasn't sure what so I decided to wait and see what others thought. I still think that and I'm still unsure why, but I presume it is either to do with the pickup point on the fuel pump, e.g. the lowest point must be blocked in some way, or something to do with the fuel level dropping below the level of the fuel return pipe, some sort of suction/siphon issue if the pump is weak.

However, there is a third possibility and that is that as it's been like this since you bought it, whoever had it before had the fuel pump out and the pipes have been mixed up in some way. And something else that has just occured to me, is the fuel cap vent blocked causing a vacuum in the tank after about 1/4 of the tank used?


Well-Known Member
From the 1st and 4th post it reads like the fuel filter has not been changed in 60k miles, and depending on the previous owners service routine,possibly a lot more.

If that's the case, I'd also expect it to be a bit down on power. The filler cap theory is easy to check. Just remove it temporarily before starting.

The question about an electric fuel pump in the tank has come up many times but for me this thread confirms there isn't one -

Cheers Spike


A2OC Donor
Hi spike, thank you for the reply, I was under impression that 2001 - 1.4 Diesel TDi use “electric fuel pump build in side the tank,
There is an error in the A2 documentation that says the TDI has a fuel pump in the fuel tank. The petrol A2s have such a pump, but the TDIs do not.

My first line of attack with this problem would be to change the fuel filter. It's so frequently overlooked by garages when performing a service.

It's also possible that your fuel tank has been contaminated by 'diesel bug':
This sludge floats around in the tank and can block pipes and filters. It may be that a culture of microbes is floating in the tank, causing a blockage when half the tank has been used.


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Definitely no pump in the tank. I've been in mine 3 times to change the sender. Two senders from breakers and one OEM and I still don't trust the gauge. Carry around 5ltrs of diesel.
Thank you all for valuable input and support, I have summand courage and open the fuel tank and got the sender unit out. Bottom whole was block from gunk casing fuel sender fill only from top. Once fuel goes down below the top the fuel sender car could not use the bottom half of the tank.
Disassembled and Cleaned the in tank sender unit (No need any special tool- just a brush) also put a new fuel filter, every things works fine. Thank you Thank you & Thank you every ones for input.
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