Audi A4 (B8) 2.0 TDI Fuel Tank Expanding and Refusing Fuel: A 3,000-Mile Chronology

If you own a 2013 Audi A4 (B8) 2.0 TDI and have just stood at a petrol station watching the pump nozzle click off repeatedly while your tank is still half empty, do not ignore it. Before you assume it is just a sensitive forecourt pump, walk around to the back doors, open them up, and check your rear seat bench.

If the rear seat cushion looks slightly raised, feels tight, or the metal floor pan underneath has bowed upwards, your plastic fuel tank is physically inflating under pressure.

Over the course of nine months and just 3,013 miles in my 2013 Audi A4 2.0 TDI (engine code CGLC), I went through three separate fuel tanks and over £5,280 in garage bills before finally writing the car off for £320. Because this fault rarely triggers a dashboard warning light, it completely baffles mechanics who rely solely on diagnostic laptops.

If you are facing these symptoms, here is what to look out for, the exact chronology of what we replaced, and why partial fixes on this fuel system rarely work.

The Early Symptoms to Spot

• Pump Kick-Back at the Filler Neck: The diesel pump clicks off immediately when you try to fill the car, or fuel backs up into the neck as if the tank is already full. Air and vapour inside the tank cannot escape fast enough to let liquid diesel in.

• A Raised Rear Seat Base: As the high-density polyethylene tank balloons underneath the car, it runs out of room downwards and pushes straight up into the thin metal floor pan beneath the rear passenger seats, causing excessive structural damage to the floor.

• Power Loss and Hesitation: The engine feels starved of fuel under load or struggles to run smoothly.

• No Engine Management Light: Crucially, your dashboard can remain completely clear of engine fault codes even while the tank is physically deforming under the car.

• Late-Stage Secondary Symptoms: As the wider fuel system degrades, you may see intermittent oil pressure warnings on the dash, rough starting, and thick white smoke smelling of raw diesel on cold starts.

The Chronology: 3,013 Miles and Three Fuel Tanks

Stage 1: Fuel Contamination and Tank Number One (205,198 Miles, January 2026)

The saga began at 205,198 miles where the original fuel tank expanded and refused to take fuel. A local garage sourced a replacement second-hand tank shell, swapped the original in-tank low-pressure fuel pump and sender unit over into the replacement tank, and put the car back on the road.

Stage 2: The Second Tank Balloons and a £3,111 Rebuild (205,673 to 205,679 Miles, March to May 2026)

Less than 500 miles later, the second tank expanded in the exact same way. When the car was plugged into VCDS on 11 March 2026 at 205,673 miles (331,000 km), the Engine Control Module (Address 01) reported "No fault code found". Because the fuel tank breather pipes and mechanical venting valves have no electronic sensors, the computer thought the fuel system was healthy.

By May 2026, at 205,679 miles, the car had to be transported on a flatbed recovery truck to an independent VAG specialist. After four hours of initial diagnostic checks, they drained and removed the bloated tank. Inside, they found heavy debris, including leaves and general dirt left behind from the previous fitting. They also noted excessive damage to the rear floor under the back seat where the expanding tank had forced the metal upwards.

At this point, we hit the major catch with modern common-rail diesels. Official Audi repair guidelines state that whenever fuel contamination is found, the entire fuel system must be replaced: the tank, low-pressure pump, fuel filter, high-pressure fuel pump (HPFP), fuel injectors, leak-off return pipe, fuel rail, and sensors.

Because a complete genuine system replacement would have easily exceeded the value of a 205,000-mile car, we attempted a targeted mechanical overhaul (totalling £3,111.38 including VAT), we replaced the following components:

• Tank and Lift Pump: A complete second-hand fuel tank and matching in-tank low-pressure pump supplied from a breaker.

• High-Pressure Fuel Pump (HPFP): A brand-new Bosch high-pressure pump (£767.40 plus VAT for the part) along with a seized high-pressure fuel pipe.

• Return and Filtering Circuit: A new fuel leak-off return pipe (£126.00 plus VAT), a new high-pressure sensor (£78.90 plus VAT), a new fuel filter, and a missing blanking plug.

• Timing Belt: A genuine cambelt kit complete with water pump and coolant (£630.00 plus VAT).

To keep costs remotely sensible, the original fuel rail and the old fuel injectors were left in the vehicle. Following an extended road test, the garage reported no active faults.

Stage 3: Oil Pressure Warnings and Timing Codes (206,533 to 207,190 Miles, July to August 2026)

For around 1,000 miles, the car seemed usable. However, trouble was brewing in the engine bay. According to the VCDS freeze-frame data pulled during the next visit, two vital engine fault codes were logged in early July 2026:

• Fault Code P0016 (Camshaft Position Sensor G40 / Engine Speed Sensor G28 Incorrect Correlation): Logged on 1 July 2026 at 332,382 km (approx. 206,533 miles), just 854 miles after the cambelt replacement.

• Fault Code P164D (Oil Pressure Switch for Reduced Oil Pressure Malfunction): Logged on 3 July 2026 at 332,557 km with an engine oil temperature of 86.2°C and fuel temperature of 41.0°C.

On 11 August 2026, at 207,190 miles, the car went back in for its overdue 20,000-mile service, a new oil pressure switch, an exchange air conditioning compressor, a front outer CV boot kit, and a rear parking sensor, costing a further £2,170.34.

On that August invoice, the technician left a telling warning regarding the oil light: while the oil pressure switch was replaced, they were "unable to rule out internal issue due to diluted oil or blocked oil pump strainer" following the previous multiple fuel pressure issues.

Stage 4: Tank Number Three Expands and Cold-Start White Smoke (208,211 Miles, October 2026)

At 208,211 miles, just 1,021 miles after the August service and 2,532 miles after the May fuel system rebuild, the fault returned in full force:

1. The fuel filler neck refused to take diesel again.

2. The back seat pushed upwards as the third fuel tank ballooned underneath the floor.

3. On cold starts, the exhaust began billowing white smoke accompanied by the smell of unburnt diesel.

What Was Actually Happening Under the Bonnet (and Floor)

Looking at the complete picture across all 3,000 miles, two separate chains of failure were happening simultaneously.

1. Why Three Tanks Ballooned Replacing the high-pressure Bosch pump, the fuel filter, and the engine-bay leak-off pipe did not stop the tank from inflating. A plastic tank only expands like a balloon when positive pressure cannot escape, either because return fuel is overheating or because the mechanical breather system is blocked. On the B8 A4, if the rollover gravity valve, the filler neck breather pipe, or the vent canister behind the wheel arch is blocked (or if a second-hand tank comes from a breaker with a seized vent valve), air cannot displace when filling and hot vapour cannot escape when driving. Because there is no pressure sensor in the diesel breather line, a diagnostic scan will never spot it. The only way to prove it before fitting another tank is a physical smoke and pressure flow test through the vent lines.

2. Why the Oil Diluted and White Smoke Appeared Leaving the original 205,000-mile fuel injectors in the engine after a fuel contamination incident proved fatal. Once injectors suffer internal wear or contamination from petrol and debris, they no longer atomise fuel cleanly and begin leaking or over-fuelling into the bores. On a cold start, that unburnt raw diesel passes straight into the exhaust as white smoke. Worse still, excess diesel washes past the piston rings into the sump, thinning out the engine oil, causing oil dilution, and triggering the P164D oil pressure switch fault. Combine that with internal wear triggering the P0016 timing correlation fault, and the engine itself becomes economically unviable to save.

Advice for Other Audi B8 Owners

If your Audi A4 2.0 TDI refuses fuel at the pump and your back seat rises, learn from my £5,281.72 mistake:

• Do not just swap the fuel tank: Never fit a bare tank and transfer your old pump and breather valves over without testing them off the car. You will simply transfer the fault to the new tank.

• Demand a physical breather test: Insist that your garage performs a manual smoke and air-flow test on the filler neck, rollover valve, and breather circuit down to the wheel arch vent before spending a penny on parts.

• Respect the contamination rule: If your car has suffered fuel contamination or metal swarf in the tank, replacing the HPFP and tank while leaving the old injectors and rail in place is a massive gamble. If your car has high mileage, weigh up the total cost of injectors, pumps, and breather gear right at the start, before you end up £5,000 deep into a car worth £320 in salvage.

British Airways 747 London to Phoenix First Class Experience

Entering First Class Galeries Lounge in Terminal 3 at Heathrow is suitably classy and impressive leading straight into the Champagne Bar

A coffee station area gives the range of hot drinks one would expect 

Lounge areas offer a variety of seating options for individuals or small groups with easy or more upright seating

Refreshments available with a range of beers, wines and spirits 

Buffet of food available to match the time of day with a range of cold and hot options

Dining space is available with further menu of items available to request for table service or in the lounge areas.

A number of magazines and newspapers available for reading 

As well as a work zone of computers and multi-function printer

Then first to board, the cabin is literally at the very front of the plane as the pilots are on the level above and further back so First Class passengers indeed arrive at the deistination first 

to the seat...

Even a cupboard for one's coat!

Pyjamas were offered in medium or large with a toiletry bag which seemed well provisioned.

Naturally champagne was offered prior to departure and for a cabin of just of 14 it is good to see 2 or 3 members of staff offering of course the staff attention ratio to be expected in this premium cabin.

Aperitif with roasted nuts (not packet stuff at the front so lovely and warm) are served as lunch orders from a selection of 4/5 choices for starters and main are taken with wine suggestions...

As avid consumer of tech the 20-year old technology apparent in the screen has to be the most obvious flaw. I assume the core technology feeds the whole plane or else why wouldn't at least the top cabin have a quality screen; however, the slightly larger screen especially when further away from the seat is appreciated as is a USB socket for charging (power socket also available by foot stool). Without wanting to labour the point when at home one can enjoy voice activation, streaming of any content this felt a very old school way of controlling the entertainment and took away from a key part of a top of the range cabin experience for the trip.

Moving on from the unintentional irony of my photo being from a sci-fi film, it is a film that would be best appreciated on a decent screen rather than something that feels decades old. The headphones provided give good audio and noise-cancelling so as in previous Business (Club) class no need to break out one's own. 

Now to lunch, with attendant pulling out the tray and cloths very nice start...

Starter as equisite of course, in this case seared tiger prawns and scallop with umami crumble, Marie Rose sauce, avocado purée and cucumber salad...

Mains equally showed a freshly served look for a seated fillet of Aberdeen Angus beef with pearl barley arancini, cauliflower purée, root vegetables and Madeira jus...

Followed by desert and cheese options, coffees and chocolate.

When it comes time to relax (I paused the entertainment for the meal only for it to seal it's fate as sub-standard by failing to keep my place), as one would expect one is in control of the seating with a luxurious twist dial 

The foot stool is comfortable and can then become a lie flat bed or seat for a meeting, presumably for an underling!

Even the toilet has a window (with blind)! 

Other than that the addition of facecloths as an alternative to paper towels was a nice touch.

A light bite meal followed in the last hour or so before landing, started with a salad...

Followed by braised Moroccan-style lamb slider with tomato relish, baba ghanoush and slaw salad.

Then followed be fruit and coffees or teas.

Is first class worth it? The very fact you have to ask then maybe not! Like so many things in this world, the only reason to maybe do it is because you can.