EXPERT IN AUTO PARTS
5 December 2025 (updated) Table of Contents
The AdBlue system in the Audi A4 B9 frequently malfunctions, particularly in the 2.0 TDI 150 PS and 2.0 TDI 190 PS diesel engines, which manifests itself in various error messages in the instrument cluster. The symptoms range from "Check AdBlue system" to drastic warnings about engine start blocks after a certain number of kilometres. These common faults typically occur between 30,000 and 80,000 kilometres and can be caused by both clogged AdBlue lines and defective NOx sensors. The tank cap of the AdBlue tank can also leak, leading to crystallisation and other problems. The reliability of the entire exhaust gas aftertreatment system is significantly impaired as a result and the vehicle will no longer start if the warnings are ignored.
Regular maintenance is essential for the proper functioning of the exhaust aftertreatment system. The sensitive Audi A4 B9 AdBlue components require special attention during maintenance, especially the regular inspection of the lines and sensors every 15,000 kilometres. Using high quality AdBlue and avoiding contamination can prevent many of these problems and significantly extend the life of the system.
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OPEL GM Engine oil
5W-30, 5l, Synthetic Oil
Article number: 19 42 003
£38.99
£7.80
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 3 397 016 507
£8.99price incl. 20% VAT, excl. delivery costs
VAG Engine oil
5W-40, 5l
Article number: GS55502M4
£48.49
£9.70
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: GS60577M2
£14.99
£14.99
for 1 litre
price incl. 20% VAT, excl. delivery costs
SKF Bellow Set, drive shaft
146 mm, Wheel Side, Front Axle, with clamps
Article number: VKJP 01001
£14.49£28.98 / Price per 2 items
price incl. 20% VAT, excl. delivery costs
The S-Tronic dual-clutch transmission of the Audi A4 B9 develops characteristic weaknesses that manifest themselves in jerky gear changes, delayed gear changes and unusual noises. These faults occur particularly frequently between 60,000 and 100,000 kilometres and initially manifest themselves as slight jerking when starting off or changing gear. The automatic transmission no longer shifts smoothly and shows symptoms such as clutch grinding or complete failure of individual gears. The breakdowns can have both mechanical and electronic causes, with the mechatronic unit being particularly susceptible to defects. In the case of advanced problems, the transmission no longer functions properly and can lead to costly repairs that often require the replacement of the entire clutch unit.
An expert inspection is required to recognise early signs of transmission problems. The precise Audi A4 B9 S-Tronic transmission parts require regular oil changes every 60,000 kilometres and careful monitoring of the operating temperature. A professional diagnosis with special Audi software can reveal hidden fault codes and enable preventive measures to be taken before major damage occurs.
The diesel particulate filter (DPF) of the Audi A4 B9 is prone to clogging, especially on frequent short journeys and at low operating temperatures. These complaints are manifested by reduced engine performance, increased fuel consumption and characteristic warning messages in the instrument cluster. The particulate filter typically becomes clogged between 40,000 and 70,000 kilometres, although vehicles with predominantly urban operation are affected earlier. The symptoms often begin with occasional regeneration cycles, which are noticeable through increased engine speed and temperature. If the filter is too dirty, automatic regeneration no longer works and error messages appear. In advanced cases, the vehicle will no longer start properly or will exhibit significantly reduced performance, which considerably impairs the reliability of the engine.
A systematic check is necessary to assess the condition of the particulate filter. The Audi A4 B9 particulate filter systems require regular motorway journeys of at least 20 minutes every 500 kilometres to ensure complete regeneration. Preventive maintenance with special cleaning additives and regular long-distance driving can extend the service life of the filter to over 150,000 kilometres.
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-13%
Article number: 15F7E5
compared to
RRP
£50.65
£43.99
£11.00
for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 0 986 479 E49
£71.99
Price per item
£143.98 / Price per 2 items
price incl. 20% VAT, free delivery
BOSCH Glow plug
4,4V M 10 x 1, Rod Glow Plug, Length: 130 mm, 10 Nm, 63, Duraterm
Article number: 0 250 403 009
£12.49
Price per item
£49.96 / Price per 4 items
price incl. 20% VAT, excl. delivery costs
Valvoline Engine oil
5W-30, 4l
Article number: 872378
£40.49
£10.12
for 1 litre
price incl. 20% VAT, excl. delivery costs
-24%
LIQUI MOLY Engine oil
5W-30, 5l, Synthetic Oil
Article number: 3756
compared to
RRP
£73.77
£55.99
£11.20
for 1 litre
price incl. 20% VAT, excl. delivery costs
The air conditioning system of the Audi A4 B9 shows various weak points, which can manifest themselves in insufficient cooling capacity, unusual noises and complete failure. These common faults occur between 20,000 and 60,000 kilometres and affect both the compressor and the refrigerant lines. The symptoms often start with reduced cooling capacity and can develop into complete cooling failure. Leaking condensers and defective expansion valves lead to refrigerant loss, while clogged cabin filters impair air circulation. In severe cases, the air conditioning system stops working and requires costly repairs. Frequent use and extreme temperatures put additional strain on the reliability of the system, leading to premature component wear.
Professional maintenance is crucial for the longevity of the air conditioning system. The complex Audi A4 B9 air conditioning components require annual checks of the refrigerant level and regular replacement of the cabin filters every 15,000 kilometres. Preventive disinfection of the evaporator and checking all seals can prevent many problems and ensure that the system functions optimally.
The drive shaft of the Audi A4 B9 develops characteristic noises and vibrations that occur particularly when cornering and accelerating. These breakdowns typically manifest themselves between 80,000 and 120,000 kilometres through clicking or cracking noises from the front wheels. The symptoms are caused by worn joints or damaged boots, which lead to lubrication problems. At the same time, the Bluetooth system shows frequent disconnections and compatibility problems with modern smartphones. These faults manifest themselves in interrupted phone calls, music streaming problems and difficulties with device pairing. The complaints affect both the hardware and the software components of the infotainment system and can significantly impair the user experience.
Regular maintenance is essential for the proper functioning of both systems. The Audi A4 B9 drive shaft joints require regular checks of the boots and timely replacement at the first sign of damage every 60,000 kilometres. The Bluetooth system requires regular software updates and occasional resets of the connection settings to ensure optimum compatibility and reliability.
Based on the experience of Audi A4 B9 drivers, the following additional problems occur:
| Strengths | Weak points |
|---|---|
| High-quality workmanship | AdBlue system problems |
| Modern assistance systems | S-Tronic transmission susceptibility |
| Comfortable ride quality | Particle filter blockage |
| Good engine range | Air conditioning defects |
| Elegant design | Electronic faults |
| Solid road holding | High repair costs |
| Good resale value | Bluetooth connectivity issues |
The Audi A4 B9 proves to be a technically sophisticated vehicle with modern systems which, however, require regular maintenance and expert care. Most problems can be avoided through preventive measures and timely intervention. The exhaust aftertreatment systems and electronic components in particular require attentive care in order to guarantee the characteristic Audi quality and longevity.
GATES Water pump and timing belt kit
with water pump
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BOSCH Tyre pressure sensor (TPMS)
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FEBI BILSTEIN Crankshaft seal
with flange, frontal sided, PTFE (polytetrafluoroethylene)
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INA Water pump
with belt pulley, with gasket/seal, with thermal management module, with housing, for timing belt drive
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YUASA Battery
12V 80Ah 800A AGM Battery
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GATES Water pump and timing belt kit
with water pump, with integrated disabling contact, switchable water pump
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MOTUL Engine oil
5W-30, 5l
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NRF EGR Module
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ELRING Clamp, exhaust system
Ø: 75mm
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NGK Spark plug
M14 x 1,25, Spanner Size: 16 mm
Sold by AUTODOC