Audi A5 B9 2.0 TDI

The DPF requires regular passive regeneration during sustained driving at higher RPMs. Cars used primarily for trips under 15 km often fail to complete regeneration cycles, as exhaust temperatures need to reach 350-600 degrees Celsius. Soot builds up progressively, triggering a DPF warning light and power reduction. Forced regeneration at a workshop costs around €150-400. Professional chemical cleaning runs €400-800. If the DPF is beyond cleaning, replacement costs €1,500-2,500 depending on parts choice. The B9 generation monitors soot loading precisely via the MMI; ask to see the DPF soot level reading via VCDS or OBDeleven before purchase. Prevention is straightforward: regular motorway runs of 30+ minutes at 2,500+ RPM.

Early B9 diesels (2016-2018) frequently experience AdBlue-related faults, typically between 30,000-80,000 km. The most common component to fail is the NOx sensor (€350-700 to replace), followed by the AdBlue dosing module and heater unit. Symptoms include a threatening 'No restart in X km' countdown warning on the dashboard. In cold climates, the AdBlue heater is particularly prone to failure as the fluid crystallises and blocks the injector. The complete AdBlue tank and pump assembly replacement costs €1,200-2,000 at a dealer. Post-2019 facelift models (B9.5) have significantly improved hardware with updated NOx sensors and more reliable heater elements. When buying, check for any stored AdBlue-related fault codes and verify the system is functioning correctly.

The B9 platform uses a plastic thermostat housing integrated with the water pump assembly that is prone to cracking and leaking coolant. This affects both TDI and TFSI engines. Symptoms include low coolant warnings, visible coolant puddles under the car, and erratic temperature gauge readings. The thermostat housing and water pump are two halves of the same assembly; when one fails, many specialists recommend replacing both simultaneously. Independent shop repair costs €500-800; Audi dealer quotes typically run €1,000-1,400. Audi issued an extended warranty covering this component for 8 years from original in-service date on some models. Check whether your specific VIN is covered before paying out of pocket.

The EGR valve accumulates carbon deposits over time, particularly on engines driven gently at low RPMs or used for short trips. Symptoms include rough idle, hesitation during acceleration, increased fuel consumption, and the engine management light. Professional cleaning of the EGR valve costs €200-400 and can restore normal function. If the valve or its integrated cooler needs full replacement, costs run €600-1,200 depending on whether you use an independent specialist or Audi dealer. The EGR cooler can also develop internal leaks that allow coolant into the exhaust. Regular motorway driving and periodic high-RPM use helps prevent carbon buildup. EGR issues often appear alongside DPF problems, as both are worsened by the same driving patterns.

The DL501 (0B5) 7-speed S-tronic is the standard automatic for quattro-equipped A5 models. The mechatronic unit is the most common failure point, with internal printed circuit boards and sensors degrading from constant exposure to hot transmission oil. Symptoms include harsh downshifts, a jerky lunge when coming to a stop (shifting from 2nd to 1st), loss of reverse, and gearbox malfunction warnings. The G676 driver position sensor is a documented weak point. Mechatronic repair at a specialist costs €1,500-2,500; complete unit replacement at Audi runs €2,500-3,500. Regular S-tronic oil changes every 60,000 km are essential prevention and should not be extended beyond this interval despite some advice suggesting it is a lifetime fill. Manual gearbox cars are not affected.

The turbo actuator can stick due to carbon buildup, particularly on cars driven gently at low RPMs. Symptoms include the EPC warning light, limp mode, and loss of power. The actuator alone can be repaired or replaced at a specialist for €500-900. However, if turbo internals are damaged (worn bearings, shaft play, or oil contamination), a complete turbo replacement costs €1,500-2,500 including labour. Full turbo failure is uncommon before 120,000 km on well-maintained engines. Regular spirited driving and occasional higher-RPM use help prevent actuator sticking.

LED headlights frequently develop condensation on the inside of the lens because LEDs emit far less heat than xenon or halogen bulbs. Audi's own TSB and owner's manual state this is a normal characteristic, as headlights are open ventilation systems. The moisture should clear after driving on a motorway with low beams on. However, when water droplets pool at the bottom of the housing rather than just misting the lens, this indicates faulty seals requiring replacement. Early B9 cars (2016-2017) have a higher incidence due to faulty air vents. Seal and vent repair typically costs €200-400 per headlight; full headlight assembly replacement is €600-800 per side if seals cannot be fixed.

The window regulator uses an internal cable and pulley system that can fray over time. The frayed cable strands jam inside the plastic gear, causing the window to stop moving or move very slowly. This is a documented pattern on B9 Audis, with dealers reporting multiple identical failures. Aftermarket regulators cost around €80-120 for the part; labour runs €100-150. Audi dealer replacement quotes are typically €350-500 per window. The driver's window fails most frequently due to the highest usage.