Used Audi A8 (D4) review

Exterior:

• Water Leakage:
  • Common issue with water leaking into the cabin from around the sunroof area.
  • Often due to blocked sunroof drainage holes or a small gap between the top of the windscreen and the car body.
  • Proper fix involves fitting a new windscreen, which should be genuine Audi glass to avoid issues with sensors and cameras.
  • Sensors and cameras need recalibration after windscreen replacement, adding to the cost.
• Sunroof Drainage:
  • Essential to keep sunroof drainage holes clear to prevent water from entering the interior.
  • Water buildup can cause significant damage to the electronics behind the dash and interior trim.
• Electronic Issues:
  • Common failures include motors for the powered boot, adaptive headlights, powered mirrors, and windows.
  • Condensation inside the tail lights is frequently reported.
  • Foot-detecting boot opening technology can fail sporadically.

Interior:

• MMI Screen Issues:
  • Problems with the MMI screen rising from the dash; sometimes it struggles or fails to rise.
• Rearview Mirror Camera:
  • Camera behind the rearview mirror can fail due to solder joints separating from temperature changes.
  • Replacement parts are often unavailable from Audi, requiring used parts to be coded and calibrated.
• Electronic Handbrake:
  • Issues with the electronic handbrake getting stuck, often due to wiring problems, sometimes necessitating towing.
• General Electronic Failures:
  • Numerous reports of powered seat adjusters, infotainment glitches, slow tech responses, non-functional buttons, and sunroof failures.
  • Important to test every function and button when buying to ensure all features work properly.
  • Infotainment system issues might be resolved with a software update.
• Non-Electronic Issues:
  • Interior piano black plastic trim is prone to scratching.

Mechanically:

3.0L Diesel DOHC 24v Turbo Direct Injection V6 (CDTC, CDTA, CMHA)

• General Reliability: This engine is known for its robustness and is not typically prone to catastrophic failures. However, it is not without its problems.
• Coolant and Oil Leaks: Leaks are common from components located in the engine valley, including the oil filter housing, EGR cooler, and oil cooler. These issues are labor-intensive and costly to repair.
• Heat Damage: Over time, the heat from the turbos can cause the surrounding plastics and components to fail, leading to further issues.
• EGR Cooler Leaks: Internal leaks in the EGR cooler can lead to misdiagnoses as head gasket issues because the leaks can seep into the exhaust system.
• EGR Valve and Inlet Clogging: The EGR valve is prone to clogging, and the entire inlet system can become choked with buildup, which can cause the variable intake manifold actuator to fail.
• Fuel System Issues: The high-pressure fuel pump can occasionally have issues, and injector seal leaks are becoming more common, leading to reduced engine performance and reliability.

4.2L Diesel DOHC 32v Turbo Diesel Direct Injection V8 (CDSB Euro 5)

• Design Complexity: This engine is essentially two 2.0L engines side-by-side, making it complex with two of each component (ECU, MAF & MAP sensors, crank sensors), complicating fault diagnosis.
• Harmonic Balancer Issues: The engine can suffer from harmonic balancer problems, which can cause vibrations and additional wear.
• EGR Problems: EGR issues are frequent, contributing to engine performance problems and increased emissions.
• Thermostat and Water Pump Failures: Premature failures of these components are typical for Volkswagen Group vehicles, leading to overheating and potential engine damage.
• Oil Leaks and Consumption: Regularly reported oil leaks and excessive oil consumption can lead to frequent top-ups and potential engine damage if not managed.
• Engine Mount Wear: The engine mounts, designed to absorb vibrations, are very soft and thus wear out prematurely, necessitating expensive replacements.

4.0L Petrol Twin Turbo DOHC 32v Intercooled Direct Injection V8 (CGTA, CTFA)

• PCV and Oil Separator Issues: Problems with the PCV or oil separator can cause vacuum leaks, leading to lean air-fuel ratio faults and impacting engine performance.
• Coil Issues: Coil failures are a common issue, leading to misfires and reduced engine efficiency.
• Thermostat and Coolant Leaks: Like other engines in the lineup, thermostat and coolant leaks are prevalent, leading to overheating risks.
• Turbo Failures: Turbo failure is a significant issue, often due to clogged oil supply lines and filter screens, which result in oil starvation. This is exacerbated by long or missed service intervals. Preventative maintenance, including changing oil line screens, is essential to avoid costly turbo replacements.
• Engine Mount Failures: Similar to the 4.2L Diesel, the soft engine mounts often fail and are expensive to replace, impacting the overall smoothness of the ride.

4.2L Petrol DOHC 32v Direct Injection V8 (CDRA Euro 5)

• Oil Leaks: Common oil leaks originate from the timing cover, oil filter housing, and valley cover, necessitating regular checks and maintenance.
• Timing Chain Complexity: The timing chains are located at the rear of the engine, making access extremely complex. While not overly common, timing chain guide failures can lead to catastrophic engine failure, requiring engine removal for repairs.

General Engine Notes:

• Timing Chains: All these engines feature rear timing chains, a common design among European manufacturers. While not a frequent issue in well-maintained, low-mileage cars, neglected and high-mileage vehicles can suffer from timing chain failures. Maintenance or repairs involving timing chains are extremely costly due to the necessity of removing the engine and transmission.
• Complexity of V8 Engines: The V8 engines in these models are among the most complex, designed to maximize space efficiency but making them difficult and expensive to work on. Modified S8 models can produce high horsepower but often at the expense of reliability and longevity; it is advisable to avoid modified versions to ensure long-term durability.

Transmission:

• ZF 8HP Transmission: The D4 A8 and S8 models are equipped with the ZF 8HP transmission, a highly reliable unit found in many vehicles across different manufacturers. It is praised for its smooth shifting and durability, contributing to the overall reliability of these models.

Suspension:

• Air Suspension: The air suspension system, while generally reliable, can suffer from several issues, including leaking airbags, hardware and sensor problems, and electronic complications. Regular maintenance can help mitigate these issues, but repairs can be costly.
• Control Arm Bushes: The lower control arm bushes are a known weak point, often requiring replacement to maintain proper suspension performance and ride quality.

Electronics:

• Complex Systems: The A8 and S8 are equipped with a multitude of systems, sensors, and ECUs that control virtually every aspect of the vehicle. This complexity can lead to reliability concerns, with electronic issues often being difficult and expensive to diagnose and repair. Electronic gremlins are a common cause of significant repair costs, sometimes making it financially unviable to keep the vehicle.

Additional Considerations

• Overall Reliability:
  • The D4 A8 and S8 are loaded with advanced electronics and luxury features, but they are known for questionable reliability.
  • High depreciation rates make these vehicles more affordable on the second-hand market, but potential buyers should be prepared for high repair and maintenance costs.
• Maintenance:
  • Regular maintenance of drainage systems and electronic components is crucial to avoid costly repairs.
  • Genuine parts and proper recalibration of sensors are essential to maintain functionality.

By being aware of these common issues and conducting thorough inspections, potential buyers can make informed decisions about purchasing a used Audi D4 A8 or S8. Despite their luxurious appeal, these vehicles require diligent upkeep to ensure they remain reliable and enjoyable to drive.