The Mercedes-Benz S-Class W222 S 400 is a pinnacle of luxury, engineering, and advanced technology. It represents the ultimate blend of sophistication and performance, offering unparalleled comfort and state-of-the-art features. However, like any high-end vehicle, the W222 S 400 is not immune to mechanical and electrical issues. Despite its solid build quality, long-term owners have reported recurring problems that affect reliability, performance, and maintenance costs.
This in-depth guide explores the most common problems associated with the Mercedes-Benz S 400 W222, their causes, symptoms, and possible solutions. Whether you are an existing owner or considering purchasing a used S 400, understanding these potential issues will help you make an informed decision and maintain the car properly.
Mercedes S-Class W222 S 400 Engine and Performance Issues
The Mercedes-Benz S 400 features a 3.0L twin-turbocharged V6 engine, known for its smooth power delivery and refined performance. However, certain mechanical issues can arise over time, potentially leading to costly repairs if not addressed promptly.
Turbocharger Failure
One of the most significant concerns with the W222 S 400 is turbocharger failure. Turbochargers enhance engine efficiency by forcing more air into the combustion chamber, but they are prone to failure due to carbon buildup, oil contamination, or actuator malfunctions. A failing turbocharger can lead to a noticeable loss of power, excessive smoke from the exhaust, and a whining noise from the engine bay. In severe cases, the turbo may completely seize, leading to costly repairs.
Regular oil changes using high-quality synthetic oil help prevent carbon buildup inside the turbocharger. If you experience performance issues, it's crucial to have the turbo system inspected by a professional. Early detection can prevent further damage to the engine and reduce repair costs.
Engine Misfires and Rough Idling
Another common problem in the S 400 is engine misfires and rough idling. These symptoms are typically caused by failing ignition coils, worn-out spark plugs, or excessive carbon deposits on the intake valves due to direct injection. Misfires not only lead to jerky acceleration but also result in decreased fuel efficiency and increased emissions. If left unchecked, unburnt fuel can damage the catalytic converter, leading to even more expensive repairs.
To prevent misfires, regular maintenance such as spark plug replacement and intake valve cleaning is essential. Using high-quality fuel with proper detergents can also reduce carbon buildup inside the engine.
Excessive Oil Consumption and Leaks
Some S 400 owners have reported unusually high oil consumption between service intervals. This issue is often linked to worn valve cover gaskets, oil cooler seal leaks, or degraded piston rings. Over time, these components wear out, causing oil to escape and forcing owners to top up their oil frequently. If ignored, oil leaks can lead to reduced engine lubrication, increased wear, and potential engine failure.
To address this issue, it's important to check oil levels regularly and inspect for leaks. Replacing defective gaskets and seals can help maintain optimal oil levels and prevent excessive oil consumption.
Mercedes S-Class W222 S 400 Transmission Problems
The W222 S 400 is equipped with either a 7-speed (7G-Tronic) or a 9-speed (9G-Tronic) automatic transmission, designed for smooth and seamless shifts. Despite their advanced engineering, these transmissions have been known to develop various issues over time.
Hard Shifting and Transmission Hesitation
One of the most frequently reported transmission issues is rough shifting or delayed gear engagement. Owners have experienced instances where the transmission hesitates before shifting, engages gears too aggressively, or slips under acceleration. These problems are often caused by degraded transmission fluid, software issues within the transmission control unit (TCU), or mechanical wear in the gearbox components.
Regular transmission fluid and filter changes can prevent many of these problems. Mercedes recommends changing the transmission fluid every 60,000 km to ensure smooth operation. If shifting problems persist, a transmission adaptation reset or software update may be necessary.
Torque Converter Issues
Another issue that affects the transmission is torque converter shudder, which causes a noticeable vibration when accelerating at low speeds. This is typically caused by deteriorated transmission fluid that no longer provides proper lubrication. If left untreated, it can lead to increased wear and possible transmission failure.
A full transmission fluid flush using the manufacturer-recommended fluid often resolves the issue. If the shuddering continues, a torque converter replacement may be required.
Mercedes S-Class W222 S 400 Suspension and Ride Comfort Issues
The Mercedes S-Class is renowned for its exceptional ride quality, largely due to its advanced suspension system. However, certain suspension-related problems can develop over time, affecting both ride comfort and handling.
AIRMATIC Suspension Failures
The AIRMATIC air suspension system in the W222 S 400 allows for adjustable ride height and adaptive damping. While it provides a smooth and comfortable ride, it is prone to failure, leading to uneven ride height, excessive bouncing, and a harsh driving experience. Owners have reported instances where the car sags to one side, takes longer to raise, or sits lower after being parked overnight.
Common causes of AIRMATIC suspension failure include leaking air struts, a malfunctioning air compressor, or faulty ride height sensors. If left unaddressed, a failing air strut can put excessive strain on the compressor, leading to its premature failure. Replacing worn-out air struts early can prevent more costly repairs in the future.
Control Arm and Bushing Wear
Another suspension-related problem is premature control arm and bushing wear. The suspension control arms are crucial for maintaining stability and absorbing road imperfections. Over time, the rubber bushings in these components degrade, leading to clunking noises, poor handling, and increased road vibrations.
Replacing worn-out bushings and control arms restores ride quality and improves steering responsiveness. Regular suspension inspections can help identify potential issues before they lead to costly repairs.
Mercedes S-Class W222 S 400 Electrical and Technology Problems
The Mercedes S 400 is equipped with an array of high-tech features and electronic systems, but these can also be sources of frustration for owners. Electrical issues can be particularly troublesome due to their complexity and the difficulty in diagnosing the root cause.
COMAND System Malfunctions
The COMAND infotainment system serves as the central hub for navigation, entertainment, and vehicle settings. However, many owners have reported issues such as system freezes, unresponsive controls, and random restarts. These problems are often caused by software glitches, failing control modules, or connectivity issues.
Performing a system reset or updating the COMAND software usually resolves minor glitches. However, if the system continues to malfunction, replacing the main control module may be necessary.
Keyless-Go and Start/Stop System Failures
The Keyless-Go system in the S 400 allows for keyless entry and push-button start functionality. Some owners have reported instances where the key fob fails to communicate with the vehicle, preventing it from starting. This problem can be caused by a weak key fob battery, signal interference, or a faulty keyless entry module.
In many cases, simply replacing the key fob battery resolves the issue. If the problem persists, reprogramming the key or diagnosing the keyless entry module may be required.
Battery Drain and Charging Issues
Battery drain is another common electrical problem in the S 400, especially in models equipped with numerous electronic features. A weak battery can lead to issues such as dim dashboard lights, difficulty starting the vehicle, or warning messages related to battery voltage.
Common causes of battery drain include faulty alternators, parasitic draws from malfunctioning electronic components, or excessive use of power-consuming features such as heated seats and infotainment displays. Performing a battery test and checking the alternator output can help identify the source of the problem.
Mercedes S-Class W222 S 400 Cooling System and Overheating Issues
A well-functioning cooling system is essential to keep the Mercedes S 400’s engine operating at the optimal temperature. However, certain weaknesses in the cooling system design can lead to overheating, coolant leaks, and potential engine damage.
Radiator and Coolant Hose Leaks
One of the most common cooling system failures in the W222 S 400 is radiator and coolant hose leaks. Over time, the plastic and rubber components in the cooling system degrade due to exposure to high temperatures and pressure. This can result in coolant leaks, which reduce cooling efficiency and increase the risk of overheating.
Typical symptoms include low coolant levels, visible coolant puddles under the car, and rising engine temperatures. It’s important to inspect coolant hoses and the radiator regularly for signs of cracks, leaks, or wear. If a leak is detected, replacing the affected component promptly can prevent engine overheating and further damage.
Water Pump and Thermostat Failures
The water pump and thermostat regulate coolant circulation and engine temperature. A failing water pump may cause coolant flow to be insufficient, leading to overheating. Meanwhile, a faulty thermostat can become stuck, either restricting coolant flow or allowing excessive circulation, both of which can cause temperature fluctuations.
Common symptoms of these failures include inconsistent engine temperature readings, overheating warnings, and reduced heater performance. Replacing a faulty water pump or thermostat at the first sign of trouble can prevent more severe engine damage.
Mercedes S-Class W222 S 400 Braking System Issues
The braking system in the Mercedes S 400 is engineered for both performance and safety, but like any high-performance vehicle, it is not immune to wear and potential malfunctions.
Premature Brake Wear
Many owners have reported that the brake pads and rotors on the W222 S 400 wear out faster than expected, requiring frequent replacements. This is partly due to the vehicle’s weight and the performance-oriented braking system, which generates significant heat during operation.
Signs of excessive brake wear include squealing or grinding noises, longer braking distances, and pulsation in the brake pedal. Regular inspection of brake components and timely replacement of pads and rotors can ensure consistent braking performance. Opting for high-quality aftermarket brake components can sometimes provide better longevity than OEM parts.
Brake System Warning Messages
Some S 400 models experience random brake system warning messages on the dashboard, often due to faulty brake sensors or electronic stability control (ESC) module issues. If the brake system warning light appears, it’s crucial to have the system scanned for error codes to determine the underlying cause. In many cases, a software update or sensor replacement resolves the issue.
Mercedes S-Class W222 S 400 Interior Wear and Comfort Issues
The W222 S-Class is known for its luxurious interior, featuring premium materials, advanced climate control, and state-of-the-art seating options. However, certain wear-and-tear issues can develop over time, particularly in high-mileage models.
Seat Bolster and Leather Wear
One common complaint is the premature wear of seat bolsters, particularly on the driver’s side. The constant entry and exit of the vehicle cause stress on the leather, leading to cracks, wrinkles, and fading. Regular conditioning with high-quality leather care products can help preserve the upholstery. In severe cases, reupholstering or using protective seat covers can extend the life of the seats.
Air Conditioning Malfunctions
The climate control system in the S 400 is designed to provide optimal cabin comfort, but some owners have reported issues such as weak airflow, uneven cooling, or AC failure. These problems can stem from clogged cabin air filters, refrigerant leaks, or faulty HVAC control modules. If the AC system is not functioning properly, a full diagnostic check should be performed to identify and repair the issue.
Mercedes S-Class W222 S 400 Fuel System and Injector Problems
The direct fuel injection system in the Mercedes S 400 provides enhanced efficiency and power, but it can develop problems over time, leading to poor performance and increased fuel consumption.
High-Pressure Fuel Pump Failure
The high-pressure fuel pump (HPFP) is responsible for delivering fuel to the engine at the necessary pressure. Over time, the HPFP can wear out, leading to issues such as rough idling, reduced acceleration, and difficulty starting the car. If the HPFP fails, it can cause fuel starvation, potentially damaging the engine.
Replacing the HPFP at the first sign of trouble can prevent further complications. Using high-quality fuel and periodically adding fuel system cleaners can help extend the lifespan of fuel injectors and pumps.
Carbon Buildup in Fuel Injectors
Carbon deposits can accumulate on the fuel injectors over time, causing poor fuel atomization and reduced engine efficiency. Symptoms include hesitation during acceleration, increased fuel consumption, and engine misfires. Professional injector cleaning or replacement is often necessary to restore optimal performance.
Mercedes S-Class W222 S 400 Exhaust System and Emission Issues
The Mercedes S 400 is equipped with an advanced exhaust system designed to meet stringent emission standards. However, components such as the catalytic converter, oxygen sensors, and diesel particulate filter (DPF) (in diesel models) can develop issues over time.
Catalytic Converter Failure
The catalytic converter helps reduce harmful emissions by converting exhaust gases into less harmful substances. However, it can become clogged or damaged due to excessive carbon buildup or engine misfires. A failing catalytic converter can trigger a check engine light, reduce performance, and cause a rotten egg smell from the exhaust.
If a catalytic converter failure is detected, replacing it with an OEM or high-quality aftermarket unit is necessary to maintain emission compliance.
Oxygen Sensor Malfunctions
Faulty oxygen sensors can cause inaccurate fuel-air mixture readings, leading to poor fuel efficiency and increased emissions. If an oxygen sensor issue is detected, replacing it promptly can improve engine performance and reduce fuel consumption.
Mercedes S-Class W222 S 400 Long-Term Maintenance and Ownership Considerations
Owning a luxury vehicle like the Mercedes S 400 requires commitment to regular maintenance and proactive repairs. Many of the common issues discussed in this guide can be prevented or mitigated with proper servicing and timely part replacements.
Regular Servicing is Essential
Routine oil changes, transmission fluid changes, suspension checks, and brake inspections are vital for keeping the S 400 in top condition. Using manufacturer-recommended parts and fluids can prevent premature wear and system failures.
Software Updates and Recalls
Mercedes-Benz frequently releases software updates to fix bugs in the infotainment system, transmission, and electronic control units. Ensuring that your vehicle is updated with the latest software can resolve many minor issues. Additionally, checking for recalls and service bulletins can help identify any factory defects that may require attention.
Conclusion
The Mercedes-Benz S-Class W222 S 400 is a remarkable vehicle, offering a luxurious driving experience and advanced features. However, it is not without its flaws. Common issues such as turbocharger failures, transmission hesitations, AIRMATIC suspension leaks, and electrical system malfunctions can affect reliability if not addressed in time.
To ensure the longevity of your S 400, proactive maintenance and timely repairs are essential. By staying informed about potential problems and taking preventative measures, owners can enjoy a trouble-free experience with this exceptional luxury sedan.
For professional Mercedes-Benz servicing and repairs, visit European Auto Pro 253 Goodwood Road, Kings Park, 5034 South Australia. Our expert technicians specialize in diagnosing and resolving issues specific to the S 400, ensuring that your vehicle remains in peak condition for years to come.