The Mercedes-Benz S-Class W222 S 450 represents a perfect blend of luxury, innovation, and performance. Featuring a powerful 3.0L turbocharged V6 engine with a mild hybrid EQ Boost system, the S 450 is designed for effortless acceleration, supreme comfort, and cutting-edge technology. However, like all high-end vehicles, it is not immune to mechanical, electrical, and reliability concerns.
Whether you are an existing owner or considering purchasing a used Mercedes S 450, being aware of common problems can help you maintain the car effectively and avoid expensive repairs. This in-depth guide explores the most frequently reported issues with the W222 S 450, their causes, symptoms, and possible solutions.
Mercedes S-Class W222 S 450 Engine and Performance Issues
The heart of the Mercedes S 450 is its M256 3.0L inline-six turbocharged engine, which is paired with a 48V mild-hybrid system for enhanced efficiency and performance. While this setup offers a smooth and powerful driving experience, certain engine-related issues have been reported by owners.
Turbocharger and Boost System Failures
The turbocharger in the S 450 provides additional power by compressing air into the engine, but it is prone to failure due to excessive carbon buildup, oil contamination, or actuator malfunctions. If the turbocharger starts to fail, you may notice a loss of power, excessive exhaust smoke, and a whining noise from the engine bay.
Another potential issue is a malfunction in the electronic wastegate actuator, which controls turbo boost pressure. If this component fails, it can cause erratic power delivery, reduced acceleration, or even put the vehicle into limp mode. Regular oil changes using high-quality synthetic oil and periodic intake system cleaning can help prevent carbon buildup, which is a major contributor to turbo issues.
Mild Hybrid EQ Boost System Malfunctions
One of the standout features of the S 450 is its mild-hybrid EQ Boost system, which uses a 48V electrical system to provide extra torque during acceleration and improve fuel efficiency. However, owners have reported problems such as the hybrid battery failing prematurely or the system triggering warning lights related to the electrical boost.
Common symptoms include a sudden loss of power assist, warning messages on the dashboard, and erratic start/stop system behavior. In many cases, software updates or a battery replacement can resolve the issue. However, if the mild-hybrid motor fails, it can be an expensive repair.
Oil Leaks and Excessive Oil Consumption
Like many turbocharged engines, the M256 engine in the S 450 has been reported to consume more oil than expected. Some owners have noticed that they need to top up oil between service intervals, which may be caused by worn valve cover gaskets, oil cooler leaks, or degraded piston rings.
Oil leaks are also common around the timing chain cover and turbo oil feed lines. If left unchecked, oil leaks can lead to reduced lubrication, increased engine wear, and even potential engine failure. Regularly checking oil levels and addressing leaks early can prevent costly repairs.
Mercedes S-Class W222 S 450 Transmission Problems
The S 450 comes equipped with the 9G-Tronic (9-speed automatic) transmission, known for its smooth shifting and efficiency. However, some owners have encountered transmission-related issues that affect drivability and performance.
Hard Shifting and Gear Slippage
One of the most common complaints is rough or delayed shifting. Symptoms include jerky gear changes, hesitation during acceleration, and sudden shifts when decelerating. This issue is often linked to degraded transmission fluid, software calibration problems, or excessive wear in the valve body.
Regular transmission fluid changes (recommended every 60,000 km) can help maintain smooth shifting. If issues persist, a software update or reprogramming of the transmission control module (TCM) may be required. In some cases, a faulty torque converter can also contribute to shifting problems.
Transmission Overheating
Since the 9G-Tronic transmission is highly efficient, it requires a proper cooling system to prevent overheating. Some S 450 models have experienced transmission overheating due to faulty cooling lines or transmission oil cooler failures. Symptoms include warning lights on the dashboard, erratic shifting, and a burning smell.
Regularly inspecting the transmission cooler and ensuring proper fluid levels can prevent overheating issues. If the problem persists, replacing the transmission oil cooler or repairing the cooling lines may be necessary.
Mercedes S-Class W222 S 450 Suspension and Ride Quality Problems
The Mercedes S-Class is praised for its comfortable ride, thanks to its advanced AIRMATIC air suspension. However, suspension-related failures can affect the overall driving experience and lead to costly repairs.
AIRMATIC Suspension Leaks and Compressor Failures
The AIRMATIC air suspension system in the S 450 is designed to adapt to different driving conditions by adjusting ride height and damping. Over time, the air struts can develop leaks, causing the car to sag or sit unevenly. A common symptom is the car sitting lower than normal, especially after being parked overnight.
A failing air compressor is another common issue, often caused by excessive strain due to air leaks. If the compressor fails, the suspension may stop adjusting altogether, leading to a bumpy and uncomfortable ride. Replacing air struts early and ensuring that there are no leaks in the system can help prolong the lifespan of the compressor.
Control Arm and Bushing Wear
Over time, the control arm bushings in the suspension system can degrade, leading to increased road vibrations, poor handling, and knocking sounds when driving over bumps. This is particularly noticeable in high-mileage vehicles. Replacing worn bushings and control arms can restore ride quality and improve steering precision.
Mercedes S-Class W222 S 450 Electrical and Infotainment System Problems
As a luxury vehicle, the S 450 is packed with advanced electronics and an extensive infotainment system. However, electrical issues can be particularly frustrating due to their complexity.
COMAND System and Infotainment Malfunctions
Many owners have reported problems with the COMAND infotainment system, including system freezes, unresponsive controls, and software glitches. In some cases, the system may randomly restart or fail to connect to Bluetooth devices.
Software updates and a hard reset can often resolve these issues. However, if the problem persists, replacing the multimedia control module may be necessary.
Keyless-Go and Electronic Door Handle Failures
The Keyless-Go system allows for keyless entry and push-button start, but some owners have encountered issues where the system fails to recognize the key fob. This can be due to a weak battery in the key fob, a faulty receiver module, or signal interference.
Additionally, the electronic door handles in the S-Class can sometimes fail, either retracting improperly or not responding to touch. This issue is often caused by faulty wiring inside the handles, requiring replacement of the affected components.
Battery Drain Issues
Battery drain is a common issue in the S 450, particularly in models with extensive electronic features. Owners have reported instances where the car’s 12V battery depletes quickly, causing issues such as difficulty starting the vehicle or triggering warning lights.
Possible causes include a weak alternator, excessive power draw from parked electronic systems, or a failing auxiliary battery (used in the mild-hybrid system). Performing a battery test and checking for parasitic drains can help diagnose and fix the issue.
Mercedes S-Class W222 S 450 Cooling System and Overheating Problems
Maintaining the optimal engine temperature is crucial for the longevity and performance of the Mercedes S 450. However, certain cooling system components are known to develop issues over time, leading to overheating and potential engine damage.
Radiator and Coolant Hose Leaks
One of the most common cooling system failures in the W222 S 450 is radiator and coolant hose leaks. The cooling system operates under high pressure, and over time, rubber hoses and plastic components can degrade, leading to coolant leaks.
Symptoms of a coolant leak include low coolant levels, puddles under the car, and increased engine temperatures. If left unchecked, coolant leaks can lead to overheating, which may cause severe engine damage. Regular inspection of the cooling system and replacing worn-out hoses and radiator components can prevent such issues.
Water Pump and Thermostat Failures
The water pump circulates coolant through the engine to regulate temperature, while the thermostat controls the flow of coolant based on engine heat. A failing water pump can cause insufficient coolant circulation, leading to overheating. Similarly, a malfunctioning thermostat can get stuck in the open or closed position, disrupting the cooling system.
Symptoms include erratic temperature gauge readings, loss of heater function, and engine overheating warnings. Replacing the water pump and thermostat at the first sign of failure can prevent more severe cooling system problems.
Mercedes S-Class W222 S 450 Braking System Issues
The braking system in the Mercedes S 450 is designed for maximum safety and performance, but some owners have reported premature wear and electronic brake system malfunctions.
Excessive Brake Pad and Rotor Wear
Due to the weight of the S 450 and its powerful braking system, brake pads and rotors tend to wear out faster than expected. Drivers may experience symptoms such as squealing noises, vibrations in the brake pedal, and longer stopping distances.
Regularly inspecting brake components and replacing them as needed ensures optimal braking performance. Using high-quality brake pads can also help extend the lifespan of the braking system.
Brake System Warning Lights
Some owners have encountered random brake system warning messages, often triggered by faulty brake sensors or electronic stability control (ESC) module issues. If the brake warning light appears, it’s crucial to have the vehicle diagnosed using a professional scanner to pinpoint the cause. In some cases, software updates or sensor replacements can resolve the issue.
Mercedes S-Class W222 S 450 Interior Wear and Comfort Issues
The Mercedes S 450 offers one of the most luxurious cabins in its class, but with time, certain components may wear out or develop issues that impact comfort and convenience.
Seat Bolster and Leather Wear
Frequent use of the driver's seat can lead to premature wear on the leather upholstery and seat bolsters. The constant pressure from entering and exiting the vehicle causes creases, cracks, and fading, particularly in high-mileage models.
Regularly treating the leather with high-quality conditioners can help preserve its appearance and durability. For severe wear, reupholstering or using seat covers may be necessary.
Climate Control Malfunctions
The advanced climate control system in the S 450 is designed for optimal comfort, but issues such as weak airflow, inconsistent cooling, or complete AC failure can occur. Common causes include clogged cabin air filters, low refrigerant levels, 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 underlying issue.
Mercedes S-Class W222 S 450 Fuel System and Injector Problems
The direct fuel injection system in the S 450 offers improved efficiency and performance, but it can develop problems over time, leading to reduced fuel economy and performance issues.
High-Pressure Fuel Pump Failure
The high-pressure fuel pump (HPFP) delivers fuel to the engine at the necessary pressure. If the HPFP starts to fail, symptoms such as rough idling, sluggish acceleration, and difficulty starting the vehicle may arise. In extreme cases, the engine may stall due to fuel starvation.
Replacing a faulty fuel pump promptly can prevent further engine damage. Using high-quality fuel and periodic injector cleaning can also help maintain fuel system efficiency.
Carbon Buildup in Fuel Injectors
Over time, carbon deposits can accumulate on the fuel injectors, leading to inefficient fuel combustion. Symptoms include misfires, rough idling, and increased fuel consumption. Professional fuel injector cleaning or replacement may be required to restore optimal performance.
Mercedes S-Class W222 S 450 Exhaust System and Emission Control Issues
The Mercedes S 450 is equipped with an advanced exhaust system designed to meet strict emissions regulations. However, components such as the catalytic converter, oxygen sensors, and particulate filters can develop issues over time.
Catalytic Converter Clogging
A failing catalytic converter can cause reduced engine performance, increased emissions, and a check engine light. This issue is often caused by excessive carbon buildup, unburned fuel, or prolonged driving with a misfiring engine.
If the catalytic converter becomes clogged, it may need to be replaced to restore proper engine function and emissions compliance.
Oxygen Sensor Malfunctions
Oxygen sensors play a crucial role in regulating fuel mixture and emissions. If an oxygen sensor fails, the vehicle may experience poor fuel efficiency, increased emissions, and rough engine performance. Replacing faulty oxygen sensors can help maintain fuel efficiency and reduce emissions.
Mercedes S-Class W222 S 450 Long-Term Maintenance and Ownership Considerations
Owning a high-end vehicle like the Mercedes S 450 requires regular maintenance and attention to detail to prevent costly repairs and ensure long-term reliability.
Regular Maintenance is Key
Routine oil changes, transmission fluid changes, brake inspections, and suspension checks are crucial for keeping the S 450 running smoothly. Using manufacturer-recommended fluids and components can help extend the lifespan of key systems.
Software Updates and Recalls
Mercedes-Benz frequently releases software updates to address performance issues and fix bugs in the vehicle’s electronics. Keeping your car updated with the latest software can resolve minor glitches and enhance overall performance. Checking for recalls can also help identify factory defects that may require repairs.
Conclusion
The Mercedes-Benz S-Class W222 S 450 is an exceptional luxury sedan with cutting-edge technology, smooth performance, and a refined driving experience. However, like any vehicle, it comes with its share of common issues, including turbocharger failures, transmission shifting problems, AIRMATIC suspension leaks, electrical glitches, and excessive brake wear.
By staying informed about potential issues and performing regular maintenance, owners can prevent major breakdowns and costly repairs. Proactively addressing problems and using high-quality replacement parts can help ensure that your S 450 remains in peak condition for years to come.
For expert Mercedes-Benz repairs and servicing, visit European Auto Pro 253 Goodwood Road, Kings Park, 5034 South Australia. Our professional technicians specialize in diagnosing and fixing common S 450 issues, ensuring your luxury vehicle continues to perform at its best.