The Mercedes-Benz CLS C257 is the third generation of one of the most influential four-door coupes ever made. Launched in 2018, it refined the bold formula that the original CLS C219 introduced back in 2004 — blending the practicality of an executive sedan with the visual drama of a coupe. The result is a genuinely striking grand tourer that competes directly with the Audi A7 and BMW 6 Series Gran Turismo.
Built on the MRA platform shared with the W213 E-Class, the C257 benefits from modern engineering, a refined suspension setup, and a fresh lineup of turbocharged engines. It also introduced the new 48V mild-hybrid EQ Boost system to the CLS range for the first time.
For US buyers, the C257 represents a compelling used proposition — sharp looks, strong performance, and a relatively modern feature set. But as with any complex German luxury car, knowing the known weaknesses before signing the check can save you thousands of dollars down the road.
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The CLS C257 entered production in 2018 and remained in production through 2023, representing the third generation of the CLS nameplate. It was initially offered in coupe body style only — Mercedes dropped the Shooting Brake variant for this generation in most markets.
Engine options spanned from efficient four-cylinder mild-hybrids to potent twin-turbocharged V8 AMG variants. The lineup was gradually refined, with the AMG CLS 53 arriving as the performance flagship, while diesel variants (sold in Europe) rounded out the range. The C257 received a mild facelift in 2021, bringing revised lighting signatures and updated infotainment.
| Engine | Displacement | Power | Torque | 0-60 mph | Notes |
|---|---|---|---|---|---|
| CLS 350 (M264) | 2.0L I4 Turbo | 299 hp | 295 lb-ft | 5.9 sec | EQ Boost 48V mild-hybrid |
| CLS 450 (M276) | 3.0L I6 Turbo | 362 hp | 369 lb-ft | 4.8 sec | EQ Boost 48V mild-hybrid |
| CLS 53 AMG (M256) | 3.0L I6 Turbo | 429 hp | 384 lb-ft | 4.4 sec | EQ Boost 48V + electric compressor |
| CLS 220d (OM654) | 2.0L I4 Diesel | 194 hp | 295 lb-ft | 7.5 sec | Europe only |
| CLS 300d (OM656) | 3.0L I6 Diesel | 265 hp | 442 lb-ft | 5.8 sec | Europe only |
| CLS 400d (OM656) | 3.0L I6 Diesel | 340 hp | 516 lb-ft | 4.8 sec | Europe only |
How to Check a Used Mercedes-Benz CLS C257's History
Before buying a used Mercedes-Benz CLS C257, it is essential to ensure full transparency about its past. Undisclosed accidents can hide poor-quality repairs that directly compromise the safety of the driver and passengers.
The C257's aluminum-intensive body structure and complex driver assistance systems make hidden damage especially dangerous. A previously repaired front or rear impact may have left misaligned bodywork panels, unreplaced side curtain or knee airbags, or hastily repaired air suspension components that show no obvious signs of damage to the untrained eye. The AIRMATIC suspension system in particular is expensive to repair properly — a botched fix after an accident can leave the vehicle with uneven ride height and compromised handling. It is therefore strongly recommended to check the vehicle's complete history using its license plate or VIN number before making any purchase decision.
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Key Strengths
The CLS C257 is one of the most well-rounded used luxury coupes available in its price range. Its MRA platform provides a genuinely sorted and composed driving experience, with precise steering and a well-damped ride — especially when equipped with AIRMATIC adaptive suspension.
The nine-speed 9G-Tronic automatic gearbox is smooth and intelligent in everyday driving, while the EQ Boost mild-hybrid system reduces fuel consumption noticeably in traffic. The CLS 450 in particular strikes an excellent balance between refinement and performance, offering 362 hp with strong real-world efficiency.
Interior quality is a genuine high point. The MBUX infotainment system introduced on this generation is intuitive, responsive, and well-integrated. The dual 12.3-inch display setup feels premium even by today's standards.
Parts availability is solid thanks to shared components with the W213 E-Class, which keeps maintenance and repair costs more manageable than a fully bespoke platform would. For a grand tourer of this caliber, the C257 is a relatively practical ownership proposition.
Known Reliability Issues
CLS 350 — M264 (2.0L I4 Turbo + EQ Boost)
Oil consumption and timing chain wear The M264 four-cylinder is known to consume oil more than expected, particularly on higher-mileage examples. The timing chain tensioner can also show early wear, leading to rattling on cold starts. Severity: Moderate. Typically appears from 40,000–60,000 miles.
EQ Boost belt-starter-generator (BSG) issues The 48V mild-hybrid BSG unit can fail prematurely, causing loss of the boost function and triggering warning lights. Replacement is costly, often running $1,500–$2,500 in parts and labor. Severity: Moderate. Appears from 50,000 miles onward.
Water pump and thermostat failures The electric water pump and integrated thermostat assembly are known weak points. Failure causes overheating warnings and loss of cabin heat. Severity: Critical if ignored. Common from 50,000–70,000 miles.
CLS 450 — M276 (3.0L I6 Turbo + EQ Boost)
The M276 is generally considered the most reliable engine in the C257 range. However, some issues remain worth monitoring. For a deeper look at this engine's characteristics, see our Mercedes-Benz M276 Engine Guide.
EQ Boost 48V system faults As with the four-cylinder, the mild-hybrid system's BSG unit and 48V battery can develop faults, especially in climates with extreme temperature swings. Warning lights related to the EQ system are among the most commonly reported issues. Severity: Moderate. Appears from 40,000–60,000 miles.
Camshaft adjuster and oil pressure faults Some owners report oil pressure warning lights linked to the camshaft adjuster solenoid valves becoming clogged with sludge. Using the correct low-viscosity oil and adhering to oil change intervals is critical. Severity: Moderate. Appears from 50,000 miles onward.
Turbocharger boost pressure irregularities Boost pressure inconsistencies, sometimes accompanied by hesitation or a check engine light, have been reported. Often traced to a leaking charge air hose or a failing diverter valve. Severity: Minor to Moderate. Appears from 60,000–80,000 miles.
CLS 53 AMG — M256 (3.0L I6 Turbo + Electric Compressor)
The M256 is an advanced but complex unit. Its combination of a turbocharger, electric supercharger, and 48V mild-hybrid system introduces multiple potential failure points. For a full breakdown, refer to our Mercedes-Benz M256 Engine Guide.
Electric supercharger (EPC) failures The electric pre-turbo compressor is unique to this engine family and expensive to replace. Units can fail with little warning, causing a noticeable drop in low-end response. Severity: Critical. Parts alone can exceed $3,000. Appears from 60,000 miles onward.
48V lithium battery degradation The 48V lithium-ion battery loses capacity over time and in extreme temperatures. A degraded battery reduces EQ Boost availability and can trigger system faults. Severity: Moderate. Typically apparent after 5–7 years of ownership.
Oil leaks from valve cover and front cover gaskets Common on higher-mileage M256 units. Small seepage can accumulate and cause smoke at operating temperature. Severity: Minor to Moderate. Appears from 60,000–80,000 miles.
Chassis Issues
AIRMATIC air suspension leaks and compressor wear The AIRMATIC adaptive air suspension is standard or optional across the C257 range. Air strut leaks and compressor pump failure are the most common chassis-related issues. Symptoms include a sagging ride height on one corner, extended leveling times, or a loud compressor noise at startup. Severity: Moderate to Critical. Appears from 60,000–100,000 miles. Compressor replacement averages $800–$1,500.
Front control arm and bushing wear The front control arm bushings degrade with normal use and are a standard wear item. Worn bushings cause vague steering, clunking over bumps, and uneven tire wear. Severity: Minor. Typically requires attention from 50,000–70,000 miles.
Electronics and Software
MBUX infotainment freezes and reboot loops Early production C257 units (2018–2019) occasionally suffered from MBUX software instability, including screen freezes and spontaneous reboots. Most issues were resolved via dealer software updates. Severity: Minor. Primarily affects pre-facelift models.
Driver assistance system calibration faults The suite of radar and camera-based driver assistance systems is sensitive to even minor body repairs. Radar sensor misalignment and camera calibration errors are common after front-end work. Severity: Moderate. Can be triggered at any mileage following a repair.
Instrument cluster and ambient lighting module faults Some owners report intermittent failures in the digital instrument cluster or ambient lighting strips. Often caused by a failing control module rather than the display itself. Severity: Minor. Appears from 40,000 miles onward.
Maintenance and Servicing
The CLS C257 follows Mercedes-Benz's ASSYST Plus adaptive service system, which monitors driving conditions and calculates oil change intervals accordingly. In practice, plan on oil changes every 10,000 miles or annually, whichever comes first.
Recommended service intervals: - Engine oil and filter: every 10,000 miles - Spark plugs: every 30,000–40,000 miles (four-cylinder) or 40,000–60,000 miles (six-cylinder) - Transmission fluid (9G-Tronic): every 40,000 miles — Mercedes calls it lifetime fill, but regular changes prevent wear - Brake fluid: every 2 years - Air filter: every 20,000–30,000 miles - AIRMATIC filter/dryer: inspect every 40,000 miles
Average service costs in the US: - Basic oil service: $200–$350 at an independent specialist - Major service (filters, plugs, fluid refresh): $600–$1,000 - AIRMATIC compressor replacement: $800–$1,500 - Transmission fluid service: $250–$400
Sticking strictly to oil change intervals is especially important on the M264 and M256 engines, where sludge buildup accelerates timing chain and camshaft adjuster wear significantly.
Parts to Watch / Replace First
Air suspension struts — All four struts should be inspected on any C257 over 80,000 miles. Front struts wear faster than rear units. Replace in axle pairs.
EQ Boost belt-starter-generator — A known wear item on both the M264 and M276. Check for hesitation during the EQ Boost engagement phase and scan for 48V system fault codes.
Timing chain tensioner (M264) — Listen for cold-start rattle on four-cylinder models. Early replacement is cheaper than dealing with a stretched chain.
Electric water pump — The electric pump assembly on the four-cylinder engine is a high-failure-rate component. Any overheating warning should prompt immediate inspection.
Control arm bushings — Standard front-end wear item. Inspect for cracking or excessive play at every tire rotation.
Camshaft adjuster solenoids — On the M276 and M256 engines, these solenoids are prone to clogging. A simple cleaning or replacement can prevent serious engine faults.
9G-Tronic transmission pan gasket and filter — If the transmission has not had a fluid service, prioritize this. A neglected unit can develop shudder or hesitation on shifts after 70,000 miles.
Brake pad wear sensors — Frequently overlooked. The C257's brake system is aggressive and sensors are inexpensive insurance against rotor damage.
FAQ
Is the Mercedes-Benz CLS C257 reliable?
The CLS C257 is moderately reliable for a luxury grand tourer of its complexity. The CLS 450 with the M276 engine is the most dependable variant. The four-cylinder and AMG 53 models carry more risk due to their more complex mild-hybrid systems.
What is the best engine option in the CLS C257?
The CLS 450 with the M276 3.0L inline-six is widely regarded as the sweet spot. It offers strong performance, good refinement, and a proven engine architecture. The AMG CLS 53 is more exciting but significantly more expensive to maintain.
How many miles will a CLS C257 last?
A well-maintained CLS C257 can comfortably reach 150,000–200,000 miles. The key variables are adherence to oil change intervals, timely AIRMATIC maintenance, and addressing any EQ Boost system faults before they cascade into larger problems.
Is the CLS C257 expensive to maintain?
Yes, relative to mainstream vehicles. Expect to budget $1,500–$3,000 per year for routine maintenance and wear items. Unplanned repairs — particularly involving the air suspension, BSG unit, or driver assistance systems — can push annual costs significantly higher.
What should I check when buying a used CLS C257?
Prioritize a full OBD diagnostic scan for stored and pending fault codes, especially in the 48V EQ Boost system. Inspect the AIRMATIC suspension for leaks and uneven ride height. Verify the service history to confirm oil change compliance. Ask about any previous accident or calibration work on driver assistance sensors.
Are parts easy to find for the CLS C257?
Yes. The C257 shares a large portion of its mechanical and electrical components with the W213 E-Class, which means strong aftermarket and OEM parts availability. Specialist suppliers offer competitive pricing compared to Mercedes-Benz main dealers.
Which model years of the CLS C257 are the most reliable?
The 2021 facelift and later models tend to be more reliable, as Mercedes addressed the early MBUX software instability and made incremental improvements to the mild-hybrid system. Pre-facelift 2018–2019 cars carry slightly more risk of early software and 48V system issues.
Conclusion
The Mercedes-Benz CLS C257 earns a reliability score of 6.5/10 — above average for the segment, but not without significant maintenance demands. The CLS 450 stands out as the most sensible used buy, combining a proven engine with the model's best qualities. Budget carefully for the air suspension and mild-hybrid system, keep up with oil changes, and the C257 will reward you with one of the most visually and dynamically satisfying ownership experiences in the luxury coupe market. Browse our catalog for quality replacement parts for the CLS C257 to keep yours running at its best.