2001-2025 Mercedes-Benz C-Class Problems: 12 Issues Every Owner Should Know

2001-2025 model years · 11,200+ owner reports · Updated May 2026

According to Au7o's analysis of 11,200+ owner reports, the 2001-2025 Mercedes-Benz C-Class has 12 documented known issues, with 6 rated critical. The most serious are SAM Module Failure ($600-$1,800 repair), 7G-Tronic Valve Body Failure ($800-$3,000 repair), W204 Rear Subframe Cracking ($500-$4,000 repair), Front Seat Occupant Classification / Passenger Airbag Warning Faults ($300-$2,500 repair), 48V Mild-Hybrid / Integrated Starter-Generator Failure Causing No-Start and Power Loss ($500-$6,000 repair) and MBUX / Instrument Cluster Black Screen, Rebooting, or No Rear Camera Image ($0-$2,500 repair). The most commonly reported issue is SAM Module Failure with 2,500 owner reports. Across all issues, repair costs range from $50 to $6,000. DIY maintenance guides at au7o.io.

All 12 Known Issues

When Issues Typically Appear

Front Seat Occupant Classification / Passenger Airbag Warning Faults

0K-30K

48V Mild-Hybrid / Integrated Starter-Generator Failure Causing No-Start and Power Loss

0K-40K

MBUX / Instrument Cluster Black Screen, Rebooting, or No Rear Camera Image

0K-30K

Driver Assistance Sensor Misalignment Causing 'Inoperative' Warnings and Disabled Features

0K-50K

Premature Front Brake Squeal, Judder, and Rotor/Pads Replacement

3K-30K

Sunroof Drain Clog Water Damage

30K-100K

M274 Turbo Wastegate Rattle

30K-80K

SAM Module Failure

50K-120K

Cam Adjuster Solenoid Failure

50K-100K

W204 Rear Subframe Cracking

60K-120K

Door Lock Actuator Failure

60K-130K

7G-Tronic Valve Body Failure

70K-130K

038K75K113K150K mi

Community Reported

2,500 owners

On the 2001-2007 Mercedes-Benz C-Class, the Signal Acquisition Module (SAM) — essentially the fuse box and body control module — fails due to water intrusion or internal solder joint cracking. Causes erratic electrical behavior including lights, wipers, and windows malfunctioning.

This issue also affects: Volvo XC90, Chrysler Crossfire, Jaguar S-TYPE

Common Symptoms

Random electrical malfunctions
Wipers or lights operate on their own

How to Fix

Replace the failed SAM module (front or rear depending on symptoms). Requires dealer-level programming to code the new unit to the vehicle. Check for water leaks at the windshield cowl area that may have caused the failure.

What Owners Are Using

Parts and tips from 2,500+ owners who fixed this issue

TipBefore replacing the SAM, check for water intrusion from clogged cowl drains. Fixing the drain leak prevents repeat SAM failures.

Typical repair cost:$600 - $1,800

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2,500+ owners have reported this issue

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Community Reported

High Confidence2,500 reportsLast reported by owners Mar 2025Reviewed Mar 2026

On the 2022-2025 Mercedes-Benz C-Class 2.0L turbo mild-hybrid I4 (C300/C300 4MATIC), the W206 C-Class uses a 48V mild-hybrid system with an integrated starter-generator (ISG), and owners have reported no-start conditions, repeated warning messages, charging-system faults, and sudden reduced-power events tied to the 48V system. Mercedes has issued service information and field actions on related hybrid electrical faults across current models using this architecture, and owner complaints describe vehicles becoming undriveable or requiring towing. Failures can involve the ISG itself, DC/DC conversion, wiring, or software/calibration issues that trigger shutdowns and battery warnings.

This issue also affects: Alfa Romeo Tonale, Audi A6 allroad, Land Rover Range Rover Sport

Common Symptoms

vehicle will not start
48V battery warning
check engine light
reduced power
charging system malfunction message
engine shuts off or will not restart after auto stop/start
vehicle requires towing

How to Fix

A proper diagnosis requires scanning both the 48V and 12V systems, checking state of charge, converter operation, and fault history in the powertrain and hybrid control modules. Repairs may include software updates, replacement of the integrated starter-generator or associated power electronics, and battery/module adaptation after installation. Because the system is high-current and model-specific, independent repair options are limited compared with dealer service.

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipIf a no-start follows auto stop/start or a 48V warning, have the vehicle scanned before repeated jump-start attempts; repeated low-voltage events can muddy the root cause.
TipOwners often recommend keeping copies of all warning-message photos and tow invoices because intermittent 48V faults may require multiple dealer visits.

Typical repair cost:$500 - $6,000

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Community Reported

High Confidence0 reportsLast reported by owners Invalid DateReviewed Invalid Date

On the 2022-2025 Mercedes-Benz C-Class, owners of the W206 C-Class have reported intermittent or persistent failures of the central MBUX display and digital instrument cluster, including black screens, repeated rebooting, frozen infotainment, and loss of the rear-view camera image. This is well documented through NHTSA complaints and Mercedes service communications tied to software faults and control-unit communication problems on the new electrical architecture. When the display or camera feed drops out, key vehicle information and driver-assistance functions may also be unavailable until the system is restarted or reprogrammed.

This issue also affects: Mercedes-Benz AMG GT, Mercedes-Benz CLS-Class, Mercedes-Benz E-Class

Common Symptoms

center screen goes black
instrument cluster blank or rebooting
rear-view camera unavailable
frozen infotainment
warning messages for inoperative assistance systems
loss of navigation or audio controls

How to Fix

Diagnosis typically starts with a full vehicle scan for communication faults in the infotainment, camera, and central gateway modules, followed by checking software level and 12V system health. Mercedes repairs commonly involve software updates/reprogramming of MBUX-related control units, replacement of a faulty display/control module if updates do not hold, and verification of camera operation after coding. If symptoms are intermittent, documenting exact conditions and preserving fault logs helps the dealer reproduce the issue.

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipBefore dealer visits, record a video of the screen rebooting or camera failing; intermittent MBUX faults are easier to warranty if the symptom is documented.
TipAsk the dealer to verify all infotainment and camera control units are on the latest software integration level, not just perform a battery reset.
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Typical repair cost:$0 - $2,500

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Community Reported

High Confidence0 reportsLast reported by owners Invalid DateReviewed Invalid Date

Community Reported

1,100 owners

On the 2008-2018 Mercedes-Benz C-Class, the door lock actuators fail, preventing doors from locking or unlocking via the remote or interior switches. The actuator motor wears out or the internal mechanism jams, commonly on the driver door first.

This issue also affects: Audi Q8 e-tron, Chrysler Pacifica, Chrysler Town & Country

Common Symptoms

Door does not lock or unlock with remote
Clicking noise from door but no latch movement

How to Fix

Replace the failed door lock actuator. Requires removing the door panel. OEM actuators are recommended for longevity; aftermarket units tend to fail within 1-2 years.

What Owners Are Using

Parts and tips from 1,100+ owners who fixed this issue

TipUse OEM or Genuine Mercedes door lock actuators only. Cheap aftermarket units are the #1 complained-about replacement part on MBWorld forums.

Typical repair cost:$150 - $500

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Community Reported

Medium Confidence1,100 reportsLast reported by owners Jul 2025Reviewed Mar 2026

On the 2022-2025 Mercedes-Benz C-Class, multiple W206 owners have reported passenger restraint warnings, inoperative passenger airbag indicators, and seat-related fault messages shortly after purchase. These complaints align with Mercedes service actions and owner reports involving seat occupancy detection mats/sensors, seat wiring, or control-module calibration issues. Because the system determines passenger airbag deployment logic, faults can trigger warning lights and require immediate diagnosis.

This issue also affects: Jeep Grand Cherokee, Lexus LX, Nissan Altima

Common Symptoms

passenger airbag warning
restraint system malfunction
occupant classification inoperative
airbag light illuminated
warning chime on startup

How to Fix

Diagnosis should include scanning the supplemental restraint system for seat-occupancy and seat-module faults, inspecting under-seat connectors/wiring, and checking for applicable software updates or service campaigns. Repairs may involve recalibration, harness repair, or replacement of the seat occupancy sensor/mat or related control unit. After repair, the restraint system should be rescanned and the passenger airbag status verified with different seat loads.

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipDo not ignore intermittent passenger airbag warnings; owners recommend getting a fault printout while the issue is active because some seat-sensor faults self-clear.
TipCheck for items pressing on or under the passenger seat before service, but if warnings persist, insist on SRS-specific diagnosis rather than a generic code scan.

Typical repair cost:$300 - $2,500

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Community Reported

High Confidence0 reportsLast reported by owners Invalid DateReviewed Invalid Date

On the 2022-2025 Mercedes-Benz C-Class, owners of 2022-2025 C-Class cars frequently report sudden warnings that Active Brake Assist, Distronic, lane-keeping, blind-spot monitoring, or parking sensors are inoperative. On the W206, these faults are often tied to radar/camera calibration sensitivity, software issues, or sensor obstruction/misalignment after minor impacts, windshield work, or even routine driving in poor weather. The result is a cluster of driver-assistance features dropping offline until the system is recalibrated or updated.

This issue also affects: Hyundai Sonata, Kia Rio, Hyundai Veloster

Common Symptoms

Active Brake Assist inoperative
blind spot assist unavailable
lane keeping assist unavailable
parking sensors unavailable
adaptive cruise disabled
multiple driver assistance warnings at once

How to Fix

The vehicle should be scanned for camera, radar, and ADAS communication faults, then inspected for dirty sensor faces, bumper damage, windshield replacement history, and alignment issues. Many cases are resolved with software updates and static/dynamic calibration of the front camera or radar sensors; damaged brackets or sensors must be replaced before calibration. Battery voltage should also be verified because low voltage can trigger multiple false ADAS warnings.

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipAfter windshield replacement or front-end repair, owners recommend confirming that ADAS calibration was actually performed, not just sensor installation.
TipKeep radar covers and camera areas clean, but if warnings recur in clear weather, request a calibration report and software version printout from the dealer.

Typical repair cost:$150 - $2,200

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Community Reported

Medium Confidence0 reportsLast reported by owners Invalid DateReviewed Invalid Date

Community Reported

2,200 owners

On the 2005-2013 Mercedes-Benz C-Class, the 722.9 7G-Tronic automatic transmission develops valve body issues causing harsh or delayed shifts, particularly the 2-3 and 4-5 upshifts. The conductor plate (electrical connector inside the valve body) is also failure-prone.

This issue also affects: Chrysler LeBaron, Dodge Avenger, GMC Sierra 3500HD

Common Symptoms

Harsh or jerky shifting
Delayed engagement when shifting from P to D

How to Fix

Replace the valve body or have it rebuilt by a Mercedes transmission specialist. Replace the conductor plate and speed sensors at the same time. A full transmission fluid and filter service may temporarily improve symptoms.

What Owners Are Using

Parts and tips from 2,200+ owners who fixed this issue

TipChange the transmission fluid and filter every 40,000 miles. Mercedes calls it a "lifetime fill" but regular service dramatically extends valve body life.

Typical repair cost:$800 - $3,000

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2,200+ owners have reported this issue

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Community Reported

High Confidence2,200 reportsLast reported by owners Jun 2025Reviewed Mar 2026

Community Reported

900 owners

On the 2008-2014 Mercedes-Benz C-Class, the W204 C-Class rear subframe develops stress cracks at the mounting points, particularly on vehicles driven on rough roads or in cold climates. Cracks compromise rear suspension geometry and handling stability.

This issue also affects: Mercedes-Benz SLK-Class

Common Symptoms

Clunking noise from rear over bumps
Rear end feels loose or unstable

How to Fix

Inspect the rear subframe for cracks at each service. Weld-repair minor cracks or replace the subframe entirely for severe damage. Mercedes issued a service campaign for some VINs.

What Owners Are Using

Parts and tips from 900+ owners who fixed this issue

NoteHave the subframe inspected at every alignment. Cracks start small and grow quickly. Catching them early means a $500 weld vs. a $4,000 subframe replacement.

Typical repair cost:$500 - $4,000

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900+ owners have reported this issue

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Community Reported

Medium Confidence900 reportsLast reported by owners Apr 2025Reviewed Mar 2026

Community Reported

1,500 owners

On the 2015-2021 Mercedes-Benz C-Class 2.0L M274 Turbo, the M274 2.0L turbo engine develops an audible wastegate rattle at idle and low RPM due to wear in the wastegate actuator linkage. While not immediately dangerous, it worsens over time and can eventually affect boost control.

This issue also affects: Audi A3, Audi A6, Audi A8

Common Symptoms

Rattling noise at idle from turbo area
Rattle worsens in cold weather

How to Fix

Replace the turbocharger wastegate actuator or the complete turbo assembly if linkage is excessively worn. Some dealers adjust the wastegate arm as a temporary fix.

What Owners Are Using

Parts and tips from 1,500+ owners who fixed this issue

TipIf the rattle is mild and no boost codes are present, monitor it. Many owners live with the noise for years. Only replace if boost control is affected.

Typical repair cost:$400 - $2,500

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High Confidence1,500 reportsLast reported by owners Nov 2025Reviewed Mar 2026

Community Reported

1,200 owners

On the 2012-2018 Mercedes-Benz C-Class, the camshaft adjuster solenoids (VANOS equivalent) stick or fail due to oil varnish buildup, causing rough idle, poor throttle response, and check engine lights. Particularly common with extended oil change intervals.

This issue also affects: Audi A4, Audi A5, Audi A6

Common Symptoms

Rough idle after warm-up
Check engine light with cam timing codes

How to Fix

Replace the camshaft adjuster solenoid(s). Clean the oil passages feeding the solenoids. Use Mercedes-approved 229.51 spec oil and change every 7,500 miles to prevent recurrence.

What Owners Are Using

Parts and tips from 1,200+ owners who fixed this issue

TipShorten oil change intervals to 7,500 miles instead of the Mercedes-recommended 10,000-13,000 miles. Dirty oil is the primary cause of solenoid failure.

Typical repair cost:$200 - $600

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1,200+ owners have reported this issue

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Community Reported

Medium Confidence1,200 reportsLast reported by owners Sep 2025Reviewed Mar 2026

Community Reported

1,800 owners

On the 2008-2020 Mercedes-Benz C-Class, the sunroof drain tubes clog with debris, causing water to back up into the headliner, A-pillars, and footwells. Prolonged leaking damages the SAM module, amplifier, and other electronics mounted under the carpet.

This issue also affects: Ford Escape, Honda Civic, Hyundai Santa Fe

Common Symptoms

Wet headliner or A-pillar trim
Water pooling in footwells after rain

How to Fix

Clear sunroof drain tubes with compressed air or flexible wire from each corner of the sunroof tray. Clean drains preventively twice per year. If electronics are damaged, dry the area thoroughly and test all modules.

What Owners Are Using

Parts and tips from 1,800+ owners who fixed this issue

TipClean sunroof drains every spring and fall. Pour a cup of water in each corner of the open sunroof tray and verify it exits under the car near the wheels.

Typical repair cost:$50 - $2,000

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High Confidence1,800 reportsLast reported by owners Oct 2025Reviewed Mar 2026

On the 2022-2025 Mercedes-Benz C-Class, a recurring owner complaint on the current C-Class is noisy front brakes, vibration under braking, and early rotor/pad replacement despite relatively low mileage. Reports on owner forums and complaint databases describe squeal when cold or at low speed, as well as pulsation or steering-wheel shake from rotor hot spots or uneven pad transfer. The issue appears more common on vehicles used for short trips or with repeated low-speed braking, though some owners report it even with normal driving.

This issue also affects: Audi A4, Mercedes-Benz SL-Class, Volvo XC90

Common Symptoms

front brake squeal
grinding or scraping noise
steering wheel shake when braking
brake pulsation
premature pad wear

How to Fix

Diagnosis should confirm whether the problem is simple pad glazing/noise, rotor thickness variation, or hardware/caliper drag. Repairs range from cleaning and lubricating pad contact points and bedding the brakes properly to replacing front pads and rotors with updated parts if vibration or scoring is present. Wheel torque should be checked after service because uneven torque can worsen brake pulsation.

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipOwners commonly recommend a proper brake bedding procedure after pad/rotor replacement to reduce repeat squeal and uneven pad deposits.
TipIf replacing parts out of warranty, ask for coated OE-equivalent rotors and low-dust pads matched to the car's wear sensors.
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Typical repair cost:$250 - $1,400

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Community Reported

Medium Confidence0 reportsLast reported by owners Invalid DateReviewed Invalid Date

Frequently Asked Questions

What are the most common Mercedes-Benz C-Class problems?

According to Au7o's analysis of 11,200+ owner reports, the 2001-2025 Mercedes-Benz C-Class has 12 documented issues. The most frequently reported are: SAM Module Failure, 7G-Tronic Valve Body Failure, W204 Rear Subframe Cracking. Of these, 6 are rated critical and should be addressed promptly.

Is the Mercedes-Benz C-Class reliable?

The 2001-2025 Mercedes-Benz C-Class has 12 known issues documented across 11,200+ owner reports. 6 issues are rated critical: SAM Module Failure and 7G-Tronic Valve Body Failure and W204 Rear Subframe Cracking and Front Seat Occupant Classification / Passenger Airbag Warning Faults and 48V Mild-Hybrid / Integrated Starter-Generator Failure Causing No-Start and Power Loss and MBUX / Instrument Cluster Black Screen, Rebooting, or No Rear Camera Image. Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.

How much does it cost to fix common Mercedes-Benz C-Class problems?

Repair costs for known Mercedes-Benz C-Class issues range from $0 to $6,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, SAM Module Failure, typically costs $600-$1,800 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.

What year Mercedes-Benz C-Class is the most reliable?

Reliability varies across model years of the Mercedes-Benz C-Class. Based on documented issues, problems are most commonly reported in earlier model years. Au7o recommends checking the specific known issues for your target year before purchasing, and having a pre-purchase inspection performed by a qualified mechanic. Our known issues database covers the 2001-2025 Mercedes-Benz C-Class with 12 documented issues documented across 11,200+ owner reports.

What is the 2001-2007 Mercedes-Benz C-Class SAM Module Failure?

The Signal Acquisition Module (SAM) — essentially the fuse box and body control module — fails due to water intrusion or internal solder joint cracking. Causes erratic electrical behavior including lights, wipers, and windows malfunctioning. Repairs typically run $600-$1,800. Severity: high.

All 12 Known Issues

When Issues Typically Appear

2001-2007 Mercedes-Benz C-Class: SAM Module Failure#

Common Symptoms

How to Fix

What Owners Are Using

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2022-2025 Mercedes-Benz C-Class: 48V Mild-Hybrid / Integrated Starter-Generator Failure Causing No-Start and Power Loss#

Common Symptoms

How to Fix

What Owners Are Using

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2022-2025 Mercedes-Benz C-Class: MBUX / Instrument Cluster Black Screen, Rebooting, or No Rear Camera Image#

Common Symptoms

How to Fix

What Owners Are Using

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2008-2018 Mercedes-Benz C-Class: Door Lock Actuator Failure#

Common Symptoms

How to Fix

What Owners Are Using

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2022-2025 Mercedes-Benz C-Class: Front Seat Occupant Classification / Passenger Airbag Warning Faults#

Common Symptoms

How to Fix

What Owners Are Using

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2022-2025 Mercedes-Benz C-Class: Driver Assistance Sensor Misalignment Causing 'Inoperative' Warnings and Disabled Features#

Common Symptoms

How to Fix

What Owners Are Using

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2005-2013 Mercedes-Benz C-Class: 7G-Tronic Valve Body Failure#

Common Symptoms

How to Fix

What Owners Are Using

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2008-2014 Mercedes-Benz C-Class: W204 Rear Subframe Cracking#

Common Symptoms

How to Fix

What Owners Are Using

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2015-2021 Mercedes-Benz C-Class: M274 Turbo Wastegate Rattle#

Common Symptoms

How to Fix

What Owners Are Using

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2012-2018 Mercedes-Benz C-Class: Cam Adjuster Solenoid Failure#

Common Symptoms

How to Fix

What Owners Are Using

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2008-2020 Mercedes-Benz C-Class: Sunroof Drain Clog Water Damage#

Common Symptoms

How to Fix

What Owners Are Using

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2022-2025 Mercedes-Benz C-Class: Premature Front Brake Squeal, Judder, and Rotor/Pads Replacement#

Common Symptoms

How to Fix

What Owners Are Using

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Other Mercedes-Benz Models

Frequently Asked Questions

What are the most common Mercedes-Benz C-Class problems?

Is the Mercedes-Benz C-Class reliable?

How much does it cost to fix common Mercedes-Benz C-Class problems?

What year Mercedes-Benz C-Class is the most reliable?

What is the 2001-2007 Mercedes-Benz C-Class SAM Module Failure?

What is the 2005-2013 Mercedes-Benz C-Class 7G-Tronic Valve Body Failure?

What is the 2008-2014 Mercedes-Benz C-Class W204 Rear Subframe Cracking?

What is the 2022-2025 Mercedes-Benz C-Class Front Seat Occupant Classification / Passenger Airbag Warning Faults?

What is the 2022-2025 Mercedes-Benz C-Class 48V Mild-Hybrid / Integrated Starter-Generator Failure Causing No-Start and Power Loss?

What is the 2022-2025 Mercedes-Benz C-Class MBUX / Instrument Cluster Black Screen, Rebooting, or No Rear Camera Image?

What is the 2008-2020 Mercedes-Benz C-Class Sunroof Drain Clog Water Damage?

What is the 2015-2021 Mercedes-Benz C-Class M274 Turbo Wastegate Rattle?

What is the 2012-2018 Mercedes-Benz C-Class Cam Adjuster Solenoid Failure?

What is the 2022-2025 Mercedes-Benz C-Class Driver Assistance Sensor Misalignment Causing 'Inoperative' Warnings and Disabled Features?

What is the 2022-2025 Mercedes-Benz C-Class Premature Front Brake Squeal, Judder, and Rotor/Pads Replacement?

What is the 2008-2018 Mercedes-Benz C-Class Door Lock Actuator Failure?