Table of Contents
Service B on Mercedes C300: What It Covers & Why It Matters
On your Mercedes C300, the “Service B” reminder is triggered by the Flexible Service System (FSS), usually around 20,000 miles or 12 months after Service A. Service B is more comprehensive than Service A, ensuring your vehicle stays reliable, safe, and efficient.
It’s not just about oil changes Service B includes brake fluid, cabin filters, and deeper inspections designed to catch problems early. Keeping up with Service B is critical for maintaining performance, preserving warranty coverage, and protecting your investment.
For a full overview of all routine maintenance tasks and schedules, see our Mercedes Maintenance and Service Guide.
What Is Service B on Mercedes C300?
Service B is the second major scheduled service in Mercedes-Benz’s Flexible Service System. For the C300 (with the M274 engine), Service B is due at 20,000 miles or 2 years, whichever comes first.
Unlike Service A, which is more basic, Service B involves additional replacements and a more detailed inspection.
What’s Included in Service B?
Service B on Mercedes C300 typically includes:
| Service B Task | Details |
|---|---|
| Oil + Oil Filter Replacement | Genuine MB synthetic oil and OEM filter (MB 229.x spec) |
| Brake Fluid Exchange | Hydraulic system flush to prevent corrosion |
| Cabin Filter Replacement | Removes dust and pollen, improves HVAC airflow |
| Fluid Level Checks & Corrections | Includes coolant, transmission, brake, and steering fluids |
| Tire Inflation & Brake Inspection | Ensures proper tread and safe braking performance |
| Reset Maintenance Counter | Required to reset Service B reminder in the instrument cluster |
| Optional Add-ons | May include engine air filter, wiper blades based on model/region |
Service Timeline: A vs B
- – Service A: Every 10,000 mi / 1 year → Oil + filter, fluid checks, tire/brake inspection.
- – Service B: Every 20,000 mi / 2 years → All Service A tasks plus brake fluid, cabin filter, and deeper checks.
Sub-Services: B1 to B7 Explained
B2 Service Mercedes C300
- – Includes all B1 service items
- – Dust Filter Replacement: Replace dust filter.
- – Battery Check: Inspect battery condition and terminals.
B3 Service for Mercedes C300
- – Includes all B1 service items
- – Transmission Service: Check and replace transmission fluid if necessary, check the following link, How to check automatic transmission oil
- – Differential Oil Replacement: Replace the oil in the differential.
- – Additional Checks: May include additional specific checks depending on the model.
B4 Service Mercedes C300
- – Includes all B1 service items
- – Brake Fluid Flush: Replace brake fluid. keep reading, the steps below
- – Fuel Filter Replacement: Replace fuel filter.
- – Spark Plug Replacement: Replace spark plugs if required.
B5 Service Mercedes C300
- – Includes all B1 service items
- – Coolant Replacement: Replace engine coolant.
- – Belt and Hose Inspection: Inspect and replace belts and hoses if necessary.
- – Exhaust System Inspection: Check the exhaust system for leaks and damage.
B6 Service Mercedes C300
- – Includes all B1 service items
- – Drive Shaft Inspection: Inspect drive shaft for wear and tear.
- – Suspension Check: Inspect suspension components.
- – Air Filter Replacement: Replace engine air filter.
B7 Service Mercedes C300
- – Includes all B1 service items
- – Major Service Items: This may include extensive checks and replacements based on vehicle age/mileage.
- – Timing Belt Replacement: If applicable, inspect and possibly replace the timing belt.
- – Advanced Diagnostics: Comprehensive diagnostic check of all vehicle systems.
DIY vs Dealer/Independent Garage
| Task | DIY Possible? | Recommended For |
|---|---|---|
| Oil & filter change | Yes | DIY or quality indie shop |
| Cabin/engine air filter replacement | Yes | DIY |
| Brake fluid flush | Moderate – needs correct tool & bleeding procedure | Dealer or German specialist |
| Fluid level checks | Yes | DIY or indie |
| Reset maintenance reminder | Yes – via manual or OBD tool | DIY |
Engine air filter change Mercedes C300 Procedure
To change the engine air filter on Mercedes C300 equipped with a M274 gasoline engine, follow the following steps;
Step 1 : Remove
1. Remove the engine cover (6)
2. Unlock and disconnect the electrical connector (2)
3. Detach the clamp (3) and remove the air intake tube from the air filter housing cover (4)
4. Unscrew the screws (1). The screws (1) remain inside the air filter housing cover (4).
5. Remove the air filter housing cover (4)
6. Remove the air filter cartridge (5)
Step 2 : Clean
7. Clean the inside surface of the air filter housing and the air filter housing cover (4)
Step 3 : Install
8. Insert a new air filter cartridge (5) into the air filter housing
9. Place the air filter housing cover (4) and connect the air intake tube to the air filter housing cover (4)
Ensure the correct placement of the air filter housing cover (4) on the air filter housing to avoid damage.
10. Tighten the screws (1) fully
11. Position and tighten the clamp (3)
12. Connect and lock the electrical connector (2)
13. Install the engine cover (6)
How to brake fluid change ? Mercedes C300
Brake Fluid Change Instructions
- 1. Detach the cover (5) located above the brake fluid reservoir (6).
- 2. Clean around the cap of the brake fluid reservoir (6).
- 3. Remove the cap from the brake fluid reservoir (6).
- 4. Pour new brake fluid up to the “Max” mark in the brake fluid reservoir (6) using “Brake Fluid (DOT 4 plus)”.
- 5. Take off the front wheels.
- 6. Attach the filling device to the brake fluid reservoir (6).
- 7. Turn on the filling device “see image below”.
- 8. Raise the vehicle.
- 9. Proceed with the brake fluid purge.
- 10. Put the front wheels back on.
- 11. Lower the vehicle.
- 12. Turn off the filling device and disconnect it from the brake fluid reservoir (6).
- 13. Inspect the brake system for leaks.
- 14. Correct the fluid level in the brake fluid reservoir (6).
- 15. Close the brake fluid reservoir (6) with the cap.
- 16. Place the cover back above the brake fluid reservoir (6).
How to replace engine coolant ? Mercedes C300
To replace engine coolant you should follow the next steps;
Step 1 : Drain
- 1. Remove the expansion tank cap
- 2. Remove the central and front parts of the lower engine compartment cover.
- 3. Slide the drain hose (2) onto the drain fitting at the radiator.
- 4. Open drain screw (1), drain the coolant, and collect it in a suitable container.
Step 2 : Refilling
- 1. Tighten drain screw (1) completely and remove drain hose (2).
- 2. Refill with coolant and bleed the engine cooling system.
- 3. Check the tightness of the engine cooling system.
Why Service B Matters
- – Brake fluid absorbs moisture → reduced braking performance.
- – Cabin filters clog → poor air quality, HVAC strain.
- – Oil & fluid checks catch small issues before they escalate.
- – Resetting reminders keeps your service log and warranty valid.
How Often Should You Do Service B?
Mercedes-Benz recommends every 20,000 miles or 2 years (after Service A). Severe driving conditions (extreme climate, city traffic, towing) may require more frequent attention.
Cost of Service B on Mercedes C300
- – Average cost: $400–$600 (parts + labor).
- – Dealerships vs Independent Shops: Dealers may be higher but include official software resets and OEM parts. Independent German specialists may be more cost-effective.
Tips for Maintaining Your Mercedes C300
- 1. Stick to the A/B service schedule.
- 2. Check fluid levels monthly (oil, coolant, brake).
- 3. Monitor tire pressure regularly.
- 4. Address dashboard warning lights immediately.
- 5. Drive smoothly to reduce wear and fuel consumption.
FAQs
Q: Is Service B mandatory for Mercedes C300?
Yes, it’s part of the official schedule and required to maintain warranty coverage.
Q: How long does Service B take?
On average 2–3 hours, depending on add-ons (air filter, spark plugs, etc.).
Q: Can I skip Service B if I already did Service A?
No. Service B includes additional replacements and checks not covered in Service A.
Q: What happens if I delay Service B?
You risk brake fluid corrosion, clogged filters, reduced performance, and voided warranty coverage.
Conclusion
Service B on Mercedes C300 is an essential milestone in the maintenance cycle. By following the official schedule and addressing key items like brake fluid, cabin filters, and inspections, you ensure your car continues to deliver the performance and luxury Mercedes is known for. Regular Service B not only enhances safety and reliability but also helps you avoid expensive repairs later.
Author
Written by Mercedes Expert
With years of hands-on experience diagnosing and repairing Mercedes-Benz systems, he brings technical depth and practical case studies to help car owners, technicians, and enthusiasts troubleshoot complex automotive issues. His work focuses on clear repair guides, OEM-level procedures, and knowledge-sharing to empower both professionals and drivers.
Last Updated: September 2025
