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Rough Shifts on My 2017 C300 - Time for Transmission Fluid Service?

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Chris P. · rep 0 · May 25, 3:08 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz C300

Hey everyone,

I've noticed my 2017 Mercedes-Benz C300 (W205, 9G-TRONIC transmission) has been shifting a bit rough lately, especially from 2nd to 3rd gear. It's got about 75,000 miles on it now, and I'm not sure if the transmission fluid has ever been changed. The dealership said it might be 'lifetime' fluid, but I've heard otherwise from independent shops.

Is it really necessary to change the transmission fluid on these cars? If so, what's the recommended interval, and is this something a competent DIYer can tackle, or is it strictly a dealer job due to special tools or procedures? I'm trying to avoid any major issues down the road.

Thanks for any insights!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:08 AM

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ClearTheCode admin answer:

It's a common misconception that modern Mercedes-Benz transmissions use 'lifetime' fluid. While the service interval is longer than older models, Mercedes-Benz does recommend transmission fluid and filter service, especially for the 9G-TRONIC (725.0) transmission. For your 2017 C300, the recommended service interval is typically around 60,000 miles or 6 years, whichever comes first. Given your mileage and symptoms, it's definitely time for this service.

Causes of Rough Shifting:

  1. Degraded Transmission Fluid: Over time, transmission fluid loses its lubricating properties and can accumulate metallic particles, leading to increased friction and rougher shifts.
  2. Clogged Transmission Filter: A dirty filter restricts fluid flow, impacting hydraulic pressure and shift quality.
  3. Software Adaptations: Sometimes, rough shifts can be addressed with a transmission control module (TCM) software update or adaptation reset, but this is usually done after fluid service.

DIY vs. Professional Service: While technically possible for a DIYer, a 9G-TRONIC transmission fluid change is more complex than older models and requires specific tools and procedures:

  1. Special Fluid: Requires specific Mercedes-Benz approved ATF (MB 236.17 specification).
  2. Temperature Monitoring: Accurate fluid level setting requires monitoring the transmission fluid temperature with a diagnostic tool (like XENTRY/DAS or a good aftermarket scanner).
  3. Fill Plug Location: The fill plug is often located on the bottom of the transmission, requiring a specialized pump to push fluid in.
  4. Drain and Fill Procedure: It's not a simple drain-and-fill; a specific sequence is followed to ensure proper fluid circulation and level.

When to See a Shop:

  • Lack of Specialized Tools: If you don't have a fluid pump, a diagnostic scanner for temperature, and the correct fluid, it's best left to a professional.
  • Persistent Rough Shifting: If the rough shifting continues after a proper fluid and filter change, it could indicate internal transmission wear or a TCM issue, requiring further diagnostic by a Mercedes specialist.
  • OBD Codes: While rough shifting might not always trigger a code, if you see a P0700 (Transmission Control System Malfunction) or other transmission-related codes, a professional diagnosis is essential.
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