P0456 on Your 2020 C-Class: Following the Evidence
Your 2020 C-Class (W205—final years of this generation) has triggered P0456—a very small EVAP leak. The M264 2.0L turbo (or M276 V6 on C43 AMG) uses Mercedes's leak detection pump and activated charcoal filter. Basic warranty (4yr/50k) expired. Federal emissions (8yr/80k) covers EVAP through 2028.
Clues
- Check engine light on
- P0456 stored
- No performance symptoms
- Fuel filler seal may show wear after 5+ years
Suspects
- Fuel Filler Seal (High Likelihood): Five years of wear. $15–$35.
- Leak Detection Pump (High Likelihood): Well-documented Mercedes failure. Under emissions warranty or $280–$500.
- Purge Valve (Medium Likelihood): Turbo heat cycling. Under emissions warranty or $180–$380.
- EVAP Hose (Medium Likelihood): Rubber deterioration. $160–$320.
- Activated Charcoal Filter (Low Likelihood): Carbon degradation over 5 years. $350–$600.
Diagnostic Steps
- Check/replace fuel filler seal—$15–$35
- Check federal emissions warranty—8yr/80k through 2028
- Mercedes dealer or independent specialist—STAR diagnostics
- Smoke test if out-of-pocket ($100–$180 at Mercedes shop)
Costs
- Fuel filler seal: $15–$35
- Leak detection pump: $280–$500 (may be emissions covered)
- Purge valve: $180–$380
- Federal emissions 8yr/80k through 2028
Can I Drive?
Yes. P0456 has zero impact on the turbo, 4MATIC, or performance.
Warranty
Basic 4yr/50k expired. Federal emissions 8yr/80k covers EVAP through 2028. Mercedes repairs are expensive—use emissions warranty if eligible. Independent Mercedes specialists can save significantly on out-of-pocket work.