What Does P0121 Mean on a 2022 Mercedes-Benz C-Class?
A P0121 code on your 2022 Mercedes-Benz C-Class (W206—first year of this generation) means the ECU has caught the throttle position sensor (TPS) sending a signal that doesn't match expected patterns. The voltage is within range but the behavior is inconsistent with your driving inputs. Mercedes' engine management has identified a throttle system clue worth investigating.
The 2022 C-Class features the M254 2.0L turbocharged four-cylinder with 48V EQ Boost mild-hybrid technology. It uses direct fuel injection and the electronic throttle body integrates the TPS. As a first-year model on the W206 platform, software calibration issues are a significant possibility alongside carbon buildup from the DI engine.
Top Causes of P0121 on the 2022 C-Class
- Carbon buildup on throttle body – DI engines accumulate deposits; 2-4 years is enough. Likelihood: 35%
- ECU software calibration – First-year W206 platform; Mercedes released updates. Likelihood: 30%
- Throttle body assembly issue – Internal TPS defect. Likelihood: 15%
- Connector or wiring issue – Corrosion or loose fit. Likelihood: 12%
- 48V system interaction – ISG affecting throttle correlation. Likelihood: 8%
Symptoms You May Notice
- Check Engine Light on MBUX display
- Rough or inconsistent idle
- Hesitation during acceleration
- EQ Boost transitions feel rough
- Reduced power message
- Cruise control issues
How Serious Is This Code?
P0121 is medium severity. Your 2022 C-Class remains drivable with potentially reduced performance. Address it soon—within 1-2 weeks.
Diagnostic Steps
- Scan for codes using an OBD-II scanner—Mercedes XENTRY preferred
- Check ECU software version and available updates
- Inspect throttle body for carbon deposits
- Monitor TPS voltage: ~0.5V idle, smooth sweep to ~4.5V WOT
- Check throttle body connector integrity
- Verify 48V system operation and interaction with throttle
Estimated Repair Costs
- Under warranty: $0 (4-year/50,000-mile warranty may still apply)
- Throttle body cleaning: $150–$300 (DIY: $15–$25)
- Throttle body replacement: $550–$1,000
- ECU software update: $150–$250 at dealer (if out of warranty)
Can You DIY This Fix?
DIY feasibility is low to moderate. Check your warranty first—the 2022 C-Class should still be under Mercedes' 4-year/50,000-mile warranty. If covered, let the dealer fix it for free. If out of warranty, throttle body cleaning is possible but Mercedes' engine bay is tightly packaged. You'll need a Mercedes-compatible scanner for proper diagnosis and code clearing.