What Does P0172 Mean on Your 2022 Mercedes-Benz C-Class?
A P0172 trouble code on your 2022 Mercedes-Benz C-Class (W206) tells you the engine management system has detected a rich air-fuel condition on Bank 1. The 2022 C 300 introduced the M254 2.0-liter turbocharged four-cylinder engine with 255 horsepower and a 48-volt mild-hybrid system. This single-bank engine triggers P0172 when the air-fuel mixture consistently runs richer than the target stoichiometric ratio.
With the 2022 model having a few years of service, it is important to address P0172 before it causes expensive downstream damage to emission components.
Symptoms You Might Notice
- Check engine light or engine warning on MBUX display
- Decreased fuel economy
- Black or sooty exhaust smoke
- Strong gasoline smell from the exhaust
- Rough idle or engine vibration
- Reduced acceleration or boost
Common Causes of P0172 on the 2022 C-Class
- Dirty or Failing MAF Sensor - The M254 engine's hot-film air mass sensor can accumulate oil residue and debris after a few years, leading to under-reading of airflow and over-fueling.
- Crankcase Ventilation Issue - The crankcase vent valve can allow excess oil vapors into the intake manifold, enriching the air-fuel mixture. This is a common issue on German turbo engines.
- Leaking Direct Fuel Injector - High-pressure piezo injectors can develop carbon deposits or seal leaks with use, causing them to deliver more fuel than commanded.
- Upstream Lambda Sensor Drift - The wideband lambda sensor can drift from calibration over time, sending inaccurate data to the ECU and causing incorrect fuel trim adjustments.
How to Diagnose the Problem
Use a Mercedes-compatible scan tool to read fault codes and engine adaptations. Review fuel trim corrections for Bank 1. Negative multiplicative corrections confirm the ECU is reducing fuel to compensate for rich running. Look for companion codes that might point to a specific component.
Start with an air filter check and MAF sensor cleaning. Inspect the intake for oil contamination (CCV indicator). Test the lambda sensor with the diagnostic tool's live data. If corrections remain abnormal, perform injector diagnostics.
Repair Options and Cost Breakdown
- Air filter replacement - $30 to $60.
- MAF sensor cleaning or replacement - $15 to $430.
- Crankcase ventilation valve replacement - $240 to $490.
- Lambda/O2 sensor replacement - $270 to $480.
- Direct fuel injector replacement - $420 to $920.
Prevention Tips
Premium fuel is required for the M254 engine. Use Mercedes-approved synthetic oil and change it on schedule. Keep the air filter fresh. Have the fuel system inspected during regular service intervals. If you notice any change in fuel economy or engine behavior, have it checked before it escalates to a check engine light.