Powertrain, generic (extended)

P22C9 Turbocharger Compressor Outlet Valve Stuck Closed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P22C9 says the compressor outlet valve did not open when commanded, so air from the compressor it controls cannot reach the engine and the expected boost is missing. Mercedes-Benz documents the code for the M256.8 six-cylinder: the first version of bulletin LI09.41-P-078735 (December 2024) covers P22C900 in the MRG3 engine control unit on models from 2019 to 2025 and traces it to a check valve in the charge-air pipe that is jammed shut; the charge-air line with integrated check valve is replaced. Symptoms listed there are the engine lamp, reduced output and a boost malfunction. The check runs only under operating conditions that call for the valve to open, so confirmation usually takes a drive under load. Unlike P22C8, the risk here is a blocked path in which a compressor works against a closed outlet.

Likely causes

Check valve in the charge-air pipe jammed shut (Mercedes M256)
Valve actuator, vacuum or pressure supply unable to open the valve
Valve seized by deposits or corrosion

Symptoms

  • Check engine light on
  • Noticeable loss of power under load
  • Boost malfunction, possibly with underboost code

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–800
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

diverter valveturbocharger

Related codes

P22C8P22C5P22CEP0299

References: static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.