Powertrain, generic (extended)

P22C8 Turbocharger Compressor Outlet Valve Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P22C8 is a functional fault: the compressor outlet valve stays open at a moment when the control strategy expects it shut, so pressure or airflow in the boost path does not follow the command. Mercedes-Benz uses it on the M256.8 inline six with its 48-volt electric auxiliary compressor. Bulletin LI09.41-P-078735 in its second version (March 2025) added P22C800 next to P22C900 for E, CLS, GLE and GLS 450, S 500/580 e and AMG 53 models and blames a jammed check valve in the charge-air pipe; the fix is a new charge-air line with integrated check valve. Listed symptoms are the warning lamp, weak output and faulty boost. Because the module must see the valve misbehave under suitable load, the code usually needs a test drive to confirm. P22C9 is the opposite case, a valve stuck shut.

Likely causes

Check valve in the charge-air pipe jammed (Mercedes M256)
Oil film or deposits holding the valve flap open
Actuator or linkage no longer able to close the valve

Symptoms

  • Check engine light on
  • Little or poor power output
  • Boost builds poorly or unevenly

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 valve

Related codes

P22C9P22C5P22CDP0299

References: static.nhtsa.gov, law.cornell.edu, patents.google.com.