Powertrain, generic (extended)

P2CD5 Turbocharger/Supercharger Bypass Valve C Stuck

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Bypass valve C is a third compressor recirculation valve, which only exists on layouts with three charging paths or stages; on lift-off it routes boosted air back to the compressor inlet so the compressor does not surge. It is not the wastegate. P2CD5 says the valve no longer moves when commanded and stays in one position. No manufacturer documents P2CD5 publicly. GM shows the two usual methods on its A and B valves: the 2019 Corvette LT5 flags P23AA when the position error exceeds 25 % for 1 s while the valve speed stays within ±10 %/s (Type A), and the 2019 CT6 twin-turbo infers a stuck dump valve on bank 2 from airflow and pressure behaviour (P00C4). A circuit fault on valve C is P25F8, a general mechanical fault P25FC. Stuck shut means surge noise on lift-off, stuck open means missing boost.

Likely causes

Valve or piston seized by oil and soot deposits from the crankcase breather
Electric actuator or diaphragm of the valve worn or failed
Missing vacuum or control signal on a pneumatically operated valve
Position feedback reports movement wrongly although the valve works

Symptoms

  • Fluttering or surging noise from the intake when lifting off the throttle
  • Boost builds slowly or stays low when the valve is stuck open
  • Warning lamp on and engine power limited

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–1,200
Time1–4 h

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

Parts involved

turbo bypass valve c

Related codes

P2C29P25F8P25FCP23AAP00C4P0033

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, en.wikipedia.org.