Powertrain, generic (extended)

P2CF0 Auxiliary Thermostat A Stuck Closed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P2CF0 is the closed-side counterpart of P2CEF: auxiliary thermostat A fails to open, so the circuit it governs gets too little flow and its temperature climbs past the regulating point while other parts of the engine may look normal. No manufacturer documents P2CF0 publicly. The same component is described by Lotus for the four-cylinder Emira, where A is the medium-temperature thermostat and the workshop test checks that the cold piston is retracted and extends in hot water; a unit that never extends would match this code. Wax thermostats usually stick shut when the wax charge leaks or dirt jams the piston. CARB has required monitoring plans since 2019–2021 for systems with several thermostats and temperature sensors. Overheating in that loop is the risk, so it needs prompt attention.

Likely causes

Wax element lost its charge, thermostat no longer opens
Piston jammed by deposits or debris
Air pocket around the element after a coolant service, so it never sees hot coolant

Symptoms

  • Engine warning lamp
  • High temperature in one cooling circuit or an overheating warning
  • Possible power reduction to protect the engine

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–900
Time1–4.5 h

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

Parts involved

aux thermostat aengine coolant loop

Related codes

P2CEFP2CF2P0217P026F

References: law.cornell.edu, static.nhtsa.gov, en.wikipedia.org.