Powertrain, generic (extended)

P2CF2 Auxiliary Thermostat B Stuck Closed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P2CF2 is logged when auxiliary thermostat B does not open: the temperature in its loop keeps rising beyond the opening point while the controller expects it to level off. The loop assigned to B differs by maker, so the actual consequence can be an overheating cylinder head, hot engine oil or, if B guards a smaller branch, merely a local hot spot that the main gauge does not show. No manufacturer documents P2CF2 publicly; for thermostat A on the four-cylinder Lotus Emira the published check is whether the piston extends in hot water, and the same test applies here. Wax thermostats fail closed mainly through a leaking wax charge or a jammed piston. CARB covers systems with several thermostats under its cooling monitor. Treat it as an overheating risk.

Likely causes

Leaking wax charge, thermostat stays shut
Piston seized by corrosion or deposits
Temperature sensor of that loop reading too high

Symptoms

  • Engine warning lamp
  • Overheating warning or high oil temperature
  • Reduced power to protect the engine

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€120–800
Time1–4 h

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

Parts involved

aux thermostat bengine coolant loop

Related codes

P2CF1P2CF0P0217P026F

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