What are the common causes of P2CF2?

An auxiliary thermostat B stuck closed. A coolant flow path blocked at the auxiliary thermostat B. A binding auxiliary thermostat B valve. Air in the coolant system at the auxiliary thermostat.

Read auxiliary thermostat B commanded and actual position. Compare coolant temperatures across the auxiliary thermostat B. Check for a coolant flow blockage. Test the auxiliary thermostat B for free travel. Replace auxiliary thermostat B if it stays closed. Clear the code and retest.

P2CF2

Auxiliary Thermostat B Stuck Closed

System: Powertrain control (P code)
Lamp: Check Engine Light
Category: Powertrain - Hybrid Propulsion

What it means

P2CF2 means Auxiliary Thermostat B Stuck Closed.

Check these first

An auxiliary thermostat B stuck closed
A coolant flow path blocked at the auxiliary thermostat B
A binding auxiliary thermostat B valve
Air in the coolant system at the auxiliary thermostat

What to do next

Read auxiliary thermostat B commanded and actual position
Compare coolant temperatures across the auxiliary thermostat B
Check for a coolant flow blockage
Test the auxiliary thermostat B for free travel
Replace auxiliary thermostat B if it stays closed
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.