Air trapped in the coolant system, causing the pump to run dry and overspeed; Low coolant level due to a leak or improper filling procedure; Faulty coolant pump B, such as internal wear or a failing bearing; Blocked or restricted coolant passage in the battery pack or hoses; Damaged wiring or connector at the coolant pump, causing erratic speed signals; Failed coolant pump control module or relay; Incorrect coolant mixture causing cavitation and air bubbles

DTC codes / P2Cxx · Hybrid propulsion / P2CF6

P2CF6Hybrid/EV Battery Pack Coolant Pump B Overspeed /Air in System

P2CF6 indicates that the hybrid or electric vehicle battery pack coolant pump B has been commanded to run at a speed that the control module considers excessive, or that air has been detected in the coolant system, causing the pump to overspeed. The computer monitors pump speed and coolant flow, and when the actual speed exceeds the expected value for the given conditions, it sets this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the hybrid system warning light or service vehicle soon message
Reduced electric driving range or performance due to battery thermal management entering a limp mode
Audible whining or grinding noise from the coolant pump area
Overheating of the high-voltage battery pack, which may trigger additional codes or power reduction
Often no symptoms besides the warning light, especially if the overspeed is intermittent

Common causes, most likely first

Air trapped in the coolant system, causing the pump to run dry and overspeed
Low coolant level due to a leak or improper filling procedure
Faulty coolant pump B, such as internal wear or a failing bearing
Blocked or restricted coolant passage in the battery pack or hoses
Damaged wiring or connector at the coolant pump, causing erratic speed signals
Failed coolant pump control module or relay
Incorrect coolant mixture causing cavitation and air bubbles

How to diagnose and fix it

Check coolant level and inspect for leaks; top up with the specified coolant if low
Perform a coolant bleed procedure using a vacuum fill tool to remove trapped air
Scan live data for coolant pump speed and compare commanded versus actual speed
Inspect the coolant pump wiring and connectors for corrosion or damage
Test the coolant pump for mechanical binding or abnormal noise; replace if faulty
Check for restricted coolant hoses or a clogged battery pack coolant channel
Verify the coolant pump control module operation and replace if necessary

Air in the system mimics a failed pump

A common mistake is replacing the coolant pump when the real problem is air trapped in the system after a coolant service or repair.
The code can set intermittently due to a loose pump connector that only loses contact during vibration or temperature changes.
Some vehicles require a specific bleed procedure using a scan tool to activate the pump and purge air; skipping this step leads to repeat codes.
A restricted coolant passage in the battery pack can cause the pump to overspeed as it tries to maintain flow, mimicking a pump fault.
Always check for related codes such as P2CF5 or P0A93 that may indicate a pump performance issue rather than overspeed.

Can I keep driving with P2CF6?

It is not advisable to continue driving with this code because battery overheating can lead to reduced power and potential damage to the high-voltage battery. If the warning light is on, limit driving to a short distance to a repair facility and avoid aggressive acceleration or high-speed driving.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.