P2B65: Coolant Pump B Overspeed/Air in System

When a coolant pump draws in air, its impeller loses load: speed climbs and current drops. P2B65 reports this for coolant pump B. Ford's 2024 gasoline OBD summary lists it as failure type B1 (overspeed/dry run) of pump B under P261A. Bentley stores P2B6500, labelled air in system and static, in both engine control units 0001 and 0011 of the W12 Continental GT, GTC and Flying Spur from model years 2018 to 2024, often together with P2B8600 for pump A and a coolant warning in the instrument panel. Bentley's bulletin 2066669 (revisions 1 to 4, latest November 2025) starts with a pressure test and then checks vent hose 975 122 447H, whose built-in check valve can restrict flow; after replacement the circuit is bled. Pump D has P2B6C.

Symptoms

• Coolant or overheating warning in the instrument cluster
• Falling coolant level in the expansion tank
• Gurgling noise or fluctuating temperature display

Most likely causes

• Air left in the circuit after filling or repair
• Coolant loss through a leak, level too low
• Restricting check valve in the vent hose (Bentley W12, 975 122 447H)
• Speed or current detection inside the pump faulty

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, check the coolant level; never do this when the system is hot
2. Check the actual temperature in live data
3. Make sure the fan comes on when it should
4. Check the thermostat and connector
5. Measure the sensor and replace it if its readings do not make sense

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P2B65 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• B: Subsystem depends on the code range
• 65: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2B65?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P2B65?

The most common causes are: air left in the circuit after filling or repair; coolant loss through a leak, level too low; restricting check valve in the vent hose (Bentley W12, 975 122 447H).

Related codes

• P2B86Coolant Pump A Overspeed/Air in System
• P2B63Coolant Pump B Stuck/Stalled
• P2B64Coolant Pump B Control Module Overtemperature
• P2B6CCoolant Pump D Overspeed/Air in System
• P261BCoolant Pump B Control Circuit Performance/Stuck Off

Sources

• fordservicecontent.com: OBDSM2400OUTPUT 16Jul2024 WSM final V2 MCS7001
• static.nhtsa.gov: MC 10211208 0001
• static.nhtsa.gov: MC 10245070 0001
• static.nhtsa.gov: MC 11026443 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.