P2B66: Coolant Pump D Control Circuit/Open

P2B66 is the open-circuit code for the control line of coolant pump D, the pump a manufacturer labels D in its thermal management. The driver stage in the engine computer detects a broken wire, an unplugged connector or a pump input that no longer draws current. No manufacturer documents this exact code publicly. Ford's 2024 summary shows the analogous logic for pumps A and B (P2600, P261A): a continuous check from 11 V battery voltage, in which the smart driver reports the output fault. Under CARB 13 CCR 1968.2 (e)(15), output components must be watched for circuit faults. A short to ground is P2B67, a short to voltage P2B68; pumps C and E use P26F4 and P2DF4. Without control the pump stays off and its loop loses cooling.

Symptoms

• Warning lamp with stored code
• Pump D does not respond to commands
• Higher temperature in the loop served by pump D

Most likely causes

• Pump connector loose, corroded or unplugged
• Control wire broken between engine computer and pump
• Control input inside the pump open

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 continuity of the wire between the component and the control module.
3. Check the actual temperature in live data
4. Make sure the fan comes on when it should
5. Check the thermostat and connector
6. 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 P2B66 means

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

Frequently asked questions

Can I keep driving with code P2B66?

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 P2B66?

The most common causes are: pump connector loose, corroded or unplugged; control wire broken between engine computer and pump; control input inside the pump open.

Related codes

• P2B67Coolant Pump D Control Circuit Low
• P2B68Coolant Pump D Control Circuit High
• P2B69Coolant Pump D Supply Voltage Circuit
• P26F4Coolant Pump C Control Circuit/Open
• P2DF4Coolant Pump E Control Circuit/Open

Sources

• law.cornell.edu: 13 CCR 1968.2
• fordservicecontent.com: OBDSM2400OUTPUT 16Jul2024 WSM final V2 MCS7001

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.