P26BD: Engine Coolant Bypass Valve D Control Circuit/Open

P26BD is the open-load or general circuit fault on the output that drives coolant bypass valve D. Ford is the documented user. Both editions of its gasoline OBD summary, 2020–2023 and 2024–2025, assign valve D to cabin heating, meaning the valve that routes engine coolant to the heater core, and set P26BD once the PCM's smart driver signals an output fault during continuous 5 s monitoring; the 2024 edition adds the extended form P26BD_13. Ford's 2014 code list for spark-ignition engines already names P26BD with the Circuit/Open wording. GM's public tables do not use P26BD. Because the valve mainly serves the heater, the usual effect is too little or uncontrolled cabin heat rather than an engine problem. P26BE and P26BF cover shorted lines.

Symptoms

• Check engine light
• Weak or no cabin heat
• Heater output that cannot be regulated

Most likely causes

• Open coil or motor winding in valve D
• Loose or corroded valve connector
• Broken drive wire between PCM and valve

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 affects emissions.

What each character of P26BD means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 6: Control modules and outputs
• BD: Specific fault in that system

Frequently asked questions

Can I keep driving with code P26BD?

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 P26BD?

The most common causes are: open coil or motor winding in valve D; loose or corroded valve connector; broken drive wire between PCM and valve.

Related codes

• P26BEEngine Coolant Bypass Valve D Control Circuit Low
• P26BFEngine Coolant Bypass Valve D Control Circuit High
• P26C1Engine Coolant Bypass Valve D Range/Performance
• P26B7Engine Coolant Bypass Valve C Control Circuit/Open

Sources

• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023
• fordservicecontent.com: OBDSM2400OUTPUT 16Jul2024 WSM final V2 MCS7001
• performanceparts.ford.com: 2014 BOSS 302S OBDII Codes

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.