P26C1: Engine Coolant Bypass Valve D Range/Performance

P26C1 means valve D works electrically but does not deliver the expected effect. Ford is the documented user, and on its plug-in hybrids valve D governs the cabin heating loop. Ford special service message 50325 and bulletin 22-2127 cover 2020–2022 Escape and 2021–2022 Corsair PHEVs that set P2183 for the second coolant temperature sensor, at times with an overheat warning; P26C1 can follow as a consequence. The root cause was a PCM soak timer that miscalculated how long the electric cabin heater had been off, so the fix is reprogramming several modules, starting with the PCM; checking coolant level and the ECT 2 connector came first. Ford's public summaries give no thresholds for P26C1. Diagnose P2183 before replacing the valve.

Symptoms

• Check engine light
• Engine overheat message in the cluster
• P2183 stored at the same time

Most likely causes

• PCM software miscalculating heater soak time (Ford PHEV)
• Contaminated connector of coolant temperature sensor 2
• Valve D moving slowly or sticking
• Low coolant level

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. Compare the reading with other engine data while varying the engine speed.
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 P26C1 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 6: Control modules and outputs
• C1: Specific fault in that system

Frequently asked questions

Can I keep driving with code P26C1?

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 P26C1?

The most common causes are: pCM software miscalculating heater soak time (Ford PHEV); contaminated connector of coolant temperature sensor 2; valve D moving slowly or sticking.

Related codes

• P2183Engine Coolant Temperature Sensor 2 Circuit Range/Performance
• P26C0Engine Coolant Bypass Valve D Stuck/Open
• P26C2Engine Coolant Bypass Valve D Stuck Closed
• P26BDEngine Coolant Bypass Valve D Control Circuit/Open

Sources

• static.nhtsa.gov: MC 10210387 0001
• static.nhtsa.gov: MC 10205448 0001
• fordservicecontent.com: OBD Operations Summary Gasoline 2020 2023

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.