Powertrain, generic (extended)

P26BF Engine Coolant Bypass Valve D Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P26BF stands for battery voltage on the valve D control line where the driver expects a switched or grounded level. Ford documents it in its 2024–2025 gasoline OBD summary: the cabin heating bypass valve is valve D, and a short to battery reported by the PCM's smart driver is stored as P26BF, internally also as P26BD_12, after continuous monitoring for 5 s. The 2020–2023 summary still listed only P26BD for this valve, so older Fords report the same fault under the general code. GM's public tables do not use P26BF. A short to positive can keep a low-side switched valve permanently on or trip the driver protection. Since this valve controls heater flow, expect heat that cannot be turned down or does not come at all.

Likely causes

Control wire shorted to battery voltage
Harness damaged near hot or moving engine parts
Internal fault in valve D

Symptoms

  • Check engine light
  • Heater stays hot or stays cold regardless of setting

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–500
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant bypass valve dsolenoidwiring harness

Related codes

P26BDP26BEP26B9

References: fordservicecontent.com, fordservicecontent.com, law.cornell.edu.