Powertrain, generic (extended)

P26B9 Engine Coolant Bypass Valve C Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P26B9 reports supply voltage where the valve C driver should see none, in practice a short to battery positive. Two makers document it. Ford's 2024–2025 gasoline summary pairs it with the open-circuit code as P26B9/P26B7_12: the smart driver for the radiator bypass valve flags the fault and the PCM stores it after 5 s of continuous monitoring. The 2020–2023 edition did not yet list a high code. GM's 2025 diesel table 25OBDG04B watches both motor directions of the H-bridge for a line shorted to positive, Type B, and GM bulletin 21-NA-149 names P26B9 among the codes a chafed engine harness can cause. A shorted line may force the motor against an end stop or make the driver shut down, so cooling control is degraded until the wire is repaired.

Likely causes

Drive wire shorted to a battery-voltage circuit
Engine harness damaged by chafing or heat
Internal fault in the valve C actuator

Symptoms

  • Check engine light
  • Temperature gauge higher or more erratic than usual
  • Valve does not respond to scan tool commands

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–650
Time0.5–3 h

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

Parts involved

coolant bypass valve csolenoidwiring harness

Related codes

P26B7P26B8P26BBP26BF

References: fordservicecontent.com, gsi.ext.gm.com, static.nhtsa.gov.