Powertrain, generic (extended)

P26B8 Engine Coolant Bypass Valve C Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

With P26B8 a drive line of valve C is pulled toward ground. The best public description comes from GM's 2025 ECM table 25OBDG04B for the six-cylinder diesel: valve C sits on an H-bridge, and the controller looks for a grounded line separately in the opening and the closing direction, each time only while the other direction is free of the same fault. The result is a Type B code, so the lamp normally lights on the second trip. GM bulletin 21-NA-149 lists P26B8 among many codes that a chafed engine harness can trigger on 2019–2021 trucks and SUVs with gasoline V6/V8, 2.7L turbo or 3.0L diesel engines. Ford has no separate low code here. A grounded line can stall the valve or blow the driver, leaving engine temperature less well controlled.

Likely causes

Drive wire chafed against the engine or body and shorted to ground
Internal short in the valve C motor
Water or coolant in the valve connector

Symptoms

  • Check engine light after two trips
  • Unstable or high coolant temperature
  • Further valve or harness codes stored at the same time

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

P26B7P26B9P26BBP26BE

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.