Powertrain, generic (extended)

P26AD Engine Coolant Bypass Valve B Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P26AD indicates a drive line of valve B pulled to ground. GM uses the code differently from the title: on the second-generation Volt (2016 table, VICM) the single coolant bypass valve has an H-bridge motor with two drive lines, and P26AD stands for driver 2 reporting a short to low while the valve is commanded toward the high position. Four failures in five samples at 100 ms set it as Type B; it is one of the codes that blocks P26A5, P26A9 and P15C5. Ford's 2014 gasoline list and its 2020–2025 summaries do not use P26AD. CARB requires output circuit faults to be detected but does not demand separate codes for each fault type. Expect a chafed wire to ground or a shorted motor winding.

Likely causes

Drive wire chafed and shorted to ground
Shorted valve motor winding
Coolant or water in the connector creating a leak path

Symptoms

  • Check engine light after two drives (GM)
  • Valve no longer moves, heating or warm-up affected

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–700
Time0.5–2.5 h

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

Parts involved

coolant bypass valve bsolenoidwiring harness

Related codes

P26AEP26ACP2682P26A9

References: gsi.ext.gm.com, law.cornell.edu.