Powertrain, generic (extended)

P26AB Engine Coolant Bypass Valve A Stuck/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P26AB is stored when valve A stays open although it was told to close. Ford's hybrid summaries (2014–2019) define the valve as the switch between a combined loop, with engine coolant through the heater core, and an isolated loop heated by a PTC heater; if the second coolant sensor reads more than 5 °F above the engine sensor within 60 s of a circuit fault, the valve is judged stuck in the combined loop, and P2682 must set first. On 2016–2017 smart fortwo cars a corroding vacuum change-over valve keeps the heater shut-off valve open, so Mercedes-Benz extended its warranty to 10 years. Ram 1500 trucks of 2013–2015 (3.6, 4.7 and 5.7 L) and 3.0 L diesels received PCM flashes that list P26AB.

Likely causes

Valve jammed open by deposits, wear or a broken drive part
Corroded vacuum change-over valve (smart fortwo 453)
Engine control software misjudging valve state (Ram flashes)
Drive circuit fault leaving the valve in its open default

Symptoms

  • Check engine light
  • Engine takes long to warm up, higher fuel use when cold
  • Heater works with engine off only poorly (hybrids)

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–700
Time0.3–2.5 h

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

Parts involved

coolant bypass valve athermostat housing

Related codes

P26B1P26AFP2682P2681P26A3P26A9

References: fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.