Powertrain, generic (extended)

P26AC Engine Coolant Bypass Valve B Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Which valve carries the letter B depends on the maker. Ford names it in its gasoline OBD summaries for 2020–2023 and 2024–2025: valve B is the active transmission cooling valve, which sends engine coolant to the automatic transmission oil cooler, while valve A heats the transmission. P26AC is set when the smart driver in the PCM reports a fault on that output for 5 s; in 2024 Ford also files it under the extended code P26AC_13 for an open circuit. CARB lets makers combine open, low and high faults of an output into one code, which is why P26AC is often the only electrical code used. With the valve unpowered, transmission oil may run hotter or colder than intended.

Likely causes

Broken wire or unplugged connector at valve B
Open solenoid or motor winding in the valve
Faulty output driver in the PCM

Symptoms

  • Check engine light
  • Transmission fluid temperature higher than normal when towing
  • Usually no change in normal driving

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–600
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

P26ADP26AEP26AFP26B0P2681P26B7

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