Powertrain, generic (extended)

P26BA Engine Coolant Bypass Valve C Stuck/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P26BA is meant for a valve C that stays open although the controller wants it shut, while its circuit tests fine. No manufacturer documents this code in public sources. GM and Ford, which both use the letter C, cover their valve C functionally through other codes: GM's L3B and diesel tables treat a valve that misses its target angle as P26BB, and Ford watches its radiator bypass only electrically. How an open-stuck check can be built is shown by GM's block valve logic for P26C0, which needs a position error of at least 10° while the feedback still reports the open side. CARB requires a functional test of output components where feasible. If the valve hangs open, coolant flows when it should not, so warm-up is slow and the engine may stay below its target temperature.

Likely causes

Valve C jammed in the open position by wear or deposits
Dirty or mixed coolant hindering valve movement
Incorrectly learned end positions after a repair

Symptoms

  • Check engine light
  • Slow warm-up and lower temperature gauge reading
  • Weak cabin heating in cold weather

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–800
Time1–3.5 h

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

Parts involved

coolant bypass valve cthermostat housing

Related codes

P26BBP26BCP26B7P0128

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