P26B1
Engine Coolant Bypass Valve A Stuck Closed
The coolant bypass valve A is stuck closed. Coolant cannot bypass the radiator during warm-up so warm-up takes longer and emissions in the warm-up phase rise.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Valve seized closed by debrisCommon
- Actuator linkage jammed in closed positionPossible
- Carbon or debris buildup preventing free movementLess likely
Parts involved
- Coolant Bypass Valve A
- Thermostat Housing
P26B1 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.