P26FB
EGR Cooler Bypass Control Stuck Closed Bank 1
The EGR cooler bypass valve on bank 1 is stuck in the closed position. EGR gas always passes through the cooler, which slows engine warm-up and can degrade cold-start emissions.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- Valve flap seized closed by sootCommon
- Actuator linkage jammed in closed positionPossible
- Carbon or debris buildup preventing free movementLess likely
Parts involved
- EGR Cooler Bypass Valve B1
- Bypass Actuator
P26FB 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.