P25BB
Regeneration Control Switch Circuit Low
Regeneration control switch input reads stuck low — short to ground or stuck-closed contact. The ECM may see a constant regen request which it cannot service while the vehicle is moving.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Switch wire shorted to groundCommon
- Connector pins corroded - high contact resistanceLess likely
- Harness chafing through insulationLess likely
Parts involved
- Regen Request Switch
P25BB 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.