P251B
PTO Enable Switch Circuit Low
The PTO enable switch input reads stuck low — typically a short to ground or a permanently closed switch. The ECM either sees PTO enabled when the operator has not requested it, or cannot release the PTO mode after work.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Switch wire shorted to groundCommon
- Switch stuck closedPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Pto Enable Switch
- Wiring Harness
P251B 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.