P251F: PTO Engine Shutdown Circuit High

P251F is the high-side fault of the PTO engine shutdown input: the voltage stays near supply level where the module expects a defined switching state. A shutdown wire touching a powered circuit in the body harness, a missing ground on the equipment controller, or an add-on module that drives the line permanently are typical. The main risk is that a real stop request from the body equipment is no longer recognised, or that the module locks out PTO operation as a precaution. Public maker documentation for P251F was not found; CARB covers PTO units in its OBD rules, and GM's PIP6108 on P251A illustrates how ground faults distort PTO-related inputs on medium-duty trucks. P251D is the open-circuit and P251E the low-level variant.

Symptoms

• Engine does not stop when equipment shutdown is triggered
• PTO operation blocked

Most likely causes

• Shutdown wire shorted to a powered circuit in the body harness
• Body equipment controller without ground
• Retrofitted control module holding the line high

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery, connectors, and wiring
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Read the live data with a scanner
4. Follow the manufacturer's service manual

Good to know

• Repair difficulty: medium

What each character of P251F means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 5: Speed and idle
• 1F: Specific fault in that system

Frequently asked questions

Can I keep driving with code P251F?

If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.

What causes code P251F?

The most common causes are: shutdown wire shorted to a powered circuit in the body harness; body equipment controller without ground; retrofitted control module holding the line high.

Related codes

• P251DPTO Engine Shutdown Circuit/Open
• P251EPTO Engine Shutdown Circuit Low
• P251CPTO Enable Switch Circuit High

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 11031511 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.