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P255CPTO Speed Selector Sensor/Switch 2 Circuit Low

The PTO speed selector sensor/switch 2 circuit is stuck below its minimum expected voltage, usually from a short to ground or failed switch.

Definition

The PCM expects the second PTO speed selector input to stay within a calibrated voltage window, and P255C sets when the signal is pegged low — typically under about 0.25V — which indicates a short to ground, a failed selector, or a missing reference supply. While the fault is active, PTO speed control tied to this input is disabled or defaulted, and a MIL may set; normal on-road operation is unaffected.

Common causes

  • Signal wire shorted to ground (chafed upfitter wiring is common)
  • Failed selector switch/potentiometer shorted internally
  • Open reference/supply voltage to the selector
  • Coolant, water, or corrosion bridging terminals in an exterior-mounted selector or connector
  • Miswired upfitter circuit grounding the input

Common misdiagnoses

  • Replacing the PCM
  • Replacing the PTO unit or control solenoid
  • Replacing selector 1 components when the fault is on circuit 2

Troubleshooting steps

  1. 1.Confirm the stuck-low signal

    Key on: the input PID or backprobed signal voltage near 0V in every selector position confirms circuit-low rather than a rationality issue.

  2. 2.Unplug the selector and re-check

    If the signal rises to reference voltage with the selector disconnected, the wiring is intact and the selector itself is shorted — replace it.

  3. 3.Verify the reference supply

    Measure the expected supply (commonly 5V) at the selector connector; a missing reference makes the signal read low and points upstream to the harness or a shared-circuit short.

  4. 4.Isolate a harness short to ground

    With both ends disconnected, resistance from the signal wire to chassis ground should exceed 10k ohms; near 0 ohms means the wire is chafed through, so inspect where upfitter wiring crosses frame edges and clamps.

  5. 5.Repair and verify full function

    After the repair, sweep the selector through all positions on live data and run the PTO to confirm commanded speeds are reached without the code resetting.

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