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P codepowertrainMedium severity

P087CClutch Position Sensor "B" Circuit Low

The clutch position sensor "B" circuit voltage has dropped below its valid range, usually from a short to ground or a failed sensor.

Definition

The TCM feeds the clutch position sensor "B" a regulated reference and reads its output to know precisely where the clutch is between fully released and fully applied. P087C sets when that signal falls below the minimum calibrated voltage — evidence of a signal wire shorted to ground, a shorted sensor element, or a collapsed reference supply. Because the TCM can no longer trust the clutch position, it typically restricts or disables that clutch path, producing harsh or refused engagements, limp-home operation on a dual-clutch transmission, and a transmission warning lamp or MIL.

Common causes

  • Signal wire shorted to ground through chafed insulation
  • Clutch position sensor shorted internally
  • 5V reference supply pulled low by a shorted sensor sharing the circuit
  • Fluid or moisture in the connector bridging the signal to ground
  • Crushed or pinched harness near the actuator
  • TCM input circuit failure (rare)

Common misdiagnoses

  • Replacing the clutch actuator when only the sensor circuit is shorted
  • Replacing the clutch assembly
  • Replacing the TCM/mechatronic unit for a wiring fault
  • Repeated adaptations without repairing the circuit

Troubleshooting steps

  1. 1.Confirm the signal is railed low

    Back-probe the sensor signal wire key-on; a reading near 0V that never moves while the actuator is commanded confirms the low-circuit fault.

  2. 2.Unplug the sensor to isolate it

    If the signal wire voltage recovers to the pull-up/reference level with the sensor disconnected, the sensor is shorted; if it stays at 0V, the harness or module is at fault.

  3. 3.Test the signal wire for a short to ground

    With the sensor and TCM disconnected, measure signal-to-ground resistance; anything but open (OL) means chafed wiring, so inspect clamp points and areas near moving driveline components.

  4. 4.Verify the reference supply

    Confirm 4.9-5.1V at the reference pin; if low, disconnect other sensors on the shared 5V bus one at a time to find the component dragging it down.

  5. 5.Repair, relearn, and verify

    After the circuit repair, run the clutch position adaptation and confirm measured position tracks commanded position smoothly through several engagements.

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