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P codepowertrainMedium severity

P087AClutch Position Sensor "B" Circuit

A general electrical fault has been detected in the clutch position sensor "B" circuit, used to track clutch actuator travel on automated manual and dual-clutch transmissions.

Definition

On dual-clutch and automated manual transmissions, clutch position sensors report exactly how far each clutch is engaged so the TCM can modulate launch, creep, and shift handoffs; sensor "B" serves the second clutch (or a redundant channel, depending on design). P087A sets when the TCM detects a general electrical malfunction on this circuit — a signal that is open, implausible, or outside its operating envelope without matching a specific low/high subcode. Expect shuddering or harsh engagements, jerky launches, restricted shifting or limp-home operation on the affected clutch path, and a transmission warning lamp; some vehicles will refuse to drive off until the fault clears.

Common causes

  • Clutch position sensor "B" internal failure
  • Damaged or chafed wiring between the sensor and TCM
  • Corroded or loose connector terminals
  • Loss of sensor reference voltage or ground
  • Clutch actuator wear moving the sensor outside its learned range
  • TCM input circuit fault (rare)

Common misdiagnoses

  • Replacing the entire clutch assembly for engagement shudder
  • Replacing the clutch actuator when only the sensor or wiring has failed
  • Replacing the TCM/mechatronic unit before basic circuit checks
  • Performing repeated clutch adaptations without fixing the circuit

Troubleshooting steps

  1. 1.Read clutch position data on a capable scan tool

    Compare clutch "B" position against commanded position during engagement; a frozen, missing, or wildly jumping value confirms the sensor circuit fault.

  2. 2.Inspect the sensor connector and harness

    Check the clutch actuator/sensor connector for corrosion, fluid intrusion, and chafed wires, especially where the harness flexes with powertrain movement.

  3. 3.Verify reference voltage and ground

    Key on, confirm 4.9-5.1V on the reference pin and less than 0.1V drop on the ground pin at the sensor connector.

  4. 4.Check signal continuity to the TCM

    With both ends disconnected, verify less than about 1 ohm end-to-end on the signal wire and no continuity to ground or power.

  5. 5.Run the clutch adaptation after repair

    Once the circuit is proven good, perform the manufacturer's clutch kiss-point/position relearn so the TCM recalibrates to the sensor, then road test through multiple launches and shifts.

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