Powertrain, generic (extended)

P28CB Clutch A Motor Position Sensor Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

A brushless motor can only be commutated correctly if the electronics know where the rotor stands; P28CB reports that the signal from the sensor tracking the clutch A motor's rotor position is missing or electrically unusable, mostly through an open line. Without it the controller cannot switch the U-V-W phases in the right order or count motor revolutions, so the pump of clutch A is shut down. In Getrag-type pump actuators these brushless ferrite motors are shared parts, and the position signal also serves to check motor speed against the pressure target. Typical causes: an open sensor feed or ground, a corroded pin, a failed sensor element. P28CC covers a signal that is present but implausible. No manufacturer publishes P28CB details.

Likely causes

Open signal, supply or ground wire of the clutch A motor position sensor
Corroded or loose pin at the actuator connector
Failed position sensor inside the actuator

Symptoms

  • Clutch A disabled, gears on that shaft unavailable
  • Transmission warning lamp
  • Possibly also motor speed codes stored

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,200
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

clutch motor position sensor awiring harnesstcm

Related codes

P28CCP28C9P28CAP28DA

References: law.cornell.edu, cti-symposium.world.