Powertrain, generic (extended)

P28F4 Engine Disconnect Clutch Pressure Sensor Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

With P28F4 the disconnect clutch pressure sensor sends a voltage above anything it could produce even at full clutch pressure. Typical reasons are a signal line touching the reference or battery supply, an open sensor ground, or on inputs with a pull-up resistor a signal wire that is broken at the sensor. No manufacturer publishes a threshold for P28F4. The sensor matters because the controller closes the clutch by pressure: Ford mounts one on the clutch of its 10R80 hybrid gearbox, while Hyundai notes in a patent that a reading wrongly offset from the real pressure makes the clutch slip. A falsely high value would suggest a firmly closed clutch. CARB obliges the maker to test such inputs against their valid range. P28F3 is the low fault. Most systems stop using the clutch until the fault clears.

Likely causes

Signal wire shorted to sensor reference or battery voltage
Sensor ground open or corroded at the connector
Pressure sensor failed with output stuck high

Symptoms

  • Hybrid or transmission warning light
  • Clutch slips when the engine is meant to drive
  • Electric-only operation or reduced power

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,500
Time0.5–5 h

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

Parts involved

engine disconnect clutch pressure sensorwiring harness

Related codes

P28F1P28F2P28F3P28F5

References: law.cornell.edu, static.nhtsa.gov, patents.google.com.