Powertrain, generic (extended)

P28C4 Clutch A Motor Phase U-V-W Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28C4 means the transmission controller finds the voltage too low on a phase lead (U, V or W) of the electric motor that operates clutch A. This layout belongs to wet dual-clutch gearboxes without a valve block, such as the Getrag/Magna 7DCT300 and its hybrid derivative 7HDT300: a brushless motor per clutch spins a gerotor pump that feeds oil directly to the clutch piston. A phase pulled towards ground, for example by chafed insulation or a shorted driver transistor, is the typical trigger. P28C5 covers the opposite direction, P28C6 an interrupted phase. No manufacturer publishes a code-specific threshold; the driver loses the gears carried by clutch A and gets a transmission warning.

Likely causes

Phase wire to the clutch A motor chafed through and touching ground
Winding inside the clutch A motor shorted to the housing
Defective output transistor for the motor phases in the transmission controller

Symptoms

  • Transmission warning lamp, often together with the MIL
  • Odd or even gears locked out, depending on which shaft clutch A serves
  • Jerky or delayed pull-away

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,200
Time0.5–3 h

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

Parts involved

clutch motor awiring harnesstcm

Related codes

P28C5P28C6P28C7P28D1P28D2

References: law.cornell.edu, cti-symposium.world, static.nhtsa.gov.