Powertrain, generic (extended)

P28C5 Clutch A Motor Phase U-V-W Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

With P28C5 the controller finds one or more phases of the clutch A motor sitting higher than the switching pattern allows, as if a lead were tied to battery voltage. The motor in question is the brushless drive of an on-demand pump actuator: Getrag introduced this concept with the 7DCT300, where one motor per clutch turns a gerotor pump and the pump pressure itself closes the clutch. Causes on the high side are a phase touching a supply wire in the harness, moisture bridging pins in the connector, or an output transistor that no longer switches off. Unlike P28C4 the fault points away from ground. Thresholds are not published by any manufacturer. The transmission typically drops clutch A and runs on the remaining shaft.

Likely causes

Motor phase lead shorted to a supply line in the harness
Moisture or corrosion bridging pins at the actuator connector
High-side switch in the controller that no longer turns off

Symptoms

  • Warning lamp for the transmission and stored DTC
  • Half of the gear set unavailable, vehicle continues with reduced choice
  • Clutch A may not open or close on command

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

P28C4P28C6P28C7P28D3

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