Powertrain, generic (extended)

P28D9 Clutch B Motor Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28D9 indicates that the clutch B motor cannot reach the speed it is commanded to, leaving the pump short of flow to raise or adjust clutch pressure. Getrag states that its pump actuators control pressure consistently down to low temperatures, so a motor that persistently lags points to extra drag rather than normal cold behaviour: particles caught in the gerotor, a tight bearing, or oil of the wrong grade. Stellantis names jammed actuator pumps on the 7HDT300 in bulletin 21-040-26, but lists P28D5 there, not P28D9. On the electrical side a weak supply or a driver stage that reduces output due to heat, logged as P28D6, can also hold the motor back. Excess speed is P28D8; P28CA is the clutch A version. No threshold is public.

Likely causes

Particles caught in the clutch B gerotor pump
Tight or damaged bearing in the clutch B motor or pump
Incorrect transmission fluid with too high viscosity
Low supply voltage or poor ground at the actuator

Symptoms

  • Delayed or jerky engagement of clutch B
  • Fault more likely after standing in the cold
  • Clutch B gears may be withheld

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,600
Time0.5–4 h

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

Parts involved

clutch motor bclutch actuator b

Related codes

P28D8P28D7P28D6P28DBP28CA

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