Powertrain, generic (extended)

P28D8 Clutch B Motor Overspeed

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P28D8 sets when the clutch B motor spins faster than the controller expects for the commanded pressure. A gerotor works by positive displacement, the EVS32 model uses one with a seven-tooth outer rotor, so in a sealed clutch circuit its speed should fall once pressure is built; a motor that keeps accelerating means oil is escaping or the pump has lost its load. Plausible reasons are a worn piston or rotary seal in the clutch B circuit, aeration from low oil, or a sheared drive between motor shaft and inner rotor. A false speed reading from the rotor position sensor can mimic the same, so P28DA and P28DB should be cleared first. Slow running is P28D9; on clutch A the code is P28C9. No limits are published.

Likely causes

Worn piston or rotary feedthrough seal letting oil escape from the clutch B circuit
Aerated oil due to low level, pump runs without load
Sheared drive between clutch B motor shaft and inner rotor
Rotor position sensor reporting an excessive speed

Symptoms

  • Clutch B does not hold full torque, flaring on shifts
  • Transmission warning and limited gears

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–2,000
Time0.5–6 h

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

Parts involved

clutch motor bclutch actuator b

Related codes

P28D9P28D7P28DAP28DBP28C9

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