P28D9
Clutch B Motor Underspeed
The clutch B actuator motor falls below the calibrated minimum speed for the commanded duty. High mechanical load or supply voltage low.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Common causes
Ordered by how often each turns out to be the cause.
- Mechanical load increased (binding)Common
- Supply voltage low under loadPossible
Parts involved
- Clutch Motor B
- Clutch Actuator B
P28D9 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.