P078A
Shift Timing Solenoid B
General fault on shift timing solenoid B — second timing solenoid for shift events that need a different ramp profile (typically downshifts vs. upshifts, or specific gear pairs).
- 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.
- Solenoid electrical or hydraulic faultCommon
Parts involved
- Shift Timing Solenoid B
- Valve Body
P078A 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.