P078A
Shift Timing Solenoid B
Transmission / shift controls
Generic OBD-II
Medium
What it means
P078A means the transmission control module detected a fault in the shift timing solenoid B circuit. This solenoid influences how and when gear changes occur, so a fault can make shifts feel rough or poorly timed and may trigger limp mode. The cause is usually the solenoid or its wiring, though fluid condition and the valve body are worth checking too.
Medium
Can I keep driving? Usually drivable, but shifts may feel rough or poorly timed and the transmission can drop into limp mode — have it fixed to avoid extra wear.
Common symptoms
What you'll notice
- Rough or poorly timed gear shifts
- Harsh or delayed engagement
- Possible limp mode (fixed gear)
- Check-engine light on
Common causes
Most likely first
- Faulty shift timing solenoid BLikely
- Wiring or connector fault in the solenoid circuitCommon
- Low or dirty transmission fluidCommon
- Stuck or worn valve bodyLess often
- Failed transmission control module (TCM)Less often
How to diagnose & fix
Work through it in order
- Check transmission fluid level and condition.
- Inspect the shift timing solenoid B connector and wiring for damage or corrosion.
- Electrically test the solenoid and compare to spec.
- Inspect the valve body passages the solenoid controls.
- Replace the solenoid if faulty; evaluate the TCM last. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P078A?+
For short trips usually, but shifts may be rough or badly timed. Repair it promptly so poorly timed shifts don't add wear.
Can I just clear P078A?+
You can, but it returns until the solenoid or its circuit is repaired.
Related codes
Often seen with P078A
Read & clear P078A yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX