P078C
Shift Timing Solenoid B Low
Transmission
Generic OBD-II
Medium
What it means
P078C means the transmission control module detected a low-voltage (often a short-to-ground) condition in the shift timing solenoid B circuit. This solenoid helps control when shifts happen, so a fault can make shifts feel rough or badly timed. The usual causes are wiring shorted to ground, a failed solenoid, or a connector problem.
Medium
Can I keep driving? The car will usually still drive but shift timing may feel off or harsh — drivable short-term, but have the circuit checked before it worsens.
Common symptoms
What you'll notice
- Check-engine light on
- Rough, poorly timed, or harsh gear shifting
- Delayed or inconsistent shifts
- Possible limp (fail-safe) mode
Common causes
Most likely first
- Short to ground or low-voltage fault in the shift timing solenoid B circuitLikely
- Failed shift timing solenoid BCommon
- Damaged, chafed, or corroded wiring/connectorsCommon
- Low or contaminated transmission fluidLess often
- Failed transmission control module (TCM)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check transmission fluid level and condition first.
- Inspect the solenoid connector and wiring for shorts to ground, chafing, or corrosion.
- Measure the solenoid circuit voltage and resistance against spec; a low reading points to a short or shorted solenoid.
- Test and replace shift timing solenoid B if it's out of spec.
- If the circuit and solenoid are good, evaluate the TCM. Clear and road-test.
FAQ
Quick answers
Is it safe to drive with P078C?+
Short trips are usually okay, but shift timing may be off and the transmission can enter limp mode. Get it diagnosed before it causes extra wear.
Can I just clear P078C?+
It returns as soon as the low-voltage condition recurs in the solenoid circuit. The wiring or solenoid still needs repair.
Related codes
Often seen with P078C
Read & clear P078C 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