'Shift timing solenoid' means different parts: on GM's 4L60-E the 3-2 downshift solenoid that times the band apply on that downshift, on Aisin five-speeds (GM, Saab) the linear valve SLS that sets clutch pressure during the shift, and on the 2017–18 Genesis G80/G90 with shift-by-wire the on/off solenoids that engage drive (A) and reverse (B). P078A is the general circuit code for solenoid B. The only documented user is Hyundai/Genesis: on the 2017–18 G80/G90 with shift-by-wire it is the on/off solenoid that engages reverse. The bulletins replace valve and electronic module, then the transmission module if the code returns. Reverse may not engage, with warning lamp and limp mode.
Medium severity. Can I keep driving?Drive little and gently. If you hear timing chain noise or the oil light comes on, shut off the engine.
Symptoms
- Warning lamp
- Reverse cannot be engaged (Genesis shift-by-wire)
- Limp mode
Most likely causes
- Solenoid faulty
- Electronic module or transmission module
- Connector or wire
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It can trigger limp mode.
- It affects emissions.
What each character of P078A means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 7: Transmission
- 8A: Specific fault in that system
Frequently asked questions
Can I keep driving with code P078A?
Drive little and gently. If you hear timing chain noise or the oil light comes on, shut off the engine.
What causes code P078A?
The most common causes are: solenoid faulty; electronic module or transmission module; connector or wire.
Related codes
- P0785Shift Timing Solenoid A
- P078BShift Timing Solenoid B Range/Performance
- P078CShift Timing Solenoid B Low
- P078DShift Timing Solenoid B High
- P078EShift Timing Solenoid B Intermittent
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.