P099C
Shift Solenoid G Control Circuit High
Transmission controls
Generic OBD-II
Medium
What it means
P099C means the transmission control module detected higher-than-expected voltage in the shift solenoid 'G' control circuit, usually from an open or high-resistance wiring fault or a failed solenoid. It typically causes rough shifting or a limp-mode condition; the engine itself still starts and runs.
Medium
Can I keep driving? Usually driveable, but shifting may be rough and the transmission can enter limp mode — repair it before it adds wear.
Common symptoms
What you'll notice
- Check-engine light on
- Rough or harsh gear shifting
- Transmission slipping or holding a gear
- Transmission stuck in a limited-gear limp mode
Common causes
Most likely first
- Open circuit or high resistance in the shift solenoid 'G' wiringLikely
- Failed shift solenoid 'G'Common
- Loose or corroded electrical connectorCommon
- Valve body or internal fault affecting the solenoidLess often
- Faulty transmission control module (TCM) — less commonLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and inspect the solenoid 'G' connector and wiring for an open or high resistance.
- Check transmission fluid level and condition; low or contaminated fluid can affect solenoid operation.
- Measure the solenoid circuit resistance and test the solenoid; replace it if out of spec.
- If the circuit and solenoid are good, inspect the valve body and have the TCM evaluated. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P099C?+
Short trips are usually possible, but shifting may be rough or the transmission may limp. Repair it soon to avoid extra wear.
Can I just clear P099C?+
The code returns once the high-voltage circuit condition reappears. The wiring or solenoid fault must be repaired.
Related codes
Often seen with P099C
Read & clear P099C 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