P099B
Shift Solenoid G Control Circuit Low
Transmission
Generic OBD-II
Medium
What it means
P099B means the transmission control module detected low voltage on the shift solenoid "G" control circuit, typically from a short-to-ground or a failed solenoid. Shift solenoids control gear engagement, so this fault usually causes rough or harsh shifting and can trigger limp mode. The engine starts and runs normally; the problem is inside the transmission's control system.
Medium
Can I keep driving? Usually drivable, but expect rough shifts and possible limp mode; repair soon to avoid transmission damage.
Common symptoms
What you'll notice
- Check-engine light on
- Very rough or harsh gear shifting
- Slipping or failure to engage certain gears
- Transmission may drop into limp (fail-safe) mode
Common causes
Most likely first
- Failed shift solenoid GLikely
- Low or dirty/contaminated transmission fluidCommon
- Poor electrical connection or shorted wiring in the solenoid G circuitCommon
- Faulty valve body assemblyLess often
- Faulty transmission control module (TCM)Less often
How to diagnose & fix
Work through it in order
- Check transmission fluid level and condition; top up or service if low, burnt, or dirty.
- Inspect the solenoid G wiring and connector for a short-to-ground or corrosion.
- Measure solenoid resistance and control-circuit voltage against spec.
- Replace shift solenoid G if it tests out of range.
- If the solenoid and wiring are good, inspect the valve body and have the TCM diagnosed. Clear and road-test.
FAQ
Quick answers
Is it safe to drive with P099B?+
Short trips are usually possible, but rough shifting and limp mode add wear, so get it repaired soon.
Can I just clear P099B?+
It returns as soon as the circuit reads low again; clearing only confirms a completed repair.
Related codes
Often seen with P099B
Read & clear P099B 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