Code Definition

P099B — Shift solenoid G circuit low

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P099B

P099B is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P099B is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P099B is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The fault code P099B is set when the Engine Control Module (ECM) or Transmission Control Module (TCM) detects a low voltage condition in the circuit of shift solenoid G. This solenoid is a vital component in the transmission’s hydraulic system, playing a crucial role in controlling the flow of transmission fluid for gear engagement. A low voltage in the solenoid's circuit can indicate an electrical issue such as a short to ground, insufficient power supply, or poor electrical connection, which may impair the solenoid's functionality. This can lead to problems with gear shifting, including de...

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