OBD-II fault code

P099B: Shift Solenoid G Control Circuit Low

What it means

The control module detects a low electrical level in the shift solenoid G control circuit.

At a glance

  • Usually lights the check-engine light
  • The engine or gearbox may go into limp mode

How it works

Shift solenoid G is an electrically operated valve used to control transmission fluid flow during shifting. This code sets when the control module sees a lower electrical level than expected in the solenoid G control circuit, commonly from a short to ground or a shorted coil.

Common causes

Most likely first.

  1. Control wire shorted to ground
  2. Internal short in coil
  3. Connector pins corroded - high contact resistance

Symptoms

  • Check engine or transmission warning light on
  • Harsh, delayed, or missing shifts
  • Possible limp mode (locked in one gear)
  • Slipping or shuddering during gear changes

How to diagnose it

  1. Save freeze-frame data and check live transmission data for solenoid G commands and shift symptoms at the time of the fault.
  2. Inspect the solenoid G connector and harness for rubbed-through insulation, fluid intrusion, corrosion, or damaged terminals that could ground the circuit.
  3. Use the wiring diagram and manufacturer's procedure to test the solenoid G control wire for a short to ground.
  4. Measure the solenoid G coil and circuit as specified by the manufacturer to identify a shorted coil or abnormal resistance.
  5. If the wiring and solenoid pass, test the control module output and grounds according to the manufacturer's procedure.

Common fixes

  • Repair the solenoid G control wire if it is shorted to ground.
  • Clean or repair corroded or damaged terminals at the solenoid G connector.
  • Replace shift solenoid G if its coil tests shorted or outside specification.
  • Repair the solenoid G harness if testing finds an intermittent or high-resistance connection.
  • Repair or replace the control module only if tests confirm it is causing the low circuit condition.

Can I keep driving?

Avoid towing or hard acceleration, and stop driving if the transmission slips badly or cannot select gears reliably. A low solenoid G circuit can disrupt shifting, and continued slipping may cause further damage.

A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together

This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.

Codes for the same component