Error Code P0931 is defined as Gear Shift Lock Solenoid Circuit “A” High. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to the present. Of course, specifications on the definition, troubleshooting, and repairs vary from one make and model to another.

When this code appears, that means there is a reading problem in the gear shift lock solenoid circuit.

The gear shift lock solenoid works by making sure the Park position of the gear does not move out of position unless the brake pedal is pressed. This means the gear can shift from Park to Drive or Reverse when the brake pedal is deployed. If the powertrain control module (PCM) detects a high voltage reading in the gear shift lock solenoid circuit, it registers this error code.

Common Symptoms

  • Gear unable to shift out of park
  • Check engine light activated

Fortunately, most modern vehicles with automatic transmission come with a built-in fail-safe that can be accessed via screwdriver.

Possible Causes

  • Faulty gear shift lock solenoid
  • Faulty brake light switch
  • Low battery voltage
  • Damaged electrical components (circuits, connectors, wires)
  • Defective PCM (rare)

How to Check

As with most codes, start the diagnosis by connecting a standard OBD-II code reader to the vehicle. Take note of the freeze frame data from the scanner, gather all registered information, and see if other codes are present. If there are other codes present, take care of them in the order that they appear.

Clear the codes and restart the vehicle to see if the problem comes back. If the problem does not come back, then it may have been triggered erroneously, or it is an intermittent error. If it is the latter, you may have to wait for the problem to progress before accurately and adequately diagnosing it.

If the code comes back, proceed with your diagnosis by inspecting the electrical components of the system. Check for any loose, corroded, open, or shorted wires. Any damaged electrical components must be replaced.

Next, check the battery as well. Make sure it is properly charged.

Then, inspect the gear shift lock solenoid. Test it for continuity. This is the most common culprit of this error code. If the solenoid is working right, then check the brake light switch.

After replacing damaged components, reset the trouble codes, then restart the vehicle to see if the code comes back.

How to Fix

  • Replacement of faulty gear shift lock solenoid
  • Replacement of faulty brake light switch
  • Replacement of faulty circuits, connectors, and wires
  • Recharging or replacement of the battery

This problem does not cause serious damage to the vehicle, but it is an urgent concern since it immobilizes the vehicle.