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DTC codes / P09xx · Transmission / P0906

P0906Gate Select Position Circuit Low

P0906 indicates that the transmission control module (TCM) has detected an abnormally low voltage on the gate select position circuit, which is used to confirm the position of the gear selector gate. The TCM expects a specific voltage range on this circuit and sets the code when the signal falls below the minimum threshold, often due to a short to ground or an open circuit.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light
  • Transmission may enter limp mode or fail to shift properly
  • Difficulty moving the gear selector or selecting gears
  • Erratic or delayed gear engagement
  • Often no symptoms besides the warning light

Common causes, most likely first

  1. Faulty gate select position sensor or switch
  2. Damaged or corroded wiring harness in the gate select circuit
  3. Poor electrical connection at the sensor or TCM
  4. Short to ground in the signal circuit
  5. Failed transmission control module (TCM)
  6. Internal transmission mechanical issue affecting the gate select mechanism

How to diagnose and fix it

  1. Use a scan tool to retrieve all stored codes and freeze-frame data to confirm P0906 is active.
  2. Visually inspect the gate select position sensor and its wiring for damage, corrosion, or loose connections.
  3. Disconnect the sensor and check for reference voltage and ground at the connector with a multimeter.
  4. Perform a continuity test on the signal circuit between the sensor and TCM to check for opens or shorts to ground.
  5. If the circuit tests good, test the sensor's resistance or voltage output through its range of motion; replace if out of specification.
  6. Check TCM connectors for corrosion or water intrusion and repair as needed.
  7. If all external circuits and components are good, follow the manufacturer's diagnostic flow for TCM testing or replacement.

Gate select circuit checks that techs often skip

  • A short to ground in the gate select signal circuit can be caused by a pinched wire under the center console or near the shifter assembly, which is easy to overlook during a visual inspection.
  • The gate select position sensor is sometimes integrated into the shifter assembly and not sold separately, so technicians should verify part availability before condemning the sensor.
  • P0906 can be set intermittently by a loose ground connection at the transmission or chassis, so checking ground straps and battery terminals is a wise first step.
  • On some vehicles, the gate select signal is shared with other systems, and a fault in a related module can cause a low voltage reading on this circuit even if the sensor itself is good.
  • A low voltage on the gate select circuit does not always mean the sensor has failed; a simple chafed wire or corroded connector is a more common root cause.

Can I keep driving with P0906?

If the vehicle drives and shifts normally, you can drive it to a repair shop, but avoid aggressive acceleration or heavy loads. If the transmission is in limp mode or shifting erratically, stop driving and have it towed to prevent further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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