Error Code P0909 is defined as Transmission Gate Select Control Error. 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. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another. However, this code only applies to automated manual transmissions (a.k.a. multi-mode transmissions), which are normal manual transmissions fitted with automated computer-controlled gear selection mechanisms.

While design specifics of automated gear selection mechanisms vary from one manufacturer to another, such systems usually are comprised of electrically or hydraulically operated actuators, control linkage or rods, feedback and input circuits, and position sensors.

The Powertrain Control Module (PCM) determines the correct shift points based on the engine and drivability sensors’ data in the vehicle’s automatic mode. The PCM actuates the clutch (normal transmission clutch) each time a shift point is reached. This also actuates the gear shift actuators to deselect the current gear and then select the correct gear ratio. The position sensors monitor each selection (de-selection). If the PCM determines that the gearshift mechanism’s actual position doesn’t correspond to the desired position, it will set the Error Code P0909. This will also activate the Check Engine light. However, on some applications, the vehicle may have to go through multiple failure cycles before the Check Engine light lights up.

Other clutch-related codes that may appear:

  • Error Code P0904
  • Error Code P0905
  • Error Code P0906
  • Error Code P0907
  • Error Code P0908

Common Symptoms

  • Harsh, erratic, unpredictable shifting
  • Stuck transmission (in one gear, some gears may not engage/disengage)
  • Clutch slippage
  • Engine misfire

Possible Causes

  • Faulty gear selection assembly
  • Faulty position sensors
  • Faulty actuators
  • Misaligned control linkages
  • Damaged control linkages
  • Mechanical failure on transmission or clutch
  • Burnt, damaged, disconnected, shorted connectors or wirings
  • Faulty PCM (rare)

How to Check

Connect the OBD-II scanner to retrieve the freeze-frame.

If other codes are present, note the order in which they were stored. Resolve codes that precede Error Code P0909, especially if there are different codes related to the clutch position sensor or clutch actuator. Failure to do so may result in a misdiagnosis or unnecessary repair and replacement of perfectly-fine components.

Refer to the manual to locate the gear shift mechanism; inspect and look for signs of damage, including its related components. Look for signs of water intrusion, damage, etc.

Check all related electrical wirings and connectors (tightness and condition). Replace damaged components as needed. Replace with OEM parts to ensure proper operation.

If you find no damage, then perform a continuity, ground integrity, and resistance test (where applicable, voltage test) on all related wirings. During the controller resistance test, Make sure you disconnect all wires from the PCM to prevent damage to the controller.

Note: Don’t test circuits if you are unsure what the circuit does or how it works. Make sure to refer to the manual.

Inspect the circuits related to the position sensors and internal resistance of all position sensors since resistance value is always a good indicator for the overall condition of the sensor. Replace damaged and faulty position sensors with OEM parts whose internal resistance doesn’t match the manufacturer’s specifications in the manual (closely, or exactly).

If all electrical values check out, activate all actuators using the scanner multiple times to rule out an intermittent problem. Check the status of each actuator when activated, replace those that are slow or did not react.

Some vehicles have their actuators incorporated right into a single gear shift mechanism assembly, which could also house one or more position sensors. If this is the case, the best option is to replace the entire assembly, as repairs can be either extremely expensive or impossible.

After each repair, make sure you clear the codes and take the vehicle for a test drive to see if the code comes back. If the code returns, you can suspect an intermittent fault or a faulty PCM. The former is the likely problem, though, so make sure you repeat and conduct electrical tests thoroughly until you figure out the problem. Always refer to a manual.

Better yet, take your vehicle to a certified technician for a professional diagnosis or repair.

How to Fix

  • Replacement of faulty transmission fate selector position switch
  • Repair or replacement of damaged wires or connectors
  • Correction of switch alignment or adjustment

In most cases, new components and parts require relearning relating to the gear selection mechanism. Always refer to the manual for the relearning details. You may need professional assistance on this one.

It is strongly advised to seek professional help when diagnosing and repairing this error code.