What does it mean?
SPECIAL NOTES: Non-professional mechanics are strongly urged NOT to attempt a diagnosis and/or repair of code P0909 – “Transmission gate select control error” without first reading the section in the manual for the affected application that deals with gear selection. Failure to gain at least a working knowledge of the gearshift mechanism and its control circuit will almost certainly result in confusion, a misdiagnosis, and quite possibly, irreparable harm to the mechanism and its control system.
Also note that design specifics of components, as well as testing/diagnostic procedures for code P0909 vary greatly between applications and manufacturers. For this reason, the information in this guide is intended for general informational purposes only, and it should therefore NOT be used in any diagnostic procedure for this code on ANY application without making proper reference to the manual for the affected application. END OF SPECIAL NOTES.
OBD II fault codeP0909 is a generic code that is defined as “Transmission gate select control error”, or sometimes as “Transmission Shift Change Actuator Neutral Position Learned Value out of Range”. Regardless of the actual wording of the definition, this code is set when the PCM (Powertrain Control Module) detects a problem in the gear shift selector mechanism or its control circuit.
Note that this code only applies to automated manual transmissions (also sometimes known as multi-mode transmissions), which are normal manual transmissions that have been fitted with automated, computer-controlled gear selection mechanisms. While the design specifics of automated gear selection mechanisms vary between manufacturers, such systems usually consist of electrically or sometimes hydraulically operated actuators, control linkages/rods, position sensors, and input and feedback circuits.
In automatic mode, the PCM determines appropriate shift points based on input data from various engine and driveability sensors. When a shift point is reached, the PCM will actuate the clutch (which is a normal manual transmission clutch), and actuate the gear shift actuators to deselect the current gear, and then to select the desired gear ratio.
Each de-selection/selection is monitored by position sensors, and should the PCM detect that the actual position of the gearshift mechanism does not agree with the desired position, it will set code P0909, and may also illuminate a warning light. Note that on some applications, multiple failure cycles need to occur before the PCM will illuminate a warning light. The image below shows one example of the typical layout/construction of a gear shift mechanism.
Note though that the appearance, construction, and operation of these mechanisms vary between manufacturers, and proper reference to the manual for the affected application MUST be made to determine the appropriate testing and possible repair methods that apply to that application.