How are automatic transmission position sensor issues diagnosed?
Most cars that have a transmission position sensor will show on the dash which gear the vehicle is in. If changing gears does not change what is shown on the display, or if the display is blank or intermittent, the gear position sensor is the primary suspect. But because the problem could also be a fault in the transmission control module, powertrain control module or wiring harness, a physical inspection will likely be conducted, followed by a scan test of the position sensor. If the sensor is sending false readings, no readings or intermittent readings, the sensor harness will be physically tested in order to read its outputs. The reference voltage, battery voltage and grounding will be checked, as well. If the sensor is receiving proper voltage but sending bad information, the selector shaft sensor will be checked for physical damage and poor connections before the sensor is declared faulty.
How are automatic transmission position sensors replaced?
On some models, manufacturers have started placing the sensor on the transmission’s exterior, but on many, the sensor is on the inside, connected to the valve body, shift shaft, or both. In a worst-case scenario, the shift shaft assembly, transmission pan and valve body may need to be removed in order to get to the gear position sensor. Once accessed, the sensor can be removed and replaced, and any obstructing components can be replaced as well. The shift shaft should receive a new seal before installation, and the transmission pan, filter, pan gasket and fluid should be replaced prior to test-driving the vehicle.
RepairPal recommendations for automatic transmission position sensor issues
When servicing a failed automatic transmission gear position sensor, we also strongly advise servicing the transmission if maintenance has been lacking. This goes doubly if the transmission gear position sensor is located inside the transmission. When the repair is completed, the sensor will operate as normal, but if contamination was the root cause of the failure, the transmission control unit can receive more precise information if the transmission fluid and filter are also changed.
What to look out for when dealing with automatic transmission position sensor issues
For a physically damaged internal gear position sensor, the transmission and torque converter should be completely drained of fluid, and a thorough inspection of the transmission should be performed. Also, a follow-up transmission service can ease concerns of particulate matter from the sensor floating through the moving parts of the transmission.
Can I replace the automatic transmission position sensor myself?
If the gear position sensor is on the outside of the transmission housing, replacement is a snap. But internal sensors should only be replaced by a professional technician or a very experienced DIYer. There are many components that may be damaged while inside the transmission pan, especially if the valve body has to be removed. If the job involves removing the transmission pan, have a certified shop handle the repair.