How long does it take to replace a transmission sensor

What is an automatic transmission gear position sensor?

Automatic transmissions in modern cars and trucks not only tell the driver what drive range the vehicle is in, they must also send this detail to other parts of the auto. The gear position sensor provides this information. This sensor is responsible for communicating the drive range selected by the driver — park, reverse, neutral, drive or one of the lower gear ranges. Among other duties, the sensor prevents the car from being started in any drive range other than park or neutral.

How does an automatic transmission position sensor work?

Usually located inside the transmission, the gear position sensor typically monitors the movement of the shift shaft, which changes when the driver shifts the gear selector lever in the car. Once a drive range is selected, the sensor sends that information to the rest of the vehicle. For instance, the sensor will signal that the engine may be started, and may require the brake pedal to be pressed first. If the vehicle is in reverse, the sensor will send a signal to illuminate the backup lights.

What are the symptoms of a bad automatic transmission position sensor?

When the position sensor fails, the car’s computer won’t know which gear the driver has selected. As a result, the engine will likely fail to start because the computer may not know the transmission is in park or neutral. If the gear position sensor has failed in a way that allows the car to start, only one or two gears will likely be available. Warning lights will likely be lit on the dashboard, and the transmission may not drive in the range selected. This is a dangerous situation, but it’s very unlikely.

Can I drive with a bad automatic transmission position sensor?

Most vehicles become completely useless without a functioning transmission position sensor. Even if the vehicle will drive in limp-home mode, it will be jerky and slow, and consume a lot fuel. You should get to a mechanic as soon as you notice the problem; driving the vehicle will eventually leave you stranded.

How often do automatic transmission position sensors need replacement?

Many automatic transmission gear position sensors will last a long time, and proper maintenance of the transmission can help keep the sensor in good condition. Most vehicles will go to the salvage yard with the same sensor they left the factory with, but these sensors do fail occasionally, and they fail at random.

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.

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