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Q: Transmission problem

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I have a 2003 Nissan Sentra - Auto Transmission - with about 95,000 miles. Recently it has been having trouble shifting into higher gears (like it is stuck in first gear). When I turn off the car and turn it back on the problem is fixed for the rest of the trip (usually). Also, the "check engine soon" light is on and we have already tried replacing the speed sensor, my mechanic said that could be an electrical problem but he cant find, Is there anything else we can try other than replacing the transmission? This our mechanic's final suggestion.

My car has 95000 miles.
My car has an automatic transmission.

Hello, This may be a sign of low transmission fluid or a faulty transmission control solenoid. As you’re going down the road, the car’s computer analyzes data being sent by vehicle speed sensors and engine speed sensors. Based on this information, the Engine Control Unit (ECU), or the Transmission Control Unit (TCM), executes the appropriate upshift / downshift by sending a signal to one of several shift solenoids. These transmission solenoids have a spring-loaded plunger inside, which are wrapped with wire. When this coil of wire receives an electrical charge from the TCM / ECU, it causes the plunger to open, allowing transmission fluid to flow into the valve body and pressurize the desired clutches and bands. When this happens, the transmission changes gears and you continue down the road. The car’s computer controls the transmission solenoid in several ways. If the vehicle is equipped with a dedicated Transmission Control Unit, it can open or close the hydraulic circuit using a direct 12v signal. Or, the Engine Control Unit can control the solenoid’s plunger by turning the ground circuit on and off. A solenoid can be used to control a single gear or multiple gears, depending upon the complexity of the design. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your transmission.

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