Sensing the Power: A Comprehensive Guide to Automatic Transmission Sensors

Your automatic transmission has many sensors that help it work smoothly and efficiently. Sensors are devices that sense or measure something and send signals to the computer. The sensors in your automatic transmission sense the speed, temperature, pressure, and position of the parts and the fluid in your transmission. They send signals to the transmission computer, which uses the information to make your transmission change gears, lock up, and cruise.

In this article, we will tell you about the different types of sensors in your automatic transmission and what they do. We will also tell you why it is important to understand how the sensors work for fixing and preventing problems with your transmission.

Speed Sensors

Speed sensors are devices that measure how fast something is spinning. They use a magnet or a light to make an electric signal that matches the speed of the spin. There are three main types of speed sensors in your automatic transmission:

• The input speed sensor is on the input shaft of the transmission, which connects the clutch to the transmission. It measures the speed of the engine and tells the transmission computer how hard the engine is working.
• The turbine speed sensor is on the turbine shaft of the transmission, which connects the torque converter to the transmission. It measures the speed of the turbine, which is the part of the torque converter that is spun by the fluid. It tells the transmission computer how much the torque converter is slipping or locking.
• The output speed sensor is on the output shaft of the transmission, which connects the transmission to the differential. It measures the speed of the output shaft, which is the speed of the car. It tells the transmission computer what gear to choose and when to shift.

Temperature Sensors

Temperature sensors are devices that measure the temperature of a fluid or a component. They use a thermistor, which is a resistor that changes its resistance according to the temperature. There are three main types of temperature sensors in your automatic transmission:

• The transmission fluid temperature sensor is in the transmission pan, which holds the transmission fluid. It measures the temperature of the transmission fluid, which reflects the temperature of the transmission. It tells the transmission computer how to cool or heat the transmission fluid and how to adjust the fluid pressure and the shift time.
• The retarder oil temperature sensor is in the retarder, which is a device that provides extra braking power to the vehicle. It measures the temperature of the retarder oil, which lubricates and cools the retarder. It tells the retarder control module how to cool or heat the retarder oil and how to adjust the retarder operation.
• The transmission oil level sensor is in the transmission pan, which holds the transmission fluid. It measures the level of the transmission fluid, which affects the temperature of the transmission. It tells the transmission computer how to fill or drain the transmission fluid and how to prevent fluid leakage or overflow.

Pressure Sensors

Pressure sensors are devices that measure the pressure of a fluid or a gas. They use a diaphragm, which is a thin membrane that bends according to the pressure. There are two main types of pressure sensors in your automatic transmission:

• The transmission pressure sensor is in the transmission valve body, which is the part that controls the flow of the transmission fluid. It measures the overall pressure within the transmission, which affects the performance and efficiency of the transmission. It tells the transmission computer how to regulate the fluid pressure and the solenoid operation.
• The line pressure sensor is in the hydraulic line, which is the part that carries the transmission fluid. It measures the pressure within the hydraulic line, which affects the shifting and the lockup of the transmission. It tells the transmission computer how to adjust the line pressure and the shift solenoid operation.

Position Sensors

Position sensors are devices that measure the position or the angle of a part or a component. They use a potentiometer, which is a variable resistor that changes its resistance according to the position or the angle. There are four main types of position sensors in your automatic transmission:

• The input shaft position sensor is on the input shaft of the transmission, which connects the clutch to the transmission. It measures the position of the input shaft, which affects the gear selection and the shift timing. It tells the transmission computer what gear the transmission is in and when to shift.
• The output shaft position sensor is on the output shaft of the transmission, which connects the transmission to the differential. It measures the position of the output shaft, which affects the gear ratio and the shift timing. It tells the transmission computer what gear the transmission is in and when to shift.
• The gear selector position sensor is on the gear selector, which is the part that the driver uses to choose the gear. It measures the position of the gear selector, which indicates the gear selected by the driver. It tells the transmission computer what gear the driver wants and how to shift.
• The throttle position sensor is on the throttle body, which is the part that controls the amount of air that enters the engine. It measures the position of the throttle, which indicates the driver’s throttle input. It tells the transmission computer how much power the driver wants and how to shift.

Solenoids: Controlling the Flow of Power

Solenoids are devices that use an electric current to create a magnetic field that moves a metal rod. Solenoids are used to control the flow of hydraulic fluid within the transmission. There are four main types of solenoids in your automatic transmission:

• The line pressure solenoid is in the transmission valve body, which is the part that controls the flow of the transmission fluid. It controls the overall pressure in the transmission, which affects the performance and efficiency of the transmission. It receives the signal from the transmission computer, which tells it how much to increase or decrease the fluid pressure.
• The lockup solenoid is in the torque converter, which is a device that transfers the power from the engine to the transmission using fluid. It controls the lockup of the torque converter, which improves the fuel economy and the performance of the transmission. It receives the signal from the transmission computer, which tells it when to engage or disengage the lockup.
• The shift solenoids are in the transmission valve body, which is the part that controls the flow of the transmission fluid. They control the shifting of the gears, which affects the speed and the power of the transmission. They receive the signals from the transmission computer, which tell them when and how to shift the gears.

Symptoms of Sensor Malfunction: When the Gears Start to Misbehave

The sensors in your automatic transmission are very important for your car’s performance and efficiency. They help your transmission to work smoothly and correctly. However, sometimes the sensors can malfunction or fail, which can cause problems with your transmission. Some of the possible symptoms of sensor malfunction are:

1. Erratic gear changes: Your transmission may shift gears randomly or unpredictably, which can make your ride uncomfortable or unsafe. This can happen if the speed sensors, the position sensors, or the shift solenoids are faulty. They may send wrong signals to the transmission computer, which may confuse it and make it shift gears at the wrong time or in the wrong order.
2. Delayed shifts: Your transmission may take too long to shift gears, which can make your car slow or sluggish. This can happen if the speed sensors, the position sensors, or the shift solenoids are faulty. They may send delayed or weak signals to the transmission computer, which may make it hesitate or miss the optimal shift point.
3. Harsh gear engagements: Your transmission may shift gears too hard or too fast, which can make your car jerk or shudder. This can happen if the speed sensors, the position sensors, or the shift solenoids are faulty. They may send too strong or too frequent signals to the transmission computer, which may make it shift gears too abruptly or aggressively.
4. Check engine light illuminates: One of the more immediate and noticeable symptoms of a problematic sensor in most modern cars is the illumination of the check engine light. The vehicle’s onboard computer triggers this light when it detects issues with the speed sensor, the temperature sensor, the pressure sensor, or the position sensor. This symptom often accompanies other problems like erratic speedometer readings or shift problems.
5. Odd noises when shifting: This is the most common sign of an aging transmission. As the gears shift, you hear lots of banging and clunking noises, which you know aren’t normal. You hear those sounds because something’s moving around inside your transmission that shouldn’t be. This can happen if the speed sensors, the position sensors, the solenoids, or the torque converter are faulty. They may cause the transmission to shift out of sync, to slip, or to lock up, which can create friction and vibration inside the transmission.
6. Reduced fuel economy: Your transmission may use more fuel than usual, which can make your car less efficient and more expensive to run. This can happen if the speed sensors, the temperature sensors, the pressure sensors, or the solenoids are faulty. They may cause the transmission to shift at the wrong time, to stay in the wrong gear, or to lock up when it shouldn’t, which can make your engine work harder and use more fuel.
7. Diminished performance: Your transmission may lose power or speed, which can make your car less responsive and less fun to drive. This can happen if the speed sensors, the temperature sensors, the pressure sensors, or the solenoids are faulty. They may cause the transmission to shift too early or too late, to skip gears, or to lock up when it shouldn’t, which can make your car slower and weaker.

If you notice any of these symptoms, you should take your car to a mechanic as soon as possible. Faulty sensors can reduce your fuel economy, diminish your performance, and even damage your transmission. A mechanic can diagnose and repair your sensors and restore your transmission to its optimal condition.

How to Troubleshoot Sensor Malfunction

If you suspect that your transmission has a sensor problem, you can try to troubleshoot it yourself before taking it to a mechanic. Here are some steps you can follow to diagnose and fix some of the simple sensor problems:

• Check the wiring and the connectors: Sometimes, the sensor problem is not caused by the sensor itself, but by the wiring or the connectors that connect the sensor to the transmission computer. The wiring or the connectors may be loose, corroded, or damaged, which can interfere with the signal transmission. To check the wiring and the connectors, you need to locate the sensor and follow the wires to the transmission computer. You can use a multimeter to test the continuity and the resistance of the wires and the connectors. If you find any problem with the wiring or the connectors, you need to replace or repair them.
• Check the sensor resistance: Sometimes, the sensor problem is caused by the sensor itself, which may have a faulty or worn-out resistor. The resistor is the part of the sensor that changes its resistance according to the speed, temperature, pressure, or position. If the resistor is faulty or worn-out, it may send wrong or no signals to the transmission computer. To check the sensor resistance, you need to locate the sensor and disconnect it from the wiring. You can use a multimeter to measure the resistance of the sensor and compare it to the specifications in your vehicle’s manual. If the resistance is out of range, you need to replace the sensor.
• Check the sensor voltage: Sometimes, the sensor problem is caused by the sensor itself, which may have a faulty or worn-out potentiometer. The potentiometer is the part of the sensor that changes its voltage according to the speed, temperature, pressure, or position. If the potentiometer is faulty or worn-out, it may send wrong or no signals to the transmission computer. To check the sensor voltage, you need to locate the sensor and reconnect it to the wiring. You can use a multimeter to measure the voltage of the sensor and compare it to the specifications in your vehicle’s manual. If the voltage is out of range, you need to replace the sensor.

These are some of the basic troubleshooting steps you can do to diagnose and fix some of the simple sensor problems. However, if you are not confident or experienced in working with electrical components, you should leave the job to a professional mechanic. A mechanic can use more advanced tools and techniques to diagnose and fix the sensor problems, such as a scan tool, an oscilloscope, or a pressure gauge. A mechanic can also check other components that may affect the sensor operation, such as the transmission fluid, the transmission cooler, the transmission valve body, or the transmission computer. A mechanic can also perform a test drive to verify the sensor operation and the transmission performance.

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