A wide array of sensors and modules control your transmission, but what exactly do they do and how do they lead to symptoms of transmission failure? In many cases, there may be at least ten different modules that directly or indirectly control and provide feedback to your transmission. The number of modules that vehicles use depends on their complexity. Below is a list of various modules
and sensors that regulate your automatic transmission. Please note that problems and their causes vary relative to specific makes and models – these are simply the most common. Learn More
All automatic transmissions use a control module to regulate speed, gear changes, and clutch engagement. The TCM makes decisions based on the information it receives from the engine, making it the key to shifting gears and changing the speed. A TCM recognizes when the clutch is engaged and disengaged and reads RPMs, then executes an order based on driver feedback. Some modules have an internal memory that
will recall your driving habits and apply that data to your transmission’s performance. A powertrain control module also controls engine and transmission functions. It is responsible for timing shifts, shift feel, and engaging the clutch. When your PCM fails, your transmission is likely to stop shifting, shift too soft or harsh or cause complete transmission failure. Bad transmission control module symptoms:
Mass Airflow Sensor (MAS)The Mass Airflow Sensor measures airflow into the engine and uses that information to regulate air and fuel ratios and determine engine load. Symptoms of a bad mass airflow sensor:
Throttle Position Sensor (TP)The Throttle Position Sensor measures throttle (gas pedal) position, having a direct impact on engine performance. Symptoms of a bad throttle position sensor:
Manifold Absolute Pressure Sensor (MAP)The Manifold Absolute Pressure Sensor measures manifold pressure. It’s used to measure engine load. It also measures altitude and controls engine performance. Symptoms of a bad manifold absolute pressure sensor:
Intake Air Temperature Sensor (IAT)The Intake Air Temperature Sensor measures the temperature of the air while it enters the intake of the engine. It’s used to control the air/fuel mixture of the engine. It’s also part of the pressure control system for the transmission. As temperature changes, so do the sensor’s electrical resistance and voltage signal. Symptoms of a bad intake air temperature sensor:
Differential Speed Sensor (DSS)The Differential Speed Sensor measures vehicle speed. Failure may inhibit activation of overdrive and the converter clutch. Symptoms of a bad differential speed sensor:
Overdrive Switch (OD)Overdrive is a function that allows you to cruise at a sustained speed, but reduced engine rpm. This provides better fuel economy, lower noise, and reduced wear on mechanical components. Engaging and disengaging overdrive requires a switch. When this switch fails transmission problems occur. Symptoms of a bad overdrive switch:
Vehicle Speed Sensor (VSS)The Vehicle Speed Sensor measures vehicle speed. When it fails the transmission can stop shifting or shift late and harsh. A bad VSS may also inhibit overdrive and the converter clutch. Symptoms of a bad vehicle speed sensor:
Air Conditioner Sensor (AC)The Air Conditioner Sensor signals the PCM when the air condition is on or off. The AC switch will affect engine RPM at a stop. A malfunctioning AC switch can result in problems that feel as though they are transmission related. Transmission Range Sensor (TR)/ Transmission Position SensorThe Transmission Range Sensor tells the PCM the position of the transmission shifter. The PCM uses this information to control which gears of the transmission to enable or disable. When the TR sensor fails it can cause wrong gear starts, no upshifts, or what feels like a falling-out-of-gear condition. Symptoms of a bad transmission range sensor:
Brake SwitchThe Brake Switch measures brake pedal position. Its primary function is to release the converter clutch while braking. When it fails the converter clutch won’t apply, or it may chuggle while coming to a stop. Symptoms of a bad brake switch:
Coolant Temperature Sensor (CT)The Coolant Temperature Sensor measures engine coolant temperature. It’s used to inhibit overdrive and the converter clutch when the engine is too cold. Failure will severely impact engine performance. Symptoms of a bad coolant temperature sensor:
Turbine Shaft Sensor (TSS)The Turbine Shaft Sensor measures input shaft speed. The PCM uses the information provided by the TSS to determine whether or not the transmission is slipping. When it fails it usually results in shift timing problems. Depending on the manufacturer, it can cause multiple shift-timing and shift-feel problems. Symptoms of a bad turbine shaft sensor:
Transmission Fluid Temperature Sensor (TFT)The Transmission Fluid Temperature sensor measures the temperature of the transmission oil (AFT). Its primary function is to inhibit overdrive and converter clutch operation when cold. On some models, it also inhibits certain gears based on the temperature (too hot or too cold). Symptoms of a bad transmission fluid temperature sensor:
Connect with General TransmissionIf you have any questions regarding a transmission failure, repair or remanufacture, give transmission shops in Reno a call today. General Transmission is a family owned transmission repair shop built on values and integrity and we’re more than happy to answer your questions. Schedule a Transmission Failure Repair Today!Schedule a Repair Can a faulty sensor cause shifting issues?Therefore, a failing speed sensor will have a direct impact on automatic transmission operation. One of the most common signs of a bad speed sensor is abnormal automatic transmission operation. If the VSS is faulty, the transmission may exhibit symptoms such as delayed shifts, hard shifts, and limited gear operation.
Can a sensor make your transmission not shift right?A failing transmission position sensor may no longer send the right signals to the Powertrain Control Module, or PCM. Without signals from the position sensor, the PCM will no longer know when to shift the transmission's gears out of park into a moving gear. Transmission shifts into the wrong gear.
Can transmission speed sensor cause shifting problems?Harsh or Improper Shifting
Without a valid speed signal from these sensors, the PCM will not be able to correctly control the shifting of gears within the transmission. This may cause the transmission to shift roughly or more quickly than normal.
Which speed sensor controls the transmission?Typically, two sensors communicate the transmission data to the vehicle's powertrain control module. The first sensor, referred to as the input sensor, monitors the speed of the transmission's input shaft. The second sensor is the output sensor, which monitors the output shaft speed.
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