Automatic transmissions not shifting into high gear are a serious problem. At present, automatic transmission systems are used in most modern vehicles.
So that the operation of vehicles can be made more smooth and convenient. Because the clutch pedal is not used in automatic transmission systems as it is in manual transmission systems,
But sometimes some kind of fault occurs in the automatic transmission system, due to which there is difficulty in high gear shifting in the automatic transmission.
In this post, we will discuss in detail the reasons for automatic transmissions not shifting into high gear.
What Does ”Automatic Transmission Not Shifting Into High Gear” Mean?
When the automatic transmission is not shifting into a higher gear, it means that the automatic transmission is failing to engage the highest gear available.
Automatic transmissions have many gears, from first gear to high gear. Shifting of these gears is done as per the RPM and requirements of the engine. The purpose of switching to a higher gear is to achieve better fuel efficiency and higher speed at lower engine RPM.
What Is A Automatic Transmission?
Automatic transmissions are an important part of vehicles because they are connected to the vehicle engine and transfer the rotational power of the engine to the drive wheels according to the requirements and condition of the vehicle without manual clutch.
But the workings of automatic transmission are different from manual transmission. Because the automatic transmission system facilitates gear shifts without the need for a manual clutch,
A torque converter is used in automatic transmission systems. In an automatic transmission system, a torque converter connects the engine’s rotational power to the vehicle’s wheels.
Why Does The Automatic Transmission Not Shifting Into High Gear : Causes
If your vehicle’s automatic transmission is not shifting into high gear, the main cause is a low transmission fluid level or leakage. Other causes could be a bad torque converter, a faulty PCM, a damaged shift interlock solenoid, or a faulty transmission sensor.
1. Low Transmission Fluid Level
Most automatic transmission malfunction problems are caused by low fluid levels. because fluid is an important component in an automatic transmission system.
Because in an automatic transmission system, there is no manual clutch like in a manual transmission. because a torque converter is used in an automatic transmission system.
The torque converter transfers the power of the engine to the automatic transmission with the help of transmission fluid. Due to this, the drive wheel of the vehicle is set in motion.
But in an automatic transmission system, the torque converter’s impeller is unable to transfer the fluid to the turbine with full force when the fluid pressure is low.
Due to this, the automatic transmission does not shift into high gear and the automatic transmission of a vehicle stops shifting into any gear. The automatic transmission system may even fail completely, if the fluid level is too low.
2. Faulty Power Control Module (PCM)
Vehicles are equipped with a PCM module to fully control and operate the vehicle’s automatic transmission system. The PCM module controls the automatic transmission function based on signals from sensors located in the automatic transmission.
But sometimes, due to some reason, the PCM module installed in the vehicles gets faulty or some other type of error occurs.
This causes the PCM module to be unable to operate the automatic transmission, or the PCM may initially work fine, causing the PCM to begin to malfunction after the vehicle has been driven for a period of time.
Due to this, there is no problem with the initial gear shifting in the automatic transmission. But the automatic transmission is not able to shift into high gear.
3. Faulty Torque Converter
A torque converter is used instead of a manual clutch in an automatic transmission system. The torque converter transfers the power of the engine to the automatic transmission via transmission fluid.
But sometimes the impeller in the torque converter fails to send the fluid to the turbine during high acceleration, or the turbine is unable to rotate a sufficient amount of fluid during high acceleration.
Due to which the starting gears (1st, 2nd and 3rd gear) of the automatic transmission shift smoothly during low acceleration of the engine.
But at high engine acceleration and high vehicle speed, the torque converter’s impeller and turbine may not engage properly.
Due to this, the automatic transmission does not shift into high gear. A complete failure of the torque converter can result in the automatic transmission failing completely.
4. Damaged Shift Interlock Solenoid
The gear shift interlock solenoid is included in the automatic transmission system. This shift interlock solenoid can cause gear shifting problems in an automatic transmission when it is damaged or malfunctioning.
In an automatic transmission, the shift interlock solenoid locks the gear in the selected position and the PCM module also automatically changes gears in the automatic transmission through the shift solenoid. The automatic transmission shift solenoid helps to shift gears.
But a bad or damaged automatic transmission shift interlock solenoid may also cause the automatic transmission not to shift into high gear.
5. Faulty Transmission Sensor
Automatic transmission systems have input and output sensors to monitor the speed and position of the gears. This sensor sends a gear position and speed signal to the PCM unit in the automatic transmission.
Based on the signal from these two sensors on the automatic transmission system, the PCM unit shifts the gears according to the ratio and speed of the automatic gear.
if any of the sensors in the automatic transmission are faulty. So the PCM will not be able to correctly determine the gear and speed of the automatic transmission.
Therefore, the automatic transmission will not shift into high gear if the PCM does not receive the correct data from the bad automatic transmission sensor. However, this problem can be seen in the shifting of first, second and third gears.
How To Fix ”Automatic Transmission Not Shifting Into High Gear”
To fix the problem of high gear shifting in an automatic transmission, the first thing to do is investigate the cause of the problem.
1. Check & Add Transmission Fluid
In an automatic transmission system, the most common reason for shifting to a higher gear is a low transmission fluid level. So first of all, check the fluid level in the automatic transmission. If the fluid level is low, add transmission fluid. so that the transmission fluid level can be completed.
2. Check & Replace Transmission Sensor
Input and output sensors are installed in the automatic transmission system. monitors the position and speed of gears in an automatic transmission system and sends its signal to PCM.
The PCM automatically changes gears via the shift solenoid based on data from the automatic transmission’s gear speed and position via the sensor. But all this functioning is disrupted due to a faulty transmission sensor. For this, you need to check the automatic transmission sensor. If the sensor is bad, replace it with a new one.
3. Check PCM & Replace Bad PCM
The power control model is an important part of the automatic transmission system. The PCM manages all the functions of the automatic transmission. But a bad PCM is unable to manage the full functioning of the automatic transmission system.
Therefore, the PCM should also be checked and if it is bad, it can be replaced with a new one. However, this can be a matter of high cost.
4. Check & Replace Torque Converter
The torque converter is an extremely useful part in an automatic transmission. The automatic transmission of any vehicle cannot operate without a torque converter. The torque converter transfers the engine’s rotational power to the automatic transmission.
A torque converter is a mechanical device. Therefore, the torque converter should also be checked if there is a problem shifting to high gears in an automatic transmission and in the event of a torque converter failure, it should be replaced with a new one..
However, this is a high cost operation. Because the automatic transmission needs to be disassembled from the engine to replace the torque converter.
FAQ’s
Q. How do you fix an automatic transmission not shifting?
Dirty or low transmission fluid is the most common cause of problems shifting to high gears in an automatic transmission. You can fix this problem by adding or replacing the transmission fluid.
However, there could be other mechanical reasons for this problem as well. such as a bad PCM, a bad torque converter, a faulty shifting solenoid, and a faulty sensor.
Q. Which sensor controls shifting in an automatic transmission?
In an automatic transmission, the transmission range sensor controls gear shifting by sending transmission gear position and speed signals to the PCM.
Banty is the owner of Autorepairszone.com & is also a vehicle mechanic by profession. We have almost 12 years of experience in the field of automotive repair, and we strive to provide you with accurate information about vehicle malfunctions and repairs based on our experience.