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How Do I Know If My Transmission Control Module Is Bad?

How do I know if my transmission control module is bad

Your transmission control module is a key part of your vehicle. As you might expect, along with the engine and the transmission in your car, the transmission control module is a crucial component that works alongside these two huge parts, helping you and your passengers drive safely and keep the performance at a high level. When you are driving your car forward, the transmission control module is in charge of locating and analyzing the right time and place to change the current gear to make sure that the driver’s experience can be smooth and performance-oriented.

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What is the function of the transmission control module 

Aside from the main responsibility of the transmission control module, this control module can also send certain OBD-II codes that show your car’s problems to the computer in your vehicle. If your car happens to detect any malfunction or issues within the transmission, the transmission control module can send the codes. If you are wondering how you know if the transmission control module is bad, then your OBD-II codes will not be detected. These codes can appear in various forms, like the check engine light coming on and being illuminated on your dashboard, or other signs that alert you that something will not be right under the hood of your car and in your engine system.

Why the transmission control module is important 


Since the transmission control module provides a huge link between your transmission and your engine, the transmission control module is a huge part of your driving experience and performance. Without a transmission control module that works properly, your car cannot change the necessary gears when needed to drive correctly, and can lead to serious mechanical issues with your engine and transmission that require replacements and very expensive repairs. 


These parts are also in charge to improve the quality of smooth shifting in your car and the performance of your transmission system. This means that shifting between gears is smooth, easy for the driver, and does not place any extra stress on the gears. This can lead to your car not experiencing as much wear and tear on the gears, and less break down over time. This keeps your transmission in a better shape for a longer period of time, and requires fewer repairs on your transmission. 


In addition, the party's ability to send OBD-II codes to the car’s internal computer, like the electronic control module, serves as a good way to identify any potential transmission problems before something goes wrong in your vehicle and damages your engine further. This can help prevent serious damage that is expensive and requires engine replacement that is very costly and time-intensive. 

Signs of a Failing Transmission Control Module


Now that we know that the transmission control module is a huge component of a vehicle with an automatic transmission system, it is imperative to know the signs and symptoms of a failing or damaged transmission control module. Although your car’s transmission control module should technically never need replacing, if you have a damaged control module, repairs or replacements will be necessary. This module is key for communicating information with other systems in your car. 


The transmission control module can often be found below the cover at the back of the transmission and should be located just near the engine control module’s position. The position of the transmission control module is found under the center console in the interior or under the hood near the car battery. If you have a problem with this control module, you should have it looked at by a mechanic right away so that you can prevent any further damage to your car’s battery and transmission. As a driver, pay attention to the following signs and symptoms of a bad transmission control module. 

Check Engine Light


Although your check engine light can turn on for various reasons, if the check engine light illuminates on your dashboard, it can mean several things for your car, including a failing transmission control module. If you have any problems with the shifting and your shifting is rough in addition to the light showing up on your dash, then it is most likely an issue with your transmission. 


Along with the transmission control module being a problem, the check engine light can come on due to a poor fuel economy, oxygen sensor failing, mass air flow sensor failing, a loose fuel cap, catalytic converter failure, spark plug and ignition coil issues, bad spark plug wires, issues with an aftermarket alarm, and a vacuum leak. 

Unpredictable Shifting


Along with the check engine light coming on in your vehicle, there can be unpredictable and erratic shifting in your car if you have a problem with the transmission control module. Since the automatic transmission relies on the transmission control module to shift properly, a bad transmission control module can cause incorrect and unintended shifting. Unless you have a manual override option in your car, you will need to go to a mechanic or an auto body shop to have the transmission control module replaced and fix your car before it hurts your engine. 

Problems Shifting into Higher Gears


When you gradually increase the speed of your car, you should notice that your transmission should correctly move into higher gears at the right time so that you can easily drive your car uphill or while accelerating. If this does not happen in your vehicle, you will notice that your car’s engine’s RPM will keep increasing instead of slightly changing during an upshift. Since each gear has a max speed that it can hit within the gear, you might never reach the speed necessary, like if you are driving on a highway, if your car will not shift into a higher gear and allow you to drive faster. 

Problems Downshifting


This problem is similar when the car has issues shifting into higher gears, but the problem is actually in a reverse order. In order to pas a slow moving vehicle and to shit your transmission, your car will fail to go into lower gear when you press the pedal to the floor and try to quickly accelerate, whether it be passed a car or up a hill. If you are cruising down the highway at high speeds, then your transmission should be going into lower speeds when you try to slow down – like when your car comes to a stop, the automatic transmission should be changed into first gear. 


If your transmission control module is bad, then you might still be in high gear as you are going to a stop. This is a way you can tell if your control module is bad, if your car is still in a high gear when you try to slow down. 

Stuck in the Same Gear


If your car is unable to shift out of first gear and you know that your transmission control module is bad, your car will be stuck in neutral or first gear. This means that the transmission will not shift and you will not be able to move the car anywhere. 

Delayed Shifting


In order to be able to change gears and speeds of your car, your transmission control module has to cycle through various gears at the time it is necessary. If you have a bad transmission control module, then this can cause the cycle between gear to move too slowly. This can cause poor acceleration, and cause the performance of the engine to be suboptimal. When you approach a hill or you have to pull heavy loads, the shifting performance can get even worse, showing you how you know your transmission control module is bad.

Poor Fuel Economy


If you experience problems with your transmission system and your transmission control module, then this can result in a poor fuel economy and a poor fuel mileage. An automatic transmission is designated for quick and smooth gear selection and the timing, being able to  provide you with the best possible fuel economy and the most efficient gas mileage. 


If you have a transmission control module that has gone bad or is damaged, then this can aff3ect the timing and your eigen wil have to overheat and work harder than usual to give the same amount of performance. This can cause you to spend more fuel than usual, more money filling your tank, and let you know how you know your transmission control module is bad. 

Bad Transmission Control Module Replacement Cost


In order to replace the transmission control module if it is not working correctly or has been damaged over time, the replacement cost of a transmission control module ranges anywhere from $500 to $900. To determine how you know your transmission control module is bad, you will need to repair or replace the module. The parts costs are going to be around $450 to $700, while the labor costs will be between $50 and $200 in total. 

Bad Transmission Control Module Repair Cost


Sometimes, the damage is not high enough to warrant a full replacement for the transmission control module and you will just need to do the repair. Another option is to repair your TCM, with the transmission control module repair cost will be lower than replacing the module. On average, you can expect to pay around $300 to repair your transmission control module. While most TCM repair businesses will offer a warranty, it can be a real problem if the repair is not done right, since you will have to then pay for the replacement. 

Repairs related to transmission control module replacement


Along with the replacement of the transmission control module if your TCM has gone bad, there are some other repairs that are directly related to this issue. The air conditioning refrigerant line replacement runs between $561 and $591, and the alternator replacement runs between $572 and $760. 


In addition, the horn replacement and suspension shock or strut replacement are commonly associated with the bad transmission control module, and cost between $140 and $158 and $765 and $873 respectively. Furthermore, the trunk lock cylinder might also have to be replaced, running between $151 and $162. 


The last three repairs for the car that are related to the transmission control module replacement are the camshaft seal replacement for between $368 and $477, the variable valve timing actuator replacement for around $806 and $967, and the sliding door lock actuator replacement between $260 and $283. 

Can I drive with a bad transmission control module?


Now that you know the prices you will need to pay for either the repair or replacement of the transmission control module in your vehicle, it is imperative for you to know if you can drive your car safely with a bad transmission control module. 


If the transmission control module fails and has become damaged over time, it is likely to leave the car unable to drive, disabled, or only being able to function in just one or two gears, providing not the performance needed to drive your vehicle safely. This can cause the car to go into “limp mode,” where the vehicle will be unable to drive until the bad transmission control module is repaired or replaced. 


Limp mode in your car is a security feature in most modern vehicles where the computer activates the engine or transmission control unit to pick up a fault. Once the transmission control unit has picked up a problem in the vehicle, the limp mode will cause certain parts of the car that are not very important, like the air conditioning and electronics, to switch off, and reduce the speed of the car. 


Limp mode in your car can be a direct sign of a bad malfunctioning transmission control module. Some symptoms of the limp mode and the check engine light are directly related to problems with the transmission wiring, while the REV limit being between 2500-4500 RPM being the result of a malfunctioning engine boost control.


In addition, other symptoms of the limp mode include under-boost and low performance, which are related to defective engine components and the engine sensor s being faulty. The last two symptoms are restricted functions, which are caused by problems with the brake system wiring, and the transmission shifting maximum into third gear, which is due to faulty engine wiring. 


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