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Symptoms of a Bad Transmission Control Module

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Symptoms of a Bad Transmission Control Module

Various components make up a car. Such components work in tandem for smooth driving. Amongst these components is the TCM (transmission control module).

TCM is an electronic device responsible for collecting and processing signals within the car’s transmission and controlling the shifting of the transmission gear. It works closely with the parts that depend on its functionality, such as the engine, turbine sensor, and brake pedal position sensor, among others. 

Without TCM, your transmission will not be able to shift gears consistently. This might lead other components of your car to break down. 

The transmission control module functions differently- manual transmissions compared to automatic transmissions. This helps with timing gear adjustments. Therefore, TCM is entirely outdated in manual transmissions.

You’ll always have to adjust a manual car’s gears with your hands. It makes the detecting powers of your TCM completely unnecessary. Thus, if you have a manual vehicle, you do not need to worry about TCM issues. 

Identifying issues with TCM is essential to help keep your car out of car repair shops. In this post, we will discuss how to identify symptoms of a bad TCM. Read on!

Can a transmission control module be tested?

It is possible to test your TCM. However, if you do not know how to go about it, it is advisable to seek services of a professional technician or mechanic.  

Here are some ways you can test your TCM:

  • Using a scope – it involves using a pressure sensor on transmission issues and exhaust or cooling problems. A pressure sensor is amongst the common reaches you can find in car parts/repair shops. It turns air and fluid pressure abnormalities into alerts for you to take a more suitable diagnostic. 
  • Using a scanning tool – it shows you possible communication problems affecting the transmission controller and the PCM. 
  • Using a multi-meter – it reads the resistance, voltage, and frequency. It helps you check the solenoid and other parameters to know if there are issues with TCM.
  • Using a TCM software transfer tool – helps you know if you need to replace the unit.
  • Using a battery charger – helpful since you need it when installing or removing a TCM.

Mintt LogoWhere is the transmission control module located?

The transmission control module is located at the rear end of your car’s engine. It utilizes computerized technology to ascertain how and when to adjust gears for optimum driving performance. It means that moving from one gear to the other is an easy and smooth process.

Because of this, the gears will not experience much wear and tear to keep your transmission in a healthy state for a longer time. Thus, your vehicle will experience challenges when adjusting to different gears if it does not have TCM. 

Besides helping in adjusting gears for better driving performance, the transmission control module has other duties. These include:

  • It stores information about your car’s transmission. This information is used later in gear shifting depending on the driving situations.
  • It receives signals from the sensors and transmits them to lock up the clutch. In doing so, it helps in managing power and fuel-efficiency. 

How do I know if my transmission is failing? 

Identifying issues with your TCM is crucial in stopping further damage to various essential components of your car. Fortunately, symptoms of a bad TCM are easy to recognize. The most common symptoms of a bad or failing TCM include:


  • Poor fuel economy


Both the transmission control module and engine work together for optimum fuel economy. Therefore, a faulty transmission control module causes poor fuel economy. The TCM malfunction in adjusting the gears, which in turn, hurts your gas mileage. 


  • Check engine light 


The illumination of the check engine light on the dashboard can be a sign of many things. However, any issue with your shifting as well as the check engine light illuminating indicate issues with your TCM. Besides, it might indicate problems with other parts of the transmission systems. 


  • Trouble shifting into higher gears 


Usually, your transmission should smoothly shift into higher gears as you slowly increase speed. If this does not happen, the engine’s RMP will keep increasing instead of decreasing. Since each gear has a maximum speed, you might not reach an intended speed if a bad TCM can’t shift to higher gears. 


  • Delayed shifting 


It is amongst the common faulty transmission control module symptoms. It happens when you attempt to go faster but unable to do so. Then after some seconds, your vehicle adjusts the gear and accelerate.  


  • Stuck in gear 


It usually occurs when you are stuck in neutral or first gear; you are unable to shift from one gear to the other. If this happens, you’ll remain stagnant when in neutral, and you’ll be driving at a limited speed when stuck in the first gear. 


  • Random shifting of gears 


When your transmission starts picking gears randomly, then there is a problem with your TCM. The gear shifts do not match your speed or keep shifting into neutral. In such a situation, seek the right service right away.


The TCM can run for a long time without experiencing significant issues. However, excess heat from your engine, as well as constant use, can undesirably affect its efficiency.

Luckily, the above signs will help you identify if you have a faulty TCM. If you are unable to solve the problem, you should seek assistance from a technician. But if it is damaged, have your TCM module replaced. 


Comment (1)

  • Catherine Reply

    Can a bad TCM computer cause the vehicle showing 300 degrees but not hot at all? The dealer had me replace Transmission Solenoid, Sump Filter and cooler return filter. Now says the rebuilt TCM is bad and sending it back to be rebuilt. Why would this hot 300 degrees be a bad read out from the computer?

    September 13, 2021 at 2:00 pm

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