6 Signs Of A Bad Transmission Control Module!

Being a crucial electronic part, the TCM (Transmission Control Module) controls and maintains the transmission gear shifting smoothly by passing the signals. 

Sometimes this small part fails to work by catching errors and showing early signs to get proper attention. Here are the common symptoms:

  1. Unexpected shifting.
  2. Not upshift and downshift properly.
  3. Gear stuck in the one mode.
  4. Fuel consumes a lot.
  5. CEL turns on.
  6. The transmission gets overheated.

After seeing the preview of 6 signs of a bad transmission control module, it’s time to find out the root reason why these happen and ways to fix them. Let’s go!

How Does a Transmission Control Module Work?

Before we talk about the signs of a bad TCM and how you can fix the issues, here are a few words about how a TCM works.

Simply put, the TCM tells your vehicle the right time to change gears. It’s like a tiny computer and it receives information from different sensors so it can keep the transmission updated and working properly.

Some of the sensors are the fluid temperature sensor, turbine speed sensor, and throttle sensor. All of the sensors provide information regarding vehicle performance and driving conditions so the TCM can change gears accordingly.

Similarly, the wheel speed sensors send information to the Transmission Control Module and the data helps to determine when the transmission decouples. It eventually helps you determine when to push the clutch on a manual transmission car.

Signs Of A Bad Transmission Control Module & Its Solutions!

In order to treat the issue, you’ll need to learn about the symptoms of a bad transmission module. Now, I’m about to mention all signs in detail with a proper reason and their fixes. 

1. Unexpected Shifting.

Instead of acting rightly, the sudden shifting of gear can cause accidents in different terrain. The unintended shift happens when the TCM is facing some issues and fails to read the real condition of the gear.

How To Fix It?

  • Open the hood and locate the TCM unit based on your truck model. 
  • Remove the part after disconnecting the wires and nuts. 
  • Insert new TCM which is OE standard like the ACDelco GM Genuine Parts 24256864.
  • Attach everything back to its place.

2. Not Upshifting & Downshifting Properly.

To go down the hilly or down areas, it’s essential to change into a lower or higher gear. And when the TCM goes bad, it stops sending signals causing it not to upshift or downshift. The real culprit is the blown transmission control module fuse.

How To Fix It?

  1. Reset the TCM.
  2. If that doesn’t work, locate the TCM fuse in the main fuse block. It mostly contains a 10-amp label in the fuse. Check your user manual to find additional info about the fuse location.
  3. Check if it contains any burn or smokey marks. 
  4. Replace the fuse with a new one. 
  5. Then, check if the truck upshifts and downshifts properly or not.

3. Gear Stuck In The One Mode.

Not changing to other gears or stuck in two or one mode is what a faulty TCM causes. Most of the time, the gear stuck to Park (P) or Neutral (N) and refuse to change into other gears. Sometimes it happens due to the lime mode to ensure the safety of the truck.

How To Fix It?

  1. Turn on your vehicle engine only.
  2. Shift the gear to Park mode.
  3. Put the ignition key inside your truck to switch to the Run or On position.
  4. Take out the override slot card (made out of plastic) from the shift lock using a plain screwdriver. Wait for a few seconds.
  5. With the same tool, push it down to the shift lock. Continue pushing it for the following steps.
  6. Use force using your foot on the brake pedal.
  7. Change the Park mode to Neutral mode by moving the gear knob.
  8. Start your truck to see if the gear shifts naturally or not.

4. Fuel Consumes A Lot.

As the bad TCM unit tends to stop the working of the gear shift when speeding up, the truck run at high speed. And so, it eventually spends fuel more and more. Sometimes an unclean TCM unit causes this kind of sign.

How To Fix It?

  1. Locate the TCM inside the vehicle using your user manual.
  2. After that, take out the 2 wires that are wired to hold the TCM.
  3. Detach the nuts and bolts using a suitable tool.
  4. Remove the TCM unit. 
  5. Take a small brush to wipe out the dust. 
  6. Use a strong penetrating oil spray like WD-40 Specialist Contact Cleaner to lubricate the unit. 
  7. Attach everything back to its place after 20 minutes. 

5. CEL Turns On.

The CEL (Check Engine Light) turning on is a serious sign that mostly happens due to TCM error. You’ll notice a yellow CEL light popping in the dash which indicates the issue with one or more fault codes on the TCM unit.

How To Fix It?

  1. Grab an OBD II-type scan tool and plug it inside your truck’s USB hub areas. 
  2. Turn on your scanner tool and it’ll auto-scan for fault codes. 
  3. Wait for some while. 
  4. If you see any fault codes like U0101 (lost connection of TCM) or P0613 (error on TCM unit), then clear the codes to fix the TCM error.
  5. Turn on your truck and look at the dashboard to locate the CEL sign. It won’t pop after this troubleshooting. 

6. Transmission Gets Overheated.

Apart from an improper oil change and weight increase, the faulty TCM is another reason why the transmission tends to get super hot. It happens due to the suddenly lost connection that fails to send the needed signals (shift into lower gears) when speeding up at high velocities. 

How To Fix It?

  1. Open the hood of your truck.
  2. Locate the battery.
  3. Take out the negative terminal from the negative side of the battery.
  4. Then, disconnect the positive terminal from the positive side of the battery.
  5. Let it sit like this for 5 – 30 minutes.
  6. Connect the negative and then positive terminals on the battery. That’s how the transmission control module reset.

Why Does A Transmission Control Module Fail?

Since the TCM works like the brain of your vehicle, it needs to work properly. Once the previously-mentioned sensors malfunction, it provides wrong information to the TCM. And, without the correct data, the TCM can’t make necessary adjustments and you can’t get a smooth ride.

Below are some reasons why a TCM can fail.

Heat from The Engine

Since the TCM is nothing but a set of electronic parts, it’s more likely to damage from heat. The plastic and metallic encasing of the TCM protects it against heat. But sometimes, the parts can fail to give enough protection and get damaged by extreme heat.


Cars tend to vibrate now and then because the engine itself creates vibration. The vibration can increase according to the increase of the RPMs and speed.

Driving on too bumpy roads can cause your car to vibrate. And, unusual vibration isn’t good for the TCM.

Wear and Tear

It’s natural that the TCM will gradually wear and tear over time because of use and age. Factors like road conditions, weather, lack of maintenance, and corrosive substances can speed up the wear and tear process.

Incorrect Soldering in TCM Circuit Board

Another reason why the TCM can prematurely fail is bad soldering in the circuit board. If this happens to you when your vehicle is still under warranty, you can consult the manufacturer and claim the pay for fixing the issue.

Transmission Control Module Repair and Replacement Costs

The overall replacement cost will be anywhere from $500 to $1,500 depending on the make and model of your vehicle. Both the cost of the parts and the labor cost can vary widely based on where you live and what type of vehicle you own.

For example, the TCM in some vehicles is positioned inside the transmission, and opening the transmission is hard. In such cases, labor costs can be around $300.

On the other hand, the TCM is positioned somewhere more reachable. So, the replacement process will not be more than just pulling one part out and plugging the new one in. In such cases, labor costs will be less.

And, the price of the TCM parts can highly vary based on the models of your vehicle. For example, the parts of a TCM for a Honda CR-V are around $360 whereas it’s $1,240 for a Volvo S-80.

And, if your TCM doesn’t need a replacement but a repair, minus the cost of the parts. You only need to pay the labor expenditure in that case which varies from different area.

Can You Replace A Bad TCM Yourself?

Of course, it’s a great idea to replace it on your own because you can save a few hundred dollars by doing so. But whether you can replace the TCM on your own depends on where the TCM is located in your vehicle. 

We’ve mentioned two different cases about the location of the TCM. If it’s easily reachable, you can take the risk. Otherwise, it’s best to get it replaced by an efficient mechanic to prevent any further damage.

About what you need, you can remove the TCM only using your hands if it’s easy to reach. Otherwise, you may need things like a socket wrench, a screwdriver, and a towel to clean any debris.

Below is the process of replacing a TCM. Put your DIY hat on and get started!

  • Purchase the right TCM: You can’t make a mistake in this step. It’s a must to buy the correct TCM for the year, model, and make of your vehicle. For example, if it’s for a 2017 Honda Accord, don’t buy a TCM that’s designed for a 2009 Chevy Silverado.
  • Locate the TCM: Although the location of the TCM varies in different vehicles, check near the transmission area in the first place. It’s because, in most vehicles, this is the commonplace for a TCM to be. You’ll notice a wiring attached to the data port of the TCM that makes the connection to the engine control module.

If you can’t locate the TCM, check the owner’s manual and try to find it out. If you can’t get it yet, consult a mechanic and let him handle things.

  • Take off the old TCM: Unscrew the screws and bolts that attach the TCM in place. In some vehicles, it just takes lifting the plastic tab holding the TCM in place. Take off the wire that’s attached to the data port of the TCM.

Keep the screws and bolts near you because losing them will make installing the new TCM harder.

  • Install the new TCM: Installing the new TCM is nothing but the opposite process of removing it. Take the screws and bolts you kept near and use them to set the new TCM in place. Make sure the screws and bolts are tight enough.

Yes, that’s all.

Signs Of A Bad Transmission Control Module Infographic

Ending Note

Tracking all the early signs of a bad transmission control module will help you to understand if the TCM needs fixing or not.

Now, as you have proper knowledge about this topic, check the behaviors of your truck to detect if it is showing similar symptoms.

If your truck seems to act the same way, I’ve given step-by-step solutions above so you can freely try them. Plus, grab some handy tools to try DIY repair. Hope this guide helps to get the in-depth details that you needed. Thank You For Reading This Guide!

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at Autoglobes.com with a passion for the automotive industry.