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:

  • Unexpected shifting.
  • Not upshift and downshift properly.
  • Gear stuck in the one mode.
  • Fuel consumes a lot.
  • CEL turns on.
  • 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!

7 Signs of a Bad Transmission Control Module

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?

  • Reset the TCM.
  • 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 the additional info about fuse location.
  • Check if it contains any burn or smokey marks. 
  • Replace the fuse with a new one. 
  • 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?

  • Turn on your vehicle engine only.
  • Shift the gear to Park mode.
  • Put the ignition key inside your truck to switch to the Run or On position.
  • Take out the override slot card (made out of plastic) from the shift lock using a plain screwdriver. Wait for a few seconds.
  • With the same tool, push it down to the shift lock. Continue pushing it for the following steps.
  • Use force using your foot on the brake pedal.
  • Change the Park mode to Neutral mode by moving the gear knob.
  • 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?

  • Locate the TCM inside the vehicle using your user manual.
  • After that, take out the 2 wires that are wired to hold the TCM.
  • Detach the nuts and bolts using a suitable tool.
  • Remove the TCM unit. 
  • Take a small brush to wipe out the dust. 
  • Use a strong penetrating oil spray like WD-40 Specialist Contact Cleaner to lubricate the unit. 
  • 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?

  • Grab an OBD II type scan tool and plug it inside your truck’s USB hub areas. 
  • Turn on your scanner tool and it’ll auto scan for fault codes. 
  • Wait for some while. 
  • 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.
  • Turn on your truck and look at the dashboard to locate the CEL sign. It won’t pop after this troubleshoot. 

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 superhot. It happens due to the suddenly lost connection that fails to send the needed signals (shift into lower gears) when speeding up on high velocities. 

How To Fix It?

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

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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