How To Test TCM Duramax: In 7 Useful Steps

Imagine you are on a long drive through a beautiful bridge. Suddenly while moving down from the bridge, your gear shifts itself, and your vehicle becomes numb! Your tries fail to change the gear! 

Fuel ran out too! To make the situation worse, the check engine light is also smiling at you being shone! Being unable to accelerate the vehicle, you are now a helpless man alone on the bridge slope! You must not want this situation. 

But if you are unfortunately in, then what to do? The first thing you should do then is to test the TCM. For doing this test, you have to know that how to test tcm Duramax. If you cannot do it yourself, you would better call a mechanic and wait till he comes.

In this guide, we’ll help you learn how to test your TCM Duramax yourself so that you don’t be helpless with your vehicle in any urgent situation.

How To Test TCM Duramax

Things Required To Test TCM Duramax:

Before starting to test the TCM, you need to be appropriately equipped. The cost of testing and the time required is also to assume. 

Then you’ll start the testing step by step. We will help you here with all the necessary information you need now.

Estimated cost:

If you are well equipped and know how to test tcm Duramax, it will cost nothing. If you have to call a mechanic to test that, then some costs may be estimated. Otherwise, the estimated cost is zero.

Time needed:

The TCM testing is not that time-consuming. But if you are a newbie, you may need about 20 to 30 minutes most.


The tools you need for the testing procedure are-

  • Screwdriver 
  • Pushpin clip removal tool
  • Multimeter
  • Scanning tool
  • Scope

If you need to remove and replace the TCM, then you need-

  • A new TCM
  • Battery charger
  • Your safety equipment (glasses and gloves etc.)
  • TCM software transfer tool


You don’t need to have any specific materials for tcm testing. But enough fuel or an extra fuel container should be kept ready always.

How To Test TCM Duramax – 7 Useful Steps

To test the TCM on your vehicle, you need to follow some steps-

Step 1 – Covering TCM Beside The Fan Cover

Open the shield covering the TCM beside the fan cover. You can use a screwdriver and other opening tools here.

Step 2 – Remove the connector

Remove the connector. Push down the button-like socket. The lock will be opened.

Step 3 – Push The Side Pins

Push the side pins up. The factory TCM will come out on your hand.

Step 4 – Check Pins And Ports

Manually test the TCM. Check its pins and ports. If anything there is loose or broken, you have already found a problem. If not, then carry on for the next steps.

Step 5 – Connect Multimeter With TCM

Connect a multimeter with the TCM. Measure the frequency, voltage, etc. Check data to understand the condition of your TCM.

Step 6 – Use A Scanning Tool

Use a scanning tool to check that if the communication problem was disturbing the transmission controller and PCM. 

Step 7 – If There Still Problems, Change The TCM

Problems with fluid or air pressure, an anomaly in cooling, or exhaustion can be read with a scope more perfectly. This tool will alert you with an alarm if any problem is found.

Your testing procedure is finished now. If you have found problems with your TCM through these steps, you should change the TCM as soon as possible. Before changing it, learn more clearly about the process.

You can see the youtube videos about it to get a clearer view. Videos from ‘South main auto repair LLC,’ Spartan Autoworx, etc., will possibly be helpful.

If no anomaly is found, check the other parts of your vehicle or call an expert mechanic.

Frequently Asked Questions

How can I know that my TCM is bad?

You should know that your TCM Duramax is bad if-

  • Your vehicle cannot speed up as usual.
  • Gear often freezes.
  • You cannot shift the gears urgently.
  • Gear slips a lot.
  • Your vehicle needs more fuels nowadays.
  • The engine is overheated soon after starting to drive.
  • You get your check engine light on.

So, if you are in with these symptoms, immediately think about how to test tcm Duramax.

Does a Duramax TCM have to be programmed?

Yes, it has to be programmed. If you have just got a Duramax truck and your transmission is brand new, then the TCM will need to be reprogrammed. 

If it has had transmission problems in the past, then you will need to have the TCM replaced with a new one.

Will a bad TCM throw a code?

A bad TCM throws mainly the p codes while the check engine light is on. These codes are usually-

  • P0612
  • P0613
  • P0700
  • P0706

Can I drive with a bad TCM?

Driving with a bad TCM is tough. Problems like automatic gear reduction, gear stiffness while trying to change, bad fuel economy, illuminated check-engine light, poor acceleration can interrupt your drive with a bad TCM. Thus the chance of accidents or sudden stopping is much more.

So, probably you can, but you shouldn’t drive with a bad TCM. 

How can I reset my TCM Duramax?

To reset your TCM Duramax, you have to go through some steps. The steps are-

  • Turn the key position to ‘2’. Keep the engine off. Try listening to the two clickings and make sure the dash lights are on.
  • Press the gas pedal down and ignite the kick-down switch. Don’t stop your pushdown process.
  • Keep pushing and wait for at least 10 to 12 minutes.
  • Turn the key to zero keeping the pedal pressed. You do not need to remove the key from the hole.
  • Release the gas pedal now.
  • Wait for 2-3 minutes to give the engine some rest.
  • Now, you can go for a drive.

Can I run biodiesel in my Duramax?

Yes, you can. It is recommended that if you run it in your fuel system, the truck has all of the upgrades. Such as a fuel filter and a good FICM to handle the extra load.

What causes a Duramax to go into limp mode?

A Duramax goes into limp mode whenever the EPC light comes on. This is triggered by a problem with the microprocessors in the engine control system. 

The light should be turned off after about 1 hour, but if it doesn’t, then you will need to have the EPC replaced.

Final Words

Finally, it is good to learn that how to test tcm Duramax. But better is to call a more experienced mechanic equipped and have more expertise than you because you must not want your vehicle to be fatal or spoiled at all!

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