Emma Davies
Updated on September 16, 2022
The transmission control module is a vital part of any vehicle that has an automatic transmission system. Whereas other vehicles would rely on mechanical or hydraulic control over a transmission system, newer vehicles will have a transmission control module (TCM) instead.
Knowing how to reprogramme a transmission control module is only necessary if it becomes faulty, but it is unlikely that it will ever need replacing.
The universal solution to reprogramming a transmission control module is to disconnect the battery terminals and let the system drain for 5-30 minutes. When you reconnect the battery, the TCM should be reset.
The module is used to communicate information to other computer systems in the vehicle and made sure your transmission is in the best gear at any time so your fuel consumption and performance are at the prime level at all times.
How Do You Reprogram a Transmission Control Module?
So how do you reprogram a transmission control module? Not everyone knows how to perform this at home without needing mechanics tools.
Reprogramming your transmission control module is useful to help reset the adaptive memory in your transmission which you can’t do whilst driving as certain things must be done whilst you are coasting to speed in neutral.
Every car is different and may require a slightly altered version of this process but we do also have articles with specific steps for a Ford or Mazda 3.
This process also involves disconnecting your vehicle’s battery which is not recommended for some models and comes with the risk of electric shock so you need to exercise caution when doing so.
You will need:
- A helper
- Multimeter
Steps:
- Before you start you need to disconnect the negative/ground cable from your battery, this means when you are working near the car’s computer you don’t need to worry about avoiding an electric shock if you accidentally touched it.
- Disconnect the positive cable from your battery and starter solenoid.
- Pull out your vehicle’s transmission control module. You may need to unplug it but it depends on its location. It should be easy to find either behind your glove box, under either of the front seats, or on the driver’s side front engine compartment edge.
- Look for a grey wire with a stripe of black/white on the harness connector of your TCM, this wire controls whether your vehicle will enter fail-safe mode when it enters into Neutral or Park (P)
- Connect your multimeter to this wire once located and ground it, then put your transmission into Park if you have an automatic or Neutral if you have a manual. If your multimeter begins reading anything lower than 11 volts then you know your vehicle can now enter fail-safe mode.
- Connect your battery cables in the reserve order that you previously carried out and leave it to run for 20 seconds before turning off your engine.
- Disconnect the battery cables again and leave them disconnected whilst you reconnect and replace the TCM. Make sure you put the signal wire connectors back to their original state.
- Once your TCM and battery are reinstalled you can start your vehicle again.
- You should now find your TCM has been reset and functioning as normal.
How to Identify a Bad Transmission Control Module
The transmission control can be located under the cover at the back of your transmission case, just below the engine’s control module. Inspecting your transmission control module is often the first way to identify if there are any faults that need repairing.
A bad transmission control module will need to be repaired immediately as it directly affects your ability to control the vehicle and maintain safe driving conditions on the roads.
Check Engine Light
The check engine light can be a warning relating to several issues in your vehicle. But if yours has illuminated and you also have one or more of the other symptoms in your car then this is a strong indicator that your transmission control module is faulty.
When you use a scan tool on your vehicle the P0700 code may appear which is a sign that your vehicle’s check engine light has illuminated to alert you of a TCM fault.
Problems Shifting
There is a large variety of shifting problems you may face when your transmission control module is faulty. This can be as simple as an annoying unintended shift or extremely dangerous such as shifting into neutral and not moving the vehicle.
Unless you have the option to manually override your automatic transmission then you won’t be able to safely drive your vehicle and should get towed to a mechanic who can replace and fix your TCM.
As you increase speed your transmission should work its way up through the gears to keep you in the right gear for the speeds you want to achieve.
The same happens when you start to decrease in speed, your transmission will start to work its way down through the gears and eventually get to first gear so you can safely take off again when you stop moving.
A bad transmission control module will not enable you to move when accelerating as it will not be able to detect the right gears for your speed which can prove highly hazardous on the roads.
Fuel Economy
Your transmission system is also responsible for maintaining the best fuel consumption levels by selecting the optimal gears and timing. If your TCM is failing then it will cause your engine greater stress and it will have to work much harder and this will lead to additional fuel consumption.
Erratic Transmission Performance
If your car’s performance is less than consistent this could be due to the transmission module not shifting correctly. It could also be due to an electric problem but this does usually end in the TCM needing to be replaced.
You may also notice problems after you have been idling or driving at low speeds for an extended period of time.If you are experiencing any of these issues they can quickly lead to serious consequences, it would be advised that you get booked in with a mechanic asap.
FAQs
Is it good to reset your transmission?
Unless your vehicle is having issues and you think it needs resetting then you do not need to reset it. Doing so will cause your vehicle to shift differently than you are familiar with.
Do you have to reprogram a transmission control module?
If you have had a transmission control module replacement performed then you will need it to be programmed so it can function properly in your vehicle.
What happens when a transmission control module goes bad?
If your TCM has started to fail you may notice issues such as:
- Bad shifting
- Slow acceleration
- Poor fuel economy
- Unpredictable gear changes
What causes TCM failure?
Your TCM will start to fail if there is a burnt circuit, faulty resistor, or a transistor on a printed circuit board. You should always get a mechanic to carry out any work on these problems.
Conclusion
A faulty TCM can cause some unpredictable shifting which can be extremely dangerous. It can also lead to poor fuel economy and slow acceleration making it less than ideal driving conditions.
If you are starting to notice some of the signs of a faulty transmission control module then you should not wait to get it seen by a mechanic.
Knowing how to reprogram a transmission control module can not only help your vehicle if there have been issues with your car, but it can also save you some money by carrying out the repairs yourself.
You may also be interested in these articles:
Where Is Transmission Control Module Located?
Where Is the Chevy Transmission Control Module? How Do You Reset It?
How to Reset a Toyota Transmission Control Module
