Bad Transmission Control Module (TCM) Symptoms and Replacement Cost

bad transmission control module symptoms

An important part of a vehicle’s automatic transmission system is the transmission control module ( TCM ). Compared to traditional mechanical or hydraulic transmission control, updated vehicles use a transmission control module. Usually, this component does not require any replacement, but at the first sign of bad transmission control module symptoms, you must have your car checked by a professional technician as soon as possible.

The transmission control module automates gear selection. This is one of the reasons why most modern cars have enhanced driving performance and are fuel-efficient. This component is located below the back of the transmission cover and underneath the engine control. In some car models, this is located at the bottom of the central control system or right beside the battery.


Bad transmission control module symptoms

Take note that any problems with the transmission control module must be checked by a technician as soon as possible. Driving with bad TCM symptoms can be very dangerous as you can lose control of your vehicle as you’re driving it. Beware of the following symptoms:

1. Blinking check engine light

If you see your check engine light flickering or you see the warning light on the dashboard, this could be due to a variety of problems. However, if the check engine light is on as you experience shifting problems, then this could be due to problems with the TCM or other components of the car’s transmission.

To confirm if your car has bad TCM, a technician will use an electronic diagnostic tool to check your engine. A code P0700 means that your vehicle has problems with the TCM.

2. Uncontrollable shifting

In a modern vehicle, the automatic transmission needs the help of the TCM to shift properly. Therefore, any problems with this component will lead to uncontrollable or incorrect shifting. Usually, this symptom starts as an annoying thing, but when this is overlooked, you and your passengers may suffer from an accident.

If you suddenly experience this problem and if you have a manual override, then you can still control your vehicle until you get to a car repair shop to have the transmission control module checked.

3. Problems with shifting

As a car increases speed, the transmission corrects shifting to higher gears in time. But if this does not happen, the engine's speed may continually increase rather than dropping during the upshift. Every gear has a maximum speed, but you may not reach this speed if the broken TCM does not increase gears.

A car with a bad TCM will also encounter problems with downshifting. This is like the previous symptom, but only in reverse. You'll find this annoying if you want to pass a slow vehicle. Also, if you're coming to a stoplight, an intersection, or a pedestrian, and you cannot properly shift gears, you’ll remain in high gear. And when it’s time to move again, you are in very high gear to accelerate properly, and this can prevent your movement.

4. You can’t shift gears

A broken TCM may prevent you from moving into higher or lower gears, and you’ll be stuck in neutral. You won’t be able to shift or go anywhere as you’ll be stuck in first gear speeds.

5. Delays in shifting

A bad TCM may affect your acceleration, which will make you lose speeds than increase your speeds. As you are near a hill, you won’t be able to shift at all. And if you want to pass a slow-moving car while driving on a two-lane, your car may refuse to downshift quickly to have enough torque to pass.

6. Your car is using more fuel than usual

Any problems with a car’s transmission system will result in poor fuel economy because this component is needed for ideal gear selection and proper gear timing for proper fuel economy. You will end up spending more money on fuel in the long run. To save on fuel and to optimize your vehicle’s performance, you must have a poorly-functioning TCM checked right away.

Transmission control module replacement cost

If you’re asking how much does it cost to fix a transmission control module, it may cost around $500 up to $900. Expect the TCM component to cost from $450 up to $700, and labor may be from $50 up to $200.

Some car owners reduce parts replacement costs or transmission control module replacement costs by buying parts online. Once the new part arrives, you may simply contact a mechanic to have it replaced. You will be charged an hourly rate. This rate varies from one mechanic to another. Also, expect taxes and additional fees to be included in your total bill.

Can a broken TCM be repaired? In some cases or depending on how broken the component is, you can expect to save money instead of buying a brand new one. Repairs may cost only $300, which is just a fraction of the cost of a new TCM. Repair costs may also vary depending on the location. Repair centers located in urban areas may charge more than those located in rural areas.

Most TCM repairs are covered with a warranty; however, some car owners prefer to pay more with a new TCM rather than using an old one. There’s still a risk of problems with an old TCM, which may arise if the repair is done haphazardly.

In most cases, a broken TCM will be taken to a specialized repair center. You may need to wait for many weeks or months before this can get fixed. You may be left without a car to use as well. These are practical reasons for replacing a broken module with a new one. 

Final Words

Bad transmission control module symptoms usually arise from electrical problems, corrosion build up on the component, and damage due to stress. It's important to have your vehicle checked right away at the first sign of a bad module problem. Finally, rely only on the certified technicians for


About the Author JamesL Davis

James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.

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