Signs of a bad transmission control module and the cost of replacement

Automatic transmission systems are different from their manual counterparts. Automatic transmission systems are more advanced and rely on computerized systems for their operation. Automatic transmission systems use a transmission control module (TCM) to select gears, optimize performance and control fuel efficiency. Driving around with a bad transmission control module is risky in many ways. Drivers must identify early signs of failure or defects affecting the performance of transmission control modules for timely repair or replacement before the car is grounded.

Here are the common symptoms of a bad TCM. Finally, we break down the cost of replacing or repairing damaged transmission control modules.

Check engine light comes on

The use of advanced sensors allows drivers to monitor their vehicles in real-time. Several defects can cause the check engine light to come on. However, if the light comes on and the driver experiences difficulty when shifting, there is an issue with the transmission control module. A scan is necessary for the driver to pinpoint the source of the error. If the scan tool returns the P0700 code, you should have the TCM checked.

Bad shifting

A faulty TCM misinterprets computer signals. The car shifts into the wrong gears. In some instances, the gears change without human intervention and warning. Bad shifting is a safety risk. Once you experience this, take the car for repair.

Difficulty shifting to higher gears

The TCM controls the timing for shifting to higher gears. When the TCM is bad, engine RPM increases instead of dropping. In extreme situations, the transmission fails to change to high gear.

Problematic downshifting

When decelerating, the TCM should automatically downshift the gears. When the foot is released from the gas pedal, the transmission moves to a lower gear to optimize fuel efficiency. If the transmission control module is faulty, it becomes hard for the vehicle to downshift. 

The transmission is stuck in a single gear

A bad TCM causes the vehicle to get stuck in one engine. It is common for transmission to get stuck in a low gear (first gear) or neutral. The driver moves around at a limited speed or can’t drive the vehicle from rest.

Delayed shifting

The transmission control module controls the intervals at which the gears shift. The time for shifting from lower to higher gears and vice versa remains constant. However, if the TCM is damaged, there will be delays when changing the gears.

Low fuel economy

The TCM is essential for timing gear changes and optimizing fuel efficiency, depending on the driving speed. A faulty TCM causes a mismatch between the gear ratios and fuel consumption. Poor fuel economy can indicate that the transmission control module is bad.

Cost of replacing the bad transmission control module

A new TCM costs between $450 and $700. Labor costs average $50-$200. Therefore, drivers spend an average of $500 to $900.


A bad transmission control module causes multiple problems that affect engine performance and driving quality. Transmission-related failures are a safety risk. When drivers identify signs of TCM failure, they should visit a repair shop for further troubleshooting and immediate replacement of the damaged transmission control modules.