What Does the Check Transmission Light Mean?

by Thomas WestUpdated July 07, 2023

Many functions in your vehicle are controlled by the main engine computer, including how and when the transmission shifts gears. To get optimum fuel mileage and performance from your vehicle, computer-controlled shifts are the norm in most modern cars and trucks.

In older vehicles, you may not have realized you had a transmission problem until you found yourself stranded. Most new vehicles have a warning light that lets you know of transmission problems before they become a major expense.

Warning Light - Check Engine Light

While some vehicles may have an actual check transmission warning light, other cars and trucks may inform you of impending transmission problems by using an existing warning light -- such as the overdrive, service or traction control lights.

Read your vehicle owner’s manual to determine how the main engine computer informs you of a transmission problem. Some lights may stay on or may flash on and off until the problem is fixed.

Fault or Reminder

A transmission warning light may serve a double duty. It may inform you of transmission faults, but the transmission light in some vehicles may also serve as a maintenance reminder to let you know it is time to check or change your transmission fluid, or to take your vehicle to the dealer for regular maintenance.

For instance, if your transmission warning light came on just after the vehicle turned over 100,000 miles and you do not feel there is any problem with the transmission, the light may be just a reminder to perform scheduled maintenance. Check your owner’s manual or call the dealer to be sure.

If it’s not a scheduled maintenance, it could be any number of other things, including having low transmission fluid, fluid leaks, transmission issues, overheating, or other transmission damage.

There are different trouble codes for different internal components of the vehicle’s transmission, and sometimes it’s necessary for a professional mechanic to take a look to tell you exactly what the transmission light means. The difference between having a low transmission fluid level or a transmission fluid leak or the transmission overheating can really change how to fix the transmission system.

Checking the Fluid

One of the first things you should do if your transmission warning light comes on is to check the transmission fluid, if possible.

  • Some vehicles have a sealed transmission that cannot be checked by the owner, especially automatic transmissions, but some have a dipstick -- much like the one used to check engine oil level -- so that you can check the transmission fluid level when required.
  • Usually older vehicles and manual transmissions have the ability to check the transmission control module.
  • Some vehicles require that the vehicle be warmed up and running while checking the fluid, but check the owner’s manual for the correct procedure first. If the fluid is low, add only fluid that is specified by the manufacturer to avoid further transmission problems.

If the warning light is still on after adding fluid and driving a few miles, there may be another problem.

Symptoms of Trouble

The conditions under which your car’s transmission warning light comes on may help to point you to the problem area quicker.

  • A problem with a transmission temperature sender may be the culprit if the light comes on or flashes only before the vehicle has warmed up to operating temperature.
  • A light that flickers or comes on only when hitting bumps on the roadway may indicate a loose transmission wiring connection or a bare wire.
  • Other problems, such as harsh or erratic shifting, not shifting from first gear automatically or transmission fluid that appears dark or smells burnt are problems that do not require a transmission warning light to tell you that there is a problem.

Your dealer or a transmission repair garage can scan the main engine computer to obtain transmission fault codes. The fault codes may point to a problem -- such as a bad shift solenoid -- that may not require a complete transmission rebuilt, thus saving you some money.

The bottom line if to check transmission lights often and to be aware of the common causes of an illuminated transmission light. Just like you might associate a burning smell with internal transmission failure, you can be aware of other auto repair issues like issues with the powertrain or torque converter and know the answers to common FAQs next time you see your transmission light on.

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