What an illuminated check transmission light means
By: Leon Rhodes
The check transmission symbol on most new vehicles has a simple gear symbol. On older vehicles the engine and transmission often share a warning light that looks like an engine.

Has the transmission warning light in your vehicle turned on and you'd like to know what it means? Are you unsure of what it means? Curious about what may have caused it? This guide explains what it means and describes common causes and symptoms to help relieve any anxiety it may have caused you.
The transmission warning light on your vehicle's dashboard is part of the onboard early warning system. An activated warning light indicates a problem with your transmission's performance or, on some models, that maintenance is required.
How a transmission light works
A sensor, often called a temperature gauge, inside your transmission monitors the temperature which, during normal use, is between 175 and 220 degrees Fahrenheit (80-105 degrees Celsius).
If the sensor detects an above normal temperature it signals the onboard computer which turns on the transmission warning light. Warning lights are designed to warn you of a potential problem with your vehicle's performance.
What causes the transmission light to turn on?
Transmission overheating can cause the warning light to turn on. Overheating, in turn, is most often caused by improper transmission fluid levels, old fluid (dark, burnt smelling), deposit buildup, a clogged filter, excessively worn parts, extreme use conditions and mechanical damage.
All of these conditions create additional friction and friction creates heat so a heat sensing warning light system is very effective at detecting a wide range of transmission issues.
Is a transmission warning light serious?
All warning lights should be taken seriously. A transmission warning light can indicate one of many different problems, some of which are simple to fix and others require a certified transmission specialist with proper diagnostic equipment to repair.
What should you do when the transmission light comes on?
Don't panic. Park the vehicle for 10-20 minutes to let it cool off and check the transmission fluid level, if possible. If it's low and you didn't detect any other symptoms, such as vibrations or hard shifting, you can usually top it off with fresh transmission fluid and see if the light persists.
Check with your owner's manual to be sure. Additionally, on some vehicles, the warning light signals a need for regular maintenance at pre-determined intervals. In all cases, the light indicates it's time to schedule an appointment for an inspection by a mechanic, dealer or transmission technician.