Like most drivers, you’re probably familiar with the check engine light. But what you might not realize is that some vehicles also have a transmission warning light that illuminates to indicate a problem with the transmission.
Because the transmission is one of the most expensive parts of your vehicle, if the warning light turns on, you’ll want to address the problem right away.
What Does the Transmission Light Look Like?
Not all vehicles have a transmission warning light. But for those that do, exactly what the light looks like will depend on the year make, and model of the vehicle.
Some cars may warn of a transmission fault by flashing the overdrive light or displaying a string of text in the driver’s information center. Others will display a symbol depicting a gear with an exclamation mark or a thermometer (for transmission over temperature) inside.
Whenever a warning light appears on your car’s dashboard, it’s a good idea to consult your owner’s manual to get an idea of what the light might mean.
Why is My Transmission Light On?
The transmission warning light (or message) indicates there’s a problem with your car’s automatic transmission or associated components. These days, automatic transmissions may have a traditional, continuously variable, or dual-clutch design.
Some vehicles only turn on the transmission warning light when the transmission is perceived to be overheating. Other cars use the light as a general warning that can indicate a broad range of transmission-related problems.
The check engine light will often turn on alongside the transmission warning light. Also, the vehicle may be forced into a fail-safe or “limp” mode when the transmission light turns on.
7 Common Causes of an Illuminated Transmission Warning Light
Unfortunately, there isn’t a one-size-fits-all answer to why the transmission warning light might be on. Some of the most common causes for the light include:
Transmission overheating is the most common cause of an illuminated transmission light. The root cause of the overheat condition could be anything from an obstructed transmission cooler to an internal transmission problem. Certain driving habits, such as towing a load that’s too heavy for your vehicle, could also cause the transmission to overheat.
Low Transmission Fluid Level
A low fluid level can cause all kinds of transmission performance problems that can eventually result in internal damage. The system may recognize the resulting abnormal vehicle operation and turn on the transmission warning light.
Keep in mind that your car’s transmission doesn’t burn fluid the way an engine might burn oil. If the transmission fluid level is low, there’s a leak somewhere that needs to be fixed.
Internal Transmission Failure
Automatic transmissions are complex assemblies with many internal components (i.e., clutch packs, planetary gear sets, etc.). When one or more of those components fails, the system may recognize the corresponding abnormal vehicle operation and turn on the transmission warning light.
Shift Interlock Issues
The transmission warning light doesn’t always mean there’s a problem with the transmission itself. On some BMWs, for example, the light may illuminate when there’s an issue with the shift interlock system—a feature that prevents the driver from taking the gear selector out of “park” without the brake pedal depressed.
Valve Body Problems
Traditional automatic transmissions and most continuously variable transmission (CVTs) have a valve body. The valve body contains a collection of passages that direct fluid flow through valves to various parts of the transmission. Modern valve bodies often contain the transmission control module (TCM) and various other electronics, as well.
An issue with the valve body can prevent the transmission from operating as it should, which can trigger the transmission warning light.
Torque Converter Issues
Most automatic transmission designs use a torque converter. The torque converter acts as a fluid coupling device between the engine and transmission. A lockup clutch inside the converter provides a mechanical link between the engine and transmission under certain conditions.
Over time, the torque converter can begin to cause problems, such as shuddering and slippage. In some instances, a bad converter can even come apart and contaminate the transmission with debris. Problems such as these may cause the transmission warning light to turn on.
Problems With Electronics and Computer Controls
Like most every other part of a modern car, the transmission is managed by a control module that gets its information from various sensors. The module communicates with other modules over a data network.
Sensor, module, and data network problems can cause a variety of issues that turn on the transmission warning light. Other electrical problems—ranging from damaged wiring to a faulty shift solenoid—can potentially turn on the transmission warning light, as well.
Should You Continue to Drive With the Transmission Warning Light On?
Because the transmission warning light can come on for a variety of reasons, some of which are significant problems, you should not continue to drive your vehicle with the light illuminated. You (or your mechanic) should diagnose and repair the problem right away to prevent further damage to the vehicle.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.