Transmission warning light: Everything you need to know

The transmission warning light indicates there is a transmission issue that could be related to fluid level, temperature, or pressure.

It’s important to know the meaning of this car dashboard warning light to ensure you keep your transmission in good working order - and avoid hefty repair bills.

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What is a transmission warning light?

The transmission warning light appears when something is wrong with your transmission or gearbox. For this reason, this light is sometimes also referred to as the ‘gearbox warning light’.

The symbol used varies depending on the make and model of your vehicle, but it’s a visible light with a distinct symbol, so you shouldn’t miss it. Common variations of this symbol include:

A gear and another gearwheel, encircling a thermometer, or an exclamation point.
Some manufacturers use ‘D’ or other gear-related letters next to an exclamation mark, and others use a wrench.

Common causes for a transmission warning light

Overheating is one of the most common triggers for the transmission warning light. Low transmission fluid, a blocked cooler, or an internal transmission issue can all contribute to overheating. Treat an overheating transmission like an overheating engine; stop driving immediately, allow your transmission to cool down, and ask a professional to look at it.
Low transmission fluid can also cause the light to illuminate. When transmission fluid is low, this will cause your transmission to run improperly, which can cause internal damage. It’s important to note that transmission fluid doesn’t burn off the way engine oil does. So, if you have low fluid, this probably indicates that you have a leak. Check for a transmission fluid leak by looking for a dark or bright red puddle under your car.
Transmission fluid can become contaminated by debris, metal particles, or dirt, which can lead to clogs and other problems within the transmission system.
Electrical issues such as shift interlock failure can also cause the transmission light to come on. Some cars with automatic transmissions feature a shift interlock system which requires you to press the brake first to shift out of ‘park’. If this system malfunctions, the light can come on. Wiring problems, loose connections, and electrical malfunctions within the transmission control module (or associated components) can also cause the light to come on.
Faulty sensors can also be the cause of a flashing transmission light. Modern vehicles rely on a variety of sensors that monitor the transmission’s performance. When any of these sensors malfunction, or provide incorrect data, the warning light may be triggered.
When towing heavy loads (especially when they exceed your vehicle’s towing capacity), the transmission can become strained, leading to overheating.

Putting undue pressure on your vehicle can lead to other transmission issues, such as worn-out clutches, damaged gears, and malfunctioning torque converters. This can cause erratic shifting - and trigger the transmission warning light.
Problems with the vehicle’s onboard software can also cause alerts, some of which may be false. A mechanic may need to carry out diagnostic checks before rectifying these issues.

This warning light can also be prompted by a failure to keep up with your vehicle’s maintenance:

If you’re experiencing any difficulty or delays when shifting gears, or hearing unusual noises, the components within your transmission are likely to be worn.
Any shuddering or stuttering when you’re driving can indicate an issue with torque control.
Visible transmission fluid leaks or overheating can also indicate issues with your transmission.

Can you drive with the transmission warning light on?

We strongly advise against driving with the transmission warning light on, because it indicates there is a problem within the transmission system. Therefore, if you continue to drive, this could pose a safety risk, cause further damage, and leave you with a costly repair bill.

You could also trigger limp mode, which is a safety feature in cars that activates when the computer finds a problem within a critical system (such as the transmission system). The purpose of limp mode is to protect the car by reducing power and slowing it down, which will allow you to get to a safe place whilst minimising damage.

Therefore, when the transmission warning light comes on, you should only drive as far as strictly necessary. To err on the side of caution, pull over as soon as possible, and arrange for your car to be towed to a garage.

How to diagnose transmission problems

Check the fluid: Check the transmission fluid on the dipstick for fluid levels, cloudiness, thickness, or a foul smell.
Listen for noise: Faulty manual transmissions will make abrupt grinding noises when shifting gears, whilst an automatic transmission might whine, hum, or buzz.
Check for a burning smell: A burning smell coming from the engine is a sign of a malfunction, usually overheating fluid.
Look for fluid leaks: Look beneath your car for any puddles of dark or bright red liquid.
Use an OBD-II scanner: Use this device, which plugs into your OBD-II port to access information about your car’s systems and components. These scanners are frequently used by mechanics to read diagnostic trouble codes.

How to fix transmission issues

Top up or replace your transmission fluid.
Fix any leaks.
Repair faulty sensors, or replace them, if repairing isn’t feasible.
Address any electrical issues flagged by the OBD-II scan.
Take your car to a professional mechanic.

Tips for avoiding transmission issues

Check and change your transmission fluid regularly to ensure you always have enough.
Avoid overheating your car, so be conscious when towing.
Make sure to shift gears properly, and drive gently. Avoid accelerating or decelerating too quickly.
Get regular transmission check-ups to help extend the life of your transmission.