Indicator lights are used to convey important information to the driver, such as problems with the vehicle (low fuel, for example) or systems that are in use (such as cruise control). The symbols used can vary by manufacturer, so check your owner's manual for the most accurate information.
When the ignition is first turned on or the car is started, all dash indicator lights should come on and/or flash for a few seconds for a bulb check. Most (if not all) of these lights should then turn off on their own. If a light stays on after the bulb check is complete, or comes on when the car is driven, the vehicle's computer has sensed a fault within that system.
Note that the oil pressure and charging system indicator lights will be on any time the key is on and the engine is not running. This is normal. They should be off when the engine is running.
Indicator Light Color
The color of an indicator light is used to illustrate the severity of a fault. While symbols may vary, the meaning behind the colors are relatively universal.
Green or blue often indicate a system that's currently in use. Examples include cruise, turn signals, high beams, and fog lights.
Yellow or orange indicate that a system will need service in the near future. The vehicle can likely still be driven, but the driver may need to be cautious.
Red indicates a severe fault with a system or a potential safety concern. Depending on the system indicated, the vehicle should not be driven.
Flashing Indicator Lights
Regardless of color, indicator lights that are flashing denote a sense of urgency.
If the check engine light is flashing, a severe misfire is detected. The vehicle should not be driven or damage to the catalytic converter(s) could result. Have the vehicle serviced as soon as possible.
Note that on many vehicles a yellow slip indicator light will flash when the system is actively assisting with traction control. This is normal and does not indicate a fault, and is done to alert the driver to slippery road conditions. It typically looks like a car with skid marks behind it, but it could also be a triangle with a circling arrow around it and an exclamation point inside.
If a fluid level indicator light comes on intermittently and only briefly when driving the vehicle (such as when making a turn), the fluid level is getting close to being low. This is commonly seen on washer fluid, fuel, brake fluid, and oil lights. Check the level and add if necessary.
What to Do When an Indicator Light Comes On
As a general rule, if an indicator light comes on you should either check the system if you can or get the vehicle serviced. Although indicator lights, their meaning, and what to do when they come on could probably be an entire book by itself, there are a few important things to note about some of the most common indicator lights you could encounter:
If the red airbag (SRS) light comes on, it means there's a fault with the airbag system and it may be disabled. This is a safety concern as the airbags will likely not deploy in the event of an accident, so have the system checked.
If the red brake light comes on, pull over as soon as safely possible. First check that the parking brake is fully released. In a number of vehicles, the parking brake and low brake fluid level circuit share the same warning light. If the light goes out after releasing the parking brake, the vehicle is safe to drive. If the light stays on after you try releasing the parking brake, then check the fluid level. Add if necessary, and then check for a firm brake pedal. Check for brake fluid leaks around the car. Do NOT drive the car if it is leaking brake fluid or has a soft or sinking brake pedal – have it towed. Even if no leaks are visible and the light goes off after adding fluid, have the vehicle's brake system serviced as soon as possible.
If the red charging system (battery) light comes on, there is an issue with the vehicle's charging system and the car will loose power in the very near future. Drive home or to a service center immediately, turning off all unnecessary electrical systems – the climate control, radio, headlights if not driving at night, etc. Drive time with a faulty charging system may be up to 90 minutes, but it could be much less. The vehicle will need service.
If the red engine temperature warning light comes on, there is a high likelihood of severe engine damage due to overheating. Pull over as soon as safely possible and shut off the engine. Let it cool off for at least 30 minutes or more, then check the coolant level (remember, never open the radiator cap when the engine is hot). Add if necessary and check for leaks. If you see no coolant leaks at this point you can try to continue driving if absolutely necessary, but watch your temperature gauge and be ready to pull over and let the car cool off again if needed. However, having the vehicle towed would be ideal as it would significantly reduce the risk of engine damage.
If the red oil pressure light comes on, shut off the engine as soon as safely possible. The oil pressure or oil level is low to the point that engine damage could occur. Check the oil level – if it's extremely low, add oil. Otherwise, don't start the engine and have the vehicle towed.
If the yellow TPMS (tire pressure monitoring system) light comes on, one or more tires is low on air. Check your vehicle's tire pressure as soon as possible, and add air if necessary. If your tire pressure is up to specifications and the light still stays on, have the vehicle's TPMS system serviced.
No Indicator Lights Means No Issues, Right?
Just because there are no indicator lights illuminated on your dashboard does not mean that you have nothing to worry about. Indicator lights are a warning system, and are not meant to be a replacement for checking your fluid levels or having your vehicle serviced regularly.