Vehicle Warning Lights Explained

Your Vehicle Warning Lights

All late model cars, trucks, minivans, and SUVs are controlled by sophisticated computer systems vehicle warning lights that monitor an assortment of critical components that include, but are not limited to, the engine, drivetrain, emission’s system, electrical system, tire pressures, brakes, airbags, cooling system and suspension. These components are constantly being monitored and adjusted by the computer according to speed, load, engine temperature, gasoline quality, ambient air temperature, road conditions, etc.

When the computer “senses” the car is operating outside of standard parameters, it stores the corresponding trouble code(s) in its memory and triggers a light that appears on the dash to indicate that there is a problem. A technician then needs to connect a scanner to the car’s computer in order to retrieve the fault. This code, however, doesn’t tell exactly what’s wrong or what component is faulty; it only indicates what system is malfunctioning and where the technician needs to start looking.

Knowing what to do when a light appears on your dash can make the difference between a quick and easy diagnosis, and an expensive repair. Here are some of the more important warning lights every driver should be aware of:


Check Engine Light

This light simply means that your vehicle’s on-board computer system detected a problem and stored a fault code. In this respect, there are literally hundreds of reasons why a Check Engine light icon might appear on your dash, but if it’s there, it’s on for a reason and needs to be addressed as soon as possible. Depending on the year, make, and model, it may be related to the engine, emission’s system, or the transmission. More often than not, the fault code points to a problematic circuit, as opposed to a specific component, sometimes resulting in a lengthy process to identify, diagnose, repair. This is also why each car requires an individual approach before the root cause of the problem can be identified and fixed. To avoid potential long-term issues, we strongly recommend that you get it checked at your earliest convenience or risk damaging the engine or expensive emissions components.

Note: Leaving the gas cap off or failing to securely tighten it after filling up is the most common, and inadvertent, customer-induced issue and happens more often than you’d think.


Service Reminder Lights

Also called a Change Oil Soon or Service Soon light, these are as common as check engine lights. The computer’s on some cars track when the oil and filter needs to be changed, which is most often calculated on time and/or mileage and how your vehicle is driven. While there is a lot of debate whether it’s best to regularly change the oil and filter or rely on the computer to tell you, the system should still be reset after each oil change so the computer is reset. In this respect, each manufacturer has a specific method to reset this light; some cars require expensive diagnostic tools, and some require the technicians to simply follow a specific procedure. It’s best to call or visit a reputable shop like Coho if you have any questions.


Other Oil Lights

A steady (non-flashing) or yellow engine oil light icon typically means that there is a general fault within your engine’s oil lubrication system such as a malfunctioning oil pump. Vehicles that do not have an oil level monitoring function should have the oil checked during the next gas stop. If, however, you get a flashing or red oil warning light on your dash, pull your vehicle over immediately and shut the engine off. The best-case scenario is that your engine oil is low or there is a problem with the circuit. The worst-case scenario is you have no oil pressure and risk complete engine failure by driving the car any farther. In this case, it’s best to have the car towed to us.


SRS Light (Supplemental Restraint System)

The supplemental restraint system is your airbag system and is monitored with a variety of active, passive, or pre-safe sensors. The slightest malfunction in this system illuminates the SRS light and if activated, can mean any number of things. For instance, it could be alerting you that a broken part needs to be repaired, or is indicating that a critical circuit was temporarily disconnected (e.g., while you were installing a stereo, alarm, aftermarket seat or steering wheel). Since the SRS system is an important safety feature, it needs to be diagnosed, repaired and reset as soon as possible.


ABS Lights

This warning lamp means your antilock brake system – which keeps you from skidding out of control during braking by limiting your wheels from locking up/skidding – has detected a fault. Simply put, it temporarily disables your ABS system. You can continue driving and still brake and stop normally, but the antilock braking system will not work if you need to make a sudden panic stop or brake on wet or slick surfaces. But you should have the problem diagnosed and repaired at your earliest convenience.

Note: The ABS Warning System does not monitor disc brake pad or disc brake rotor wear. Also, the system is often integrated with traction control and stability systems, all of which are designed to keep you safe during panic stops.


Low Coolant Light

The low coolant Light will come on when the coolant drops below the sensor – generally one to two quarts; i.e., low coolant level. If this light is on, there are a number of possibilities. The most common is a coolant leak. Other common causes include: an electrical fault in the warning lamp circuit, a stuck thermostat, a cooling fan that is not working, a failed water pump, obstructions that block airflow through the radiator, a buildup of scale or sludge inside your cooling system, or overworking your engine or air conditioning system during unusually hot weather. Towing a heavy trailer or prolonged mountain driving may also cause your engine to run hotter than normal. The best course of action is to stop as soon as possible, park it in a safe place, and call for a tow truck.


Charging System

The generator (GEN) or alternator (ALT) warning light is usually an icon of a battery and means there’s a problem with the charging system. While you do not have to stop driving immediately, the time you have left is limited – possibly 30 minutes during the day, or less after dark. The reason is that your car is running exclusively off the battery, so as long as the battery lasts, you will be able to drive. However when the battery’s charge is depleted, the fuel pump, ignition and other powered systems will stop working. The cause may be a failed alternator or generator, a failed voltage regulator (if separate from the alternator), loose or corroded battery cables, or a broken or slipping drive belt. Regardless, your car needs to be inspected and repaired by a professional.


Brake Warning Light

The light usually means you forgot to release the parking brake, or your brake system has a potentially serious hydraulic problem that may make your vehicle unsafe to drive. If the light comes on only while pressing the pedal, one of the hydraulic circuits in the brake system has lost pressure because of a leak with the brake hose, at the disc brake caliper or drum brake wheel cylinder, or there’s a problem with the master brake cylinder reservoir. Many vehicles have a fluid level sensor that will also come on if the fluid level gets too low. If the pedal feels unusually soft or goes to the floor, do not drive the vehicle. Have it towed to us immediately and do NOT attempt to drive it further.