The Light Show

If it starts to look like a Christmas tree, you could have problems

On just about every vehicle out there, the moment you first turn the key on, but before you actually crank the engine, a multitude of lights will light up the instrument cluster like a Christmas tree. As soon as the engine cranks and starts many of the lights shut off right away and the rest will shut off within a few seconds. If one of these lights stays on then you may have a problem. Knowing what the problem is and how severe the problem might be is a task left to professionals, but if you know what each one of these lights refers too, and you understand the various ways in which they may illuminate, then it will help you to know if you can ignore it for a day or two until you have a chance to take it into the shop, or if it means that you must pull over right away before you do major damage to some system on the vehicle.

Sometimes these lights are called “dummy lights” this name comes from the idea that when the light comes on it is almost as if it is saying, “you’ve got a problem dummy, pull over now.” Knowing each MIL (malfunction indicator lamp) that applies to your vehicle really is a must.

Check Engine Light

This light really doesn’t have much to do with the engine itself and has more to do with the engine control systems and the emissions control systems. Sometimes the light might say “service engine soon” or sometimes it might just be an outline of an engine and not have any words around the light at all. Getting rid of words is something that has become more common recently in vehicle controls and instrumentation because it means that the light can be understood regardless of the language of the driver.

When the Check Engine MIL illuminates it means that a failure in the engine controls, or the emissions controls, has occurred that will cause an increase in the emissions from the vehicle. This is bad for obvious reasons, but even if you don’t really care about the emissions from your vehicle, it also usually means that the vehicle is less efficient and you may also notice a loss of power or reduced fuel economy.

When the light illuminates the computer that controls the engine will also store a diagnostic trouble code that relates to the failure. This code can be read from the computer using a special scan tool the will communicate with the computer to extract all sorts of information related to the code and the failure. This code is a clue for the technician to use to determine where the exact failure has occurred. Some people are under the impression that the technician can hook up the car to some kind of magical machine, and the machine will tell them everything that’s wrong. This is not true. The scan tool provides clues, but it takes a good diagnostician to piece the clues together.

This is why it costs so much money just to have a technician read the codes and do a bit of diagnostic work. If you ever go to a repair shop or any other place, e.g. parts store, quick lube, and the like, and they say that they will tell you why the light is on for free, remember that you get what you pay for. If they really aren’t going to charge you to hook up their scan tool then they really aren’t going to give you much useful information. In the case of parts store, they will be more than happy to sell you a part on the off chance that it might fix the vehicle. Of course if you go and put that part on your car and it doesn’t fix it, don’t count on the parts store refunding your money for the part.

If the check engine light comes on it almost never means that the vehicle must be pulled over to the side of the road immediately, it usually means that the system ought to be checked out as soon as possible. If the light comes on but the vehicle seems to be running just fine then there is no big hurry to take any action. Just make sure to schedule an appointment with your mechanic as soon as possible. If the MIL comes on and you notice a difference in the way the car is running such as, a loss of power, stumble or hesitation, vibration or excessive noise, then the situation is more urgent. Drive the car home or to the shop as soon as you can and don’t drive it anywhere else.

If the light illuminates and blinks off and on rapidly, pull your car over and shut it off as soon as you can get to a safe place. The blinking light is meant to instill a greater sense of urgency to get the driver to take the appropriate action. The blinking light also indicates what is referred to as a type A misfire. This is when at least one of the cylinders of the engine stops firing altogether. This is something that can destroy the catalytic converter. The “cat,” as it is commonly called, is an emissions control device located in the exhaust system. When the cat is destroyed it may cost over $1000 just to fix it, let alone the thing that caused the misfire which ruined the cat. This is why the blinking check engine light should never be ignored.

When the check engine light comes on it means something is broken and must be fixed. Some people say that the light on the car just comes on sometimes and shuts itself off later and that this is normal and no big deal. Well it may be normal and the driver might think that it’s no big deal but it still means that something is broken.

Brake Light

The brake warning light can take on many different forms. Sometimes the word “brake” is used all by itself and sometimes there will be some kind of symbol used with brake, or sometimes it’s just some kind of symbol. The brake warning light will usually indicate any one of three and sometimes four different things. The different possibilities will ultimately depend on the make and model of the vehicle in question.

When the parking brake is applied the brake light will come on and stay on until the parking brake is released. This is easy to understand and usually no big deal to figure out, but some people might forget and they will actually drive their vehicle several miles before they realize what is going on.

The brake light could like anyone of these or all of them together.

The second thing that the brake light comes on for is low brake fluid level in the master cylinder. This is really easy to check. Simply remove the cap on the reservoir look inside. If the reservoir is translucent, just look at the level through the plastic sides. High and low levels are indicated on the side of the reservoir. If the fluid is low then don’t just add fluid and call it good. Many times when the fluid level falls to a low level it is an indication of worn out brake linings. As the linings in the disc brakes wear, the fluid flows into a larger and larger space behind the caliper piston. This will cause the level in the reservoir to go down. When the pads are replaced and the calipers reset, the fluid is pushed back into the reservoir.

The third thing that causes the brake light to come on is a pressure imbalance in the brake hydraulic system. Usually if the light comes on for this reason, the brake pedal will sink much lower and it will take longer for the vehicle to stop. All cars actually use two separate hydraulic systems to apply the brakes. One system applies the brakes on two wheels, and the other system applies the brakes on the other two wheels. If there is a leak in one of the systems, the pressure in the other system will activate a switch that will cause the light to come on. To repair this kind of failure a professional may be needed and it is obviously not safe to drive the vehicle.

The last thing that will cause the brake light to come on only applies to some cars, usually European cars. This last thing is worn out brake pads. The brake pads on most BMW, Mercedes, and Volkswagen vehicles have a sensor in them. This sensor is tripped when the pads wear thin and it will cause the light to come on. Sometimes the pad wear light may be different from the regular brake warning light.

Battery Light

The battery light is sometimes called the charging system indicator. Either way, the light itself is usually shaped like a battery with a plus and a minus symbol on it. This light will come on when the voltage in the battery or charging system is too low. Many vehicles with a voltmeter in the cluster will also still have a battery light. When the key is turned to the on position but the engine is not started, this light comes on because it is sensing battery voltage only which, without the engine running, will always be lower then what the light and its control systems like to see. When the engine is started the alternator begins to turn and do its job. This will cause the voltage in the battery and charging system to go to about 14 volts if all is functioning correctly. This voltage will cause the battery light to turn off.

Battery light

If this light comes on and stays on while you are driving down the road, it means that the alternator might not be working, and there is a possibility that the vehicle could stall. When the alternator isn’t working, things like the fuel pump and ignition system are drawing all of the power they need directly from the battery, and the battery isn’t getting charged. Eventually the battery will go dead and the engine will die. This won’t hurt the car but it will leave you stranded. Once the engine stalls it isn’t going to even want to crank. If you can drive home or to the shop before the car dies, it is okay to do so, just make sure that you conserve electrical power in the vehicle by turning off all electrical accessories. If you are driving at night then don’t even try and drive the vehicle. Just pull over safely and call a tow truck. The head lights draw so much power that you probably won’t make it very far and it’s not safe to drive with the headlights off.

Oil Light

This is a light that should not be ignored whatsoever. The oil light comes on when the key is first turned on and shuts off a few seconds after the engine starts. This light comes on when oil pressure drops to zero. This is why it’s on when you first turn the key on. Without the engine running there is never any oil pressure. Vehicles that have an oil pressure gauge will always still use an oil pressure light.



Oil pressure light

When this light comes on you must pull over IMMIDIATELY and turn the engine off. This does not indicate low oil level, or that the oil needs to be changed, or that you need to check it. The time for checking the oil is past, this means pull over dummy or you will blow up your engine. Way too many people who neglect the maintenance on their car also turn out to be the same people that keep driving to the next freeway exit when they see this light, but of course it is too late. Once this light comes on solid you have a few seconds before damage occurs and maybe a minute or two, depending on the load on the engine, before the engine comes undone.

Oil level light

Some vehicles have a “Low Oil” light but this is something totally different. If the low oil light comes on it means that you need to add some oil, but you are not really going to hurt anything by driving to a place where it is safe to pull over and have a look. Most cars don’t have a low oil light so don’t assume that yours does. This is the kind of light that you will never see unless your oil level is actually low.

TPMS Light

The Tire Pressure Monitoring System (TPMS) MIL is something that is relatively new. Because of the Firestone Tire/Ford Explorer, scandal of the last decade, Congress came up with a mandate that said that every vehicle sold in the US should have some kind of tire pressure monitoring system installed from the factory starting with the 2008 model year. Many manufacturers started putting these systems on long before the mandate.

See this light, check your tire pressure

The system consists of a tire pressure sensor located in each wheel assembly. The reading taken by each sensor is transmitted wirelessly to a receiver which sends the signal to a processor that monitors the pressure and temperature of each tire. When the computer senses that a tire is too low, it will illuminate the TPMS light. In order to make the light turn off, the tire must inflated to the proper pressure. Some systems will turn the light off as soon as the pressure is set to specification, and some must have the pressure set and then be driven several feet before the light will turn off.

When this light comes on check your tire pressure. Tires that are under inflated can be dangerous because the tires can get very hot and could fail. These systems will usually not turn the light on for over inflation, but over inflation can be dangerous as well. Many systems will not just turn on the TPMS light but they also have an information display that will tell you which tire is low.

A tire pressure sensor mounted to the inside of a rim.

Because TPMS is a computer controlled system, it is capable of some self diagnosis and as such it may illuminate the TPMS MIL if there is a failure in the system. On most vehicles when there is a failure in the monitoring system and not necessarily a low tire, the TPMS light will come on and blink for the first few minutes after the engine is started. This means that a trouble code is stored and a scan tool is needed to extract the code from the control unit. The sensors in the wheels are all battery powered and they only last so long. When one of the sensor batteries fails it will cause a trouble code to set and the TPMS light to come on. Most TPMS systems also have a reset button that might need to be pressed if all of the tires are set to the proper pressure and the light will not turn off. This might happen as the seasons change because of the way that temperature and pressure are related.

ABS Light

ABS stands for Anti-lock Braking System. The ABS light might say ABS, it might have the brake symbol with ABS in the middle, or it might say “Anti-Lock.” ABS is a system integrated into the vehicle braking system that prevents the brakes from locking up, causing the car to skid and actually increasing the stopping distance. This system uses speed sensors at each wheel that send a signal to a computer indicating the rate of deceleration for the wheel in its rotation. If the wheel stops rotating, the computer can pump the brakes to that wheel alone and prevent the wheel from locking up.

Because this is a computer controlled system like everything else on the car, it is capable of monitoring its own systems and alerting the driver if a problem is found. Once again the computer stores a trouble code that indicates what might be going on with the system. Other systems such as traction control and anti-skid control are very much related to the ABS system. These two systems might have their own MILs that may illuminate together with the ABS light if there is a failure that affects the operation of any or all of these systems. If any of these lights are on it might also mean that the corresponding system will not work, or might not work very well. Most of the time, the brake warning indicator comes on with the ABS light.

SRS Light

The Supplemental Restraint System usually refers to the airbags on the vehicle but with modern restraint systems it could also refer to the seats or the seat belts since they have passive restraint systems integrated into them as well. The SRS light might say SRS, Restraints, or have a picture of an airbag inflated in front of the figure of a person sitting in the car seat. Computer controlled system, trouble code, airbag might not work, you can see a pattern forming here. The SRS system runs a system check every time the key is turned on. The light will stay on during the check and will shut off if no problems are found. This light might not shut off for 5 to 10 seconds after the vehicle is started. Some SRS lights will blink for several seconds during the check and if a problem is found could continue to blink for a minute or two and then stay on permanently.

Coolant Light

Coolant temperature light

Used on vehicles that lack a temperature gauge. The light comes on when the engine temperature gets too hot. Engine should be shut off to prevent damage to internals. Some vehicles have a coolant level light. This might look similar but indicates low coolant in the radiator or the coolant expansion tank.

Maintenance Required Light

Sometimes this will be indicated with words, sometimes it will be indicated with a small wrench symbol. This is a light that comes on to indicate an interval of mileage or time, and indicates that some kind of vehicle service is required. This light can usually be reset without any special tool, but the procedure might not be listed in the owner’s manual. Some vehicles have a maintenance light that says “Service Vehicle Soon,” this should not be confused with the Service Engine Soon light that was mentioned above.

Other Lights

Many other lights can be found on many different types of vehicles. If you are not sure what lights your vehicle has or what those lights mean, check your owner’s manual. The last thing you want on a road trip is an unknown light coming on. You won’t know what it means and you won’t know whether you can continue on your way, or stay put until you get it fixed. No matter what, never forget that lights mean things. Anytime you see one there is a reason that it came on.