Brake Lights. If the light is on all the time, it could mean you simply forgot to release the parking (emergency) brake. The brake warning light remains on when the brake is set as a reminder. If the brake warning light remains on when the parking brake is released, then something is amiss.
In some cases, the brake warning light may remain on if the switch on the parking brake pedal or lever is misadjusted. Nothing is wrong with the brakes and a simple adjustment should fix the problem. If the brake warning light comes on when you apply the brakes, or is on continuously, it means that hydraulic pressure has been lost in one side of the brake system or that the fluid level in the master cylinder is dangerously low (due to a leak somewhere in the brake system). In either case, the fluid level in the master cylinder should be checked. Adding brake fluid to the master cylinder reservoir may temporarily solve the problem. But if there's a leak, the new fluid will soon be lost and the warning light will come back on. Brake fluid leaks are serious because they may cause the brakes to fail! So avoid driving the vehicle until the system can be inspected to determine what's wrong. Leaks can occur in brake hoses, brake lines, disc brake calipers, drum brake wheel cylinders or the master cylinder itself. Wet spots at hose or line connections would indicate a leak that needs to be fixed. Leaking brake fluid can also contaminate the brake linings, causing them to slip or grab. The uneven braking action that results may cause the vehicle to veer to one side when the brakes are applied. Brake shoes or pads that have been contaminated with brake fluid cannot be dried out and must be replaced. Brake Warning Light Circuit The brake system is divided into two hydraulic circuits. On most rear-wheel drive vehicles, it is divided so one circuit applies the front brakes and the other applies the rear brakes. On front-wheel drive cars and minivans, the system is usually split diagonally. One circuit works the right front and left rear brake, and the other works the left front and right rear brake. This is done for safety purposes so if one circuit loses all its brake fluid and fails, the vehicle will still have one remaining circuit to apply two wheel brakes. Usually located on the master cylinder or the brake lines exiting the master cylinder is a "pressure differential" switch. If either brake circuit develops a leak and loses its fluid, the difference in pressure when the brakes are applied will trip the differential switch causing the brake warning light to come on. Abs Warning Light On vehicles equipped with antilock brakes (ABS), a second warning light is provided to warn if a problem occurs within the ABS system. The ABS lamp comes on when the ignition is turned on for a bulb check, then goes out after the engine starts. If the ABS warning light remains on or comes on while driving, it indicates a fault has occurred in the ABS system. What happens next depends on the nature of the fault. On most applications, the ABS system disables itself if the ABS warning light comes on and remains on. This should have no effect on normal braking. Even so, ABS will NOT be available in an emergency situation or when braking on a wet or slick surface. CAUTION: If the brake warning light also comes on and remains on while the ABS warning light it on, it signals a serious problem. Your vehicle may not be safe to drive. The brakes and ABS system should be inspected immediately to determine the nature of the problem! If the ABS light comes on momentarily then goes out, the nature of the problem is usually minor and the ABS system usually remains fully operational. Some vehicle manufacturers call this kind of fault a "nonlatching" fault (meaning it isn't serious enough to disable the ABS system). Regardless of the type of fault that occurred to trigger the ABS warning lamp, a special "code" is recorded in the ABS module's memory to aid in diagnosing the problem. On some vehicles this code can be retrieved by putting the ABS system into a special diagnostic mode. The code is then flashed out through the ABS warning lamp. The code number refers to a diagnostic chart in a service manual that must be followed to pinpoint the faulty component. On other applications, a special "scan tool" must be plugged into the vehicle's diagnostic connector to read out the fault code. Diagnosing ABS problems requires a fair amount of knowledge and expertise (as well as special equipment in many applications), so this job is best left to a competent professional. My temperature warning light is on. Is it okay to drive the car? less you want to risk damaging your engine. When the temperature light comes on, it means your engine is overheating. An engine should not overheat if the cooling system is properly filled and is working normally -- even during hot weather or stop-and-go driving. Sometimes abnormal driving conditions such as towing a heavy trailer during hot weather may overload the cooling system's capacity to control heat, but usually a temperature warning light means trouble. What To Do: Stop driving immediately, pull over to the side of the road, shut the engine off and wait for things to cool down. WARNING: Do not attempt to open the radiator! The radiator contains hot water under high pressure. Opening the cap could allow steam and water to blow out and burn you. There's nothing to be accomplished by opening the cap while the engine is still hot, so let your vehicle sit and cool off. After things have cooled down (wait at least half an hour or more), then you can open the radiator cap and check the coolant level if you think it might be low. Place a rag over the cap first, and slowly turn the cap until it stops at the first detent. This should allow residual pressure to be released. Wait until all pressure has been released before removing the cap the rest of the way. Add water to the radiator if it is low. Actually, you should add a 50/50 mixture of antifreeze and water to maintain the proper freezing, boilover and corrosion protection. But in most cases when this happens, it's an emergency situation and you don't have a jug of antifreeze handy. If that's the case, you'll have to add antifreeze later. Visually inspect the system for leaks. Common leak points include radiator and heater hoses, the water pump and the radiator. Internal leaks (such as a crack in the head or engine) can't be seen and can only be diagnosed by pressure testing the cooling system. If You Don't Stop Driving... If you keep driving an engine that is overheating, it can cause serious damage. The engine may start to knock (caused by detonation), which in turn can cause piston, ring and head gasket damage. As the internal parts of the engine expand from the excessive heat, clearances may be reduced to the point where metal-to-metal contact occurs. Valve stems may gall and stick, and the pistons and camshaft might scuff or seize. Severe overheating also creates tremendous thermal stress in the head(s) and block. This, in turn, may lead to cracking and/or warpage. This is a common problem with overhead cam engines that have aluminum heads. The only vehicle that can be "safely" driven when the temperature warning light is on a late model Cadillac with a Northstar V8 engine. Cadillac engineers designed the engine control system to automatically deactivate half of the engine's cylinders if it senses an overheating problem. This reduces the heat (and power) being generated by the engine, and it allows the "dead" cylinders to pump air through the engine for internal cooling. The system is designed to provide a "limp-in" mode so the vehicle can be driven to the nearest service facility or Cadillac dealer for repairs. It is not designed for continuous driving. My alternator warning light is on. Can I keep driving anyway? Yes, but probably not for very long. If the alternator warning light is on, it means your charging system is not producing enough current to meet the electrical needs of your vehicle and to keep the battery charged. That, in turn, means your vehicle is running on borrowed time off the battery alone. You can keep on driving as long as the battery has enough juice left in it to keep the ignition system, fuel injectors, fuel pump and other electrical accessories working. But sooner or later, the battery will run down and your engine will die. How long this might take is anyone's guess. If you're driving during the daytime and aren't listening to the radio or running the air conditioner, the battery along might keep you going for four, five, six or more hours. On the other hand, if its nighttime and you have the lights on, the heater or air conditioner and radio, you might run the battery dead in an hour or two. A warning light should not be ignored. It usually means something has failed and needs to be fixed -- the sooner the better in this case. Sometimes the alternator warning light will come on, (or the amp or voltage gauge will show discharge) when nothing is really wrong with the charging system. It's a gauge or light problem. One way to tell is to turn on the headlights. If the headlights shine with normal intensity and do not change as you rev the engine, all's well with the charging system and the problem is in the warning light or gauge circuit. But if the lights are dim or get brighter as you rev the engine, you have a charging system problem that requires further diagnosis. Any of a number of problems can cause the alternator warning lamp to come on. If the alternator drive belt is slipping, has broken or flipped itself off the pulley, the alternator will cease to produce current and the warning light will come on. If the regulator that controls the alternator's output has failed, the warning light will come on. And if there's a wiring problem in the charging circuit, the light will come on. My oil pressure warning light is on. What should I do? Don't ignore it. An oil pressure warning light (or low gauge reading) means one of two things: either your engine has dangerously low oil pressure (for a variety of reasons which we'll get to in a minute), or the oil pressure sending unit that triggers the warning light (or operates your gauge) has failed. The question here is whether you have a serious problem or a minor one. First, do not keep driving if the oil warning light is on or your oil pressure gauge has dropped. Stop the engine, let it sit for a few minutes, then check the oil level. Is the level low? If the oil level is down more than two quarts or no oil is showing on the dipstick, adding oil to bring the level back up to the full mark may be all that's necessary to make the light go out. Just keep your fingers crossed that you haven't damaged the engine from running it too low on oil. If you hear rapping or knocking noises the engine starts, you're too late. The damage is done and now you're stuck with the consequences. Note: On some late model vehicles, the warning light will come on (or a message will appear) if a sensor in the oil pan detects a low oil level. The light is supposed to come on before the level gets low enough to cause any damage. If your oil level was low, it means your engine is either leaking oil or burning it. Leaks can be fixed by finding and replacing leaky gaskets and seals. Sometimes the oil filter will leak if it isn't installed or tightened properly. But an oil burning problem means the valve guides, rings and/or cylinders are worn or damaged and more costly repairs are needed. If the dipstick shows a full oil level, then low oil obviously isn't your problem. The oil pressure may be low because of a worn or broken oil pump, a plugged oil pickup screen in the engine's crankcase, possibly a plugged oil filter or excessive bearing wear. Or, the oil pressure may be fine but the oil pressure sending unit has failed. Further diagnosis will be required to determine what's wrong. Should you attempt to drive your vehicle home or to a service facility? It's risky. If the problem came on suddenly, your engine does not have a lot of miles on it (less than 60,000) and you noticed no unusual noises (no valvetrain clattering or engine knocking), there's a good chance that all that's wrong is the sending unit. But, there's no way to know for sure without actually checking the engine's oil pressure with a gauge, or replacing the sending unit to see if a new unit makes the light go out. If the problem is only the sending unit, your engine still has oil pressure and you can continue to drive it until the sending unit can be replaced. But, if you're wrong you risk ruining your engine. If you think you might have a low oil pressure or oil delivery problem because of a bad oil pump or one of the other problems we mentioned, do not drive your vehicle. Doing so only increases the probability of further engine damage. Have the vehicle towed to a service facility for repairs. My "Check Engine" light is on. What does it mean? It means your vehicle's onboard computer system has self-diagnosed some kind of problem. The "Check Engine" light, which is also called a "Malfunction Indicator Lamp" (MIL) or "Service Engine Soon" (SES) lamp, is there to signal you when a problem occurs that may require attention. This can include anything from a momentary hiccup that has has little or no noticeable affect on engine performance or driving safety to a failure of a major electronic component. There's no way to know what the light means without running a diagnostic scan on the system to determine the nature of the fault. As a rule, a continuous Check Engine light usually signals a "hard fault" or failure that has occurred. If the light comes on and off, or only blinks momentarily, the problem may be minor or intermittent in nature. To help identify the problem, it helps to make a mental note of the conditions that occurred when the light came on. Where you driving at a certain speed? Accelerating or slowing down? Shifting gears? Onboard diagnostic systems are very complex and require a fair amount of expertise as well as special tools to troubleshoot. To find out what's wrong, a technician has to "get into" your system through a diagnostic connector which may be located under the dash, under the driver's seat or in the engine compartment. The diagnostic connector serves as a port of entry for accessing information and/or for putting your vehicle's computer system into a special diagnostic mode for further testing or displaying "fault codes". Fault codes are numeric codes that are generated when a problem is detected. If a sensor circuit reads out of range or some electronic component fails to respond to a command from the computer, the computer recognizes it as a fault and records a number that corresponds to the nature of the problem. The technician must then retrieve the code and refer to specific diagnostic chart or "fault tree" that gives him the step-by-step checks he has to perform to isolate the failed component. It can be a very time-consuming process depending on the nature of the problem. Usually the process works but sometimes it doesn't. An intermittent fault can be very difficult to track down, and may require repeated attempts to repair it.
