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.

Headlight Replacement: One of the most common lighting system repairs is replacing the headlight. After a period of time the filament may burn through or the lens may be broken. Before the headlight is replaced, however, check the condition of the fuse. If it is good, you may also want to use a voltmeter to test the circuit. Service tip: If it is necessary to replace the headlight lamp often, check the charging system. A too-high voltage output will cause the filament to burn hotter than it is designed to burn and will shorten the life of the lamp. The procedure for replacing the headlight differs depending on the type of bulb used. Most conventional sealed-beam and halogen sealed-beam headlights are replaced in the same manner. Composites require different procedures. Always refer to the service manual for the vehicle you are working on. Because of the construction and placement of the prisms in the lens, it is important that the headlight is installed in its proper position. The lens is usually marked 'TOP' to indicate the proper installed position.

Sealed Beam:
To replace a sealed-beam headlight:
1. Place fender covers around the work area.
2. This type of replacement usually requires the removal of the bezel which is the retaining trim around the headlight itself.
3. Remove the retaining ring screws and the retaining trim . Do not turn the two headlight aiming adjustment screws.
4. Remove the headlight from the shell assembly.
5. Disconnect the wire connector from the back of the lamp.
6. Check the wire connector for corrosion or other foreign material. Clean as needed.
7. Coat the connector terminals and the prongs of the new headlight with dielectric grease to prevent corrosion.
8. Install the wire connector onto the headlight prongs and place the headlight into the shell assembly. When positioning the headlight, be sure the embossed number is at the top.
9. Install the retainer trim and fasteners.
10. Check operation of the headlight.
11. Check headlight aiming as described in the next section.
12. Install the headlight bezel.

It is not recommended that halogen sealed-beam and standard sealed-beam headlights be mixed on the vehicle. Also, if the vehicle was equipped with halogen headlights as original equipment, do not replace the headlights with standard sealed beams. Doing so may result in poor light quality. Because the filament of the halogen lamp is contained in its own bulb, cracking or breaking of the lens does not prevent headlight operation. The filament will continue to operate as long as the filament envelope has not been broken. However, a broken lens will result in poor light quality and should be replaced for the safety of the customer.

Composite:
To replace a composite headlight:
1. Place fender covers around the work area.
2. Remove the wire connector from the bulb.
3. Unlock the bulb retaining ring by rotating it 1/8 of a turn.
4. Slide off the retaining ring from the base.
5. Gently pull the bulb straight back out of the socket. To prevent breaking the bulb and locating tabs, do not rotate it while pulling.
6. Check the wire connector for corrosion or other foreign material. Clean as needed.
7. Coat the connector terminals and the prongs of the new headlight with dielectric grease to prevent corrosion.
8. Place the new bulb in the socket . The flat part of the base should face up. It may be necessary to turn the bulb slightly to align the locating tabs.
9. The mounting flange on the bulb base should contact the rear of the socket.
10. Install the retaining ring over the base and lock the ring into the socket.
11. Reconnect the wire connector to the bulb. It will snap and lock into position when properly installed.
12. Check headlight operation.
13. Check and adjust headlight aiming as needed.

Be careful not get any of the dielectric grease onto the bulb. The bulb's life will be shortened. Also whenever you replace a composite lamp, care must be taken not to touch the envelope with the fingers. Staining the bulb with normal skin oil can substantially shorten the life of the bulb. Handle the lamp only by its base. Also dispose of the old lamp properly.

Headlight Aiming The headlights should be checked for proper aiming whenever the lamps are replaced. Proper aiming is important for good light projection onto the road and to prevent discomfort and dangerous conditions for oncoming drivers. Correct headlight beam position is so critical that government regulations control limits for headlight aiming. For example, a headlight that is misaimed by one degree downward will reduce the vision distance by 156 feet. You should have your headlights tested at your local service station.

One is an accidental electrical short. The wires that run to the air bag are routed down the steering column and under the dash along with dozens of other wires. If you're doing electrical work under the dash and short out a hot wire to one of the wires in the air bag circuit, it could result in a rather loud and unexpected boom from the air bag. The bag deploys with explosive force, which might injure you if you're in the way. The counterforce generated by the bag is designed to protect occupants who are wearing seat belts and facing forward in an upright position, not someone who is working on the car or just sitting behind the wheel.

To prevent this from happening, always disconnect one of the battery cables before doing any electrical work or working on any part of the air bag system (including the steering wheel). Emergency rescue personnel such as paramedics and police officers are trained how to deactivate air bags. This may be necessary if a person is trapped in a vehicle with an air bag and the air bag has not deployed. The last thing they want is the air bag exploding as they're trying to extract an injured person from the wreckage. Disconnecting the battery doesn't necessarily deactivate the air bag because the control module often contains an internal battery that keeps the system armed for up to several minutes. This is actually a safety feature that allows the air bag to work in case the battery cables are severed during a crash.

Many air bag equipped vehicles have a special orange or yellow connector at the base of the steering column that can be disconnected to temporarily disable the air bag. The ignition must be off when this connector is disconnected or reconnected. The connector may have a tag labeled SRS (Supplemental Restraint System) connector or SIR (Supplemental Inflation Restraint) connector.

Another situation where an accidental air bag deployment may occur is when plowing snow with a truck or sport utility vehicle fitted with a snow blade. Due to the severe jolts or bumps that may occur when ramming into things with a blade, the air bag system should be deactivated prior to plowing by removing the system fuse or unplugging the air bag connector(s) per the vehicle manufacturer's instructions. The same situation may occur when off-roading in a four-wheel drive vehicle. Again, deactivating the air bag will prevent jolts and bumps from setting it off.