Chevrolet 2010 Impala Service Manual download pdf (Page 142)

REVISIONS MARKED IN BLUE 1/5/2011 2011 Chevrolet Municipal Vehicles Technical Manual

aNtI-Lock brakINg systEm faq | 11

GM offers Anti-Lock Brake Systems as standard or optional

on all North American passenger vehicles and light truck

lines. The computerized Anti-Lock Braking System (ABS) is

designed to keep the vehicle’s wheels rotating as the brakes are

applied to assist the driver in achieving a controlled stop.

Sensors monitor how fast the wheels rotate and feed the data

continuously to the ABS computer. The vehicle’s brakes slow

each wheel as the brake pedal is applied. However, when

ABS is activated due to road conditions, the system repeatedly

releases and applies pressure to the brakes. The wheels

can keep rolling, thus retaining steering ability and enhanced

stability while providing a higher braking force on most

surfaces than a locked wheel provides.

How exactly does ABS work?

In cars without ABS, hitting the brakes can cause the wheels to lock, leaving you unable

to steer the vehicle until you decrease the pressure so the wheels can roll again. With

an ABS, as you apply the brakes, the ABS computer monitors the wheel speed sensor

information. If the computer senses that a wheel is approaching lock up, it sends a

signal to the hydraulic modulator to reduce, then to reapply, brake pressure several

times a second for as long as you maintain firm pressure on the brake pedal. The

process is much like the threshold braking technique used with conventional brakes.

However, ABS does it much faster and more accurately than any driver can, leaving you

free to focus on steering away from obstacles.

Does ABS reduce stopping distances?

Yes, in braking situations where the wheels on a non-ABS equipped vehicle

would lock up, ABS will generally provide shorter controlled stopping distance. The

amount of improvement in stopping distance depends on many factors, including the

road surface, severity of braking, initial vehicle speed, etc. On some surfaces, such as

gravel roads, braking distances can be longer, but you will still have the control benefits

of ABS. The important capability of ABS is control. ABS provides improved vehicle

steerability and stability when braking.

What can affect the ABS advantage?

It is important that you follow the maintenance schedule recommended in the owner’s

manual of the vehicle, tires should be at their proper inflation level, the brake pads

should be checked regularly, etc. While driving, you should sit comfortably, so that your

hips are back in the seat and your knees are bent, even while braking. Your foot should

be positioned so that your heel is on the floor and your toes are secure on the lower half

of the pedal. And, though ABS may reduce stopping distance, remember: The faster you

go, the longer it takes you to stop. Keeping a safe distance between you and the

vehicle in front of you is always necessary, even with ABS.

What happens if ABS becomes inactive?

The ABS electronic control unit has on-board diagnostic capability. If a fault is detected,

the vehicle will revert to the base brake system, and the ABS telltale on the dash will be

illuminated. Should this happen, the vehicle should be taken to a dealership for repair

as soon as possible.

How do I use ABS?

Depress and hold the pedal. DO NOT PUMP THE BRAKES (that prevents the system from

working). Just hold the brake pedal down and let the ABS work for you. You may feel

the brake pedal vibrate, or you may notice some noise, but this is normal as the system

works for you.

Should I drive an ABS equipped vehicle differently than

I would drive a vehicle with conventional brakes?

Most of the time, under normal driving circumstances, there is no difference,

and you should always drive with the same caution and care. It is important to realize

that ABS only makes a difference when it is activated—when you have

to brake hard—and that would only be when the computer senses that a wheel is

approaching lock up. When ABS activates keep steady pressure on the brake pedal and

then let the ABS work for you. Don’t pump the brakes or try to find the threshold.

Simply hold the brake pedal down and steer if necessary to avoid an obstacle.

Is ABS always active?

ABS is always available, but not always activated. ABS is activated only when the brake

pedal is applied and the computer detects an impending wheel lock condition.

Can older cars be retrofitted with ABS?

No! The brake system is one of the most important features on any passenger vehicle.

Several products, which tap into the master cylinder and/or brake system performance,

are being sold in the aftermarket. Some of these products imply performance similar to

new vehicle anti-lock brake systems.

However, contrary to their claims, add-on systems, which deplete fluid from the master

cylinder on brake apply may actually increase a vehicle’s stopping distance. This may

cause the vehicle to fail to comply with Federal brake standards.

Does ABS always activate at the same speed?

No, the system operates when the computer detects wheel lockup, at any speed above

8 mph.

Will ABS wear out a vehicle’s brakes sooner?

A properly maintained brake system will be unaffected by ABS operation under typical

driving conditions.

Are there different types of ABS?

Yes, there are rear wheel anti-lock systems (RWAL) used on some trucks and four-wheel

ABS available on cars and trucks.

Do Federal Safety Standards mandate ABS?

No. Federal standards establish minimum braking performance requirements that all

vehicles must meet, but do not specify how they should be met. It should be noted that

even a vehicle with failed ABS meets the Federal safety standard for stopping distances.

Will a tire size change affect ABS?

Use of tires other than original equipment may affect ABS performance. Owners should

consult and follow the recommendations contained in the vehicle owner’s manual

regarding replacement tire size.

Note: ABS will work with original equipment spare tire or tire

chains. However, performance is reduced.

Do insurance companies give a discount for ABS?

Yes, many insurance companies give discounts that range from 5% to 10%. In the

states of New York and Florida all insurance companies are required to give an ABS

discount of 5% on certain coverages such as bodily injury, property damage, collision,

and personal injury protection. In other states the discount varies from insurance

company to insurance company. When buying auto insurance, always ask your

insurance agent if his/her company gives a discount for vehicles equipped with anti-

lock brakes.

Note: All dimensions are approximate and subject to change.

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