Disc brake diagnosis

Disc brake diagnosis is important to vehicle safety, but it’s also important for the drive ability of the vehicle. Car owners often complain about their automobiles braking system. In particular about the way the brakes sound or how they feel when the pedal is pushed with the foot. However, they might put off repair of these complaints if the vehicle stops well and they feel safe.

On the other hand when a brake warning light comes on most drivers will seek out diagnosis immediately. Or at least they should. Driving around with a red or amber colored warning light on isn’t a good idea. Below are a few reasons why these dash lights may come on and other symptoms associated with specific problems.

Brake Warning Lights

Break Warning Light
Break Warning Light

Sometimes a brake warning light will appear on the dash even though the brakes feel fine to the driver. A complete inspection of the brake system including rotors, calipers, and pads should be performed before road testing the vehicle to confirm the complaint.

In this article we will discuss the 2 types of brake warning lights. These can be common complaints that may require careful diagnosis. The importance of getting the correct diagnosis on the first attempt is amplified by the safety ramifications of this critical automotive system.


Modern vehicles are normally equipped with more than one brake warning light on the instrument panel. Regardless of what warning light is lit, it is an indication or warning to the driver that a problem exists. A basic understanding of what would cause the different lights to illuminate is necessary to diagnose the problem properly.

The red brake warning light indicates there is a problem in the regular braking system. Low brake fluid levels as well as the parking brake being applied will illuminate this light. When ever low brake fluid level is the cause of your red brake warning light. You should suspect a leak or very worn brake pads. A red brake warning light is a serious alert to both the mechanic and the driver. If you find low fluid level, along with worn brake pads take the extra time to inspect the vehicle for a brake fluid leak.

ABS Warning Light

PictureThe yellow or the Amber brake warning light that is usually marked ABS is tied into the antilock brake system. This light turns on for two reasons.

The first reason would be to notify the driver of a recorded problem in the system. The antilock brake system performs a system test on every key cycle.


This is a self-test and is usually conducted by a separate brake control computer. Any failures during the self-test are recorded as a code and points to the particular system with the malfunction.

The best way to approach diagnosis of this system is to pull the codes and follow a diagnostic tree chart for the particular brake problem.

The good old equus 3150 auto scan tool performs both obd II and ABS code reading functions in one tool.

ABS system Normal Operation

Also note that the ABS warning light on most models will turn on when the ABS system becomes active. This is a normal condition and shows the proper function of the ABS. An example would be if you jam on the brakes during a panic stop on a wet slippery day.

A brake pedal might pulsate and you’re ABS light may come on to show active braking functions. A driver who has never experienced these conditions might generate a complaint of a problem that is actually normal. If the light does not go out after the ABS becomes active. Then there is a problem that needs to be diagnosed in the brake system.

You can see my latest related post about brake pad diagnosis. You can also learn more about what other kinds of Diy auto repair information is available on the home page for online auto repair. For an overview of how to approach automotive diagnostics visit my basic auto repair diagnostic tips page.