Audi A4 B7: Brakes Diagnostics Guide

This article applies to the Audi A4 B7 (2005-2009).

There are various things that can go wrong with your Audi A4's brake system that could affect its stopping power. Whether you hear noises when you brake, your brake pedal feels spongy, or you feel like your Audi doesn't stop as well as it usually does, this guide will help you get to the bottom of the problem. It's highly recommended that you don't drive your Audi when you feel something is wrong with the brakes. Read on to learn how to diagnose your brake system.

Step 1 – Check master cylinder

You could be low on fluid.

If you're low on fluid, then you may be facing a brake leak. Check the master cylinder for proper fluid level. If it's too low, grab your flashlight and start digging around for a leak. Check around your brake master cylinder for any leaks, then check under your vehicle. Check your brake line connections, between each other and between the lines as well as the calipers. If you find a leaking brake line, replace it and bleed the brake system. A leaking brake line will usually affect the brake performance, as well as the brake pedal; it will feel spongy.

If the fluid level is proper, proceed to Step 2.

Step 2 – Check brake pads

They could be worn.

The brake pads should be replaced as part of the maintenance intervals. The pads should be replaced on average every 50,000 miles. However, if you're heavy on the brake pedal, you could need to replace them before then. Worn brake pads are usually accompanied with squealing noise when stepping on the brake pedal. If you don't change the brake pads when they are worn, they will wear your brake rotors as well, which will then cost you a lot more. Loosen the lug nuts on the wheel where the noise is coming from, raise your car, then secure it with jack stands. Remove the wheel, then remove the two bolts on the back of the brake caliper using your socket. Remove the brake caliper up and off the rotor, then place it somewhere where it doesn't hang from the brake line. Visually inspect the brake pads. The minimum legal thickness for brake pads are 2-3mm in thickness. If it's thinner, replace the pads as a set.

(Related Article: How to Replace Brake Pads/Calipers/Rotors - AudiWorld)

If the brake pads are not too thin, proceed to Step 3.

Step 3 – Check brake rotor

It could be grooved, cracked, or rusted.

The brake rotor can go bad if you don't replace the brake pads on time, or if you live in an area with rough weather conditions where they can rust out. With the wheel removed, visually inspect the rotor. Look for any cracks, rust, or grooves. The rotor should be smooth and clean. If you find out you need new brake rotors, you can remove them by pulling them straight out. If they are stuck in there, use a rubber mallet and tap the center of the rotor, and when it comes loose, pull it straight out.

If the rotor is in a good condition, proceed to Step 4.

Step 4 – Check brake caliper

Its pistons could be stuck.

Stuck or seized pistons could hurt your brake pads and rotors. If you feel resistant in the way the car drives, you hear consistent squealing noise, or if you smell a burning smell, this is your pads rubbing on your rotor, even without you stepping on the brake pedal. Check the brake caliper, and even though the calipers can often live for as long as the vehicle does, your calipers can go bad. If your pistons are stuck, replace the calipers as soon as you can to avoid any further damage to the pads and rotors. You will need to bleed the brake system after replacing the caliper.

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