2009-2017 Audi A4 Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

Every 2009-2017 Audi A4 calls for brake fluid that meets Volkswagen specification VW 501 14, a low-viscosity DOT 4 fluid. If that exact fluid is not on hand, the owner's manual allows a high-grade equivalent that meets FMVSS 116 DOT 4, Class 6. Audi's maintenance schedule for these years says to replace the fluid every 2 years regardless of mileage.

What Brake Fluid Does a 2009-2017 Audi A4 Use?

The A4 owner's manual is specific: the fluid must meet the Volkswagen standard VW 501 14. Audi and VW genuine fluid is sold under the B 000 750 part number family, and several aftermarket fluids are built to the same spec. When the genuine fluid is not available, Audi permits another high-grade brake fluid of equivalent quality, provided it meets U.S. Federal Motor Vehicle Safety Standard 116 DOT 4, Class 6.

That Class 6 part matters. A plain DOT 4 bottle meets the federal boiling-point minimums, but VW 501 14 and ISO 4925 Class 6 fluids are also formulated to stay much thinner in extreme cold. Low cold viscosity lets the ABS and ESC (stability control) hydraulic unit move fluid quickly through its small valves, which is exactly the work those systems do during a panic stop on a frozen road. Pentosin's data sheet for its DOT 4 LV fluid, for example, describes it as ideal for modern vehicles with ESP and ABS and lists the Audi/VW B 000 750 fluids among the OE references it covers.

The table shows why Audi does not simply say "DOT 4." A Class 6 fluid beats the DOT 4 minimums on boiling point and is less than half as thick at minus 40. Do not put DOT 3 in an A4: it has the lowest boiling point targets of the three. Never use DOT 5 silicone fluid either; it is a different chemistry from the glycol fluid the system is filled with.

How Often to Flush the Brake Fluid

Audi's scheduled maintenance for these model years lists a brake fluid replacement every 2 years regardless of mileage. The interval is based on time, not miles, because glycol brake fluid is hygroscopic: it pulls moisture out of the air through the reservoir vent and the rubber hoses whether the car is driven or parked. A low-mileage A4 that sits in a garage still needs the flush on schedule.

Water lowers the boiling point. The federal standard spells this out with two ratings: the dry boiling point of fresh fluid and the wet boiling point after the fluid has absorbed moisture. For DOT 4 the required minimum drops from 230 C dry to 155 C wet. Under hard, repeated braking (a long mountain descent, towing, or track use) the calipers heat the fluid, and if any of it boils, vapor bubbles form. Vapor compresses where liquid does not, so the pedal goes soft or sinks. The A4 manual warns about exactly this: old fluid can form bubbles during heavy braking and reduce braking performance. Moisture also corrodes the inside of calipers, lines and the ABS unit over time.

Checking the Level and What a Drop Means

The brake fluid reservoir sits under a cover on the driver's side of the engine compartment. The level must stay between the MIN and MAX marks. If it falls too low, the instrument cluster shows a warning to stop the vehicle and check the brake fluid level.

• Slow, small drop over months: normal. As the pads wear, the caliper pistons sit farther out and hold more fluid, so the reservoir level falls a little. That is the signal to inspect the pads, not to top off right away. If you top off to MAX on worn pads, the reservoir can overflow when new, thicker pads push the pistons back.
• Fast drop or wet spots: a leak. Check each wheel for wetness at the caliper and hose, and look at the back of the master cylinder.
• Dark, murky fluid: it is past due. Fresh fluid is clear to amber.
• Soft or sinking pedal after hard braking: a classic sign of moisture-laden fluid boiling. Flush it before driving that way again.

Keep brake fluid off the paint. The manual notes it damages the finish on contact, so wipe any spill immediately and rinse with water. It is also poisonous, so store it sealed and away from children.

Doing the Flush on an A4

A flush replaces all the old fluid in the lines and calipers, not just what is in the reservoir. The usual approach is a pressure bleeder on the reservoir, then opening each bleeder screw in the order given in the factory service information until clean fluid comes out, never letting the reservoir run dry. Letting it run dry can pull air into the ABS/ESC hydraulic unit, which may then need a scan-tool bleed routine to clear.

Practical points for a home mechanic:

• Use a sealed, fresh bottle of VW 501 14 or DOT 4 Class 6 fluid. An opened bottle that has sat on a shelf has already started absorbing moisture.
• Tighten bleeder screws to the value in the factory service manual. They are small and easy to strip.
• Pump the pedal to a firm feel before moving the car, and confirm the level sits between MIN and MAX.
• If the pedal is still soft after a full flush, suspect air trapped in the ABS unit or a failing master cylinder, not the fluid.

Audi recommends having brake fluid service done by an authorized facility, and many owners choose a shop for this job because of the ABS unit. With a pressure bleeder it is a straightforward job; with only a helper pumping the pedal it is slower and easier to get wrong.

What to Replace at the Same Time

A fluid flush is a good time to look at everything else in the hydraulic system, since the wheels are already off.

• Pads and rotors: if the reservoir has dropped from pad wear, measure the pads now. Front pads such as the Bosch front ceramic brake pads for the 2009-2017 Audi A4, A5 and Q5 are a common pairing with a flush. Browse more ceramic brake pads and brake rotors.
• Brake hoses: cracked or swollen rubber hoses let in moisture and make the pedal spongy. See our brake hoses.
• Calipers: a sticking piston or a weeping seal often shows up during bleeding. Replacements are in brake calipers.
• Hardware: new clips and slide pin boots with a pad job; see brake hardware kits.

Frequently Asked Questions

Can I use regular DOT 4 in my Audi A4?

Audi's first choice is fluid meeting VW 501 14. If that is not available, the manual allows a high-grade equivalent that meets FMVSS 116 DOT 4, Class 6. A basic DOT 4 without the Class 6 low-viscosity rating does not meet that requirement.

How often should I change the brake fluid on a 2009-2017 A4?

Every 2 years regardless of mileage, per Audi's maintenance schedule. The fluid absorbs moisture with time, not miles.

Can I mix DOT 4 LV with the fluid already in the car?

Glycol-based DOT 3, DOT 4 and DOT 4 LV fluids are chemically compatible, but mixing dilutes the better fluid's performance. Do a full flush with the correct fluid rather than topping off with something different. Never add DOT 5 silicone fluid.

Where is the brake fluid reservoir on an A4?

In the engine compartment on the driver's side, under a cover. The level should sit between the MIN and MAX marks.

Why is my brake fluid level low but there is no leak?

Pad wear. As the pads get thinner, the caliper pistons extend and the reservoir level falls slightly. Check pad thickness before adding fluid.

Sources

1. Audi A4 owner's manual - Brake fluid, checking and filling - VW 501 14 requirement, FMVSS 116 DOT 4 Class 6 alternative, reservoir location, MIN/MAX, warning message, bubble and paint cautions
2. Audi Maintenance for Model Years 2010-2013 - brake fluid replacement every 2 years regardless of mileage
3. 49 CFR 571.116 - FMVSS No. 116, Motor vehicle brake fluids - DOT 3 and DOT 4 dry and wet boiling point minimums and -40 C viscosity limits
4. Pentosin DOT 4 LV product data sheet - boiling points, -40 C viscosity, ISO 4925 Class 6, Audi/VW B 000 750 references, ESP and ABS suitability
5. Ravenol - VW 501 14 approvals - VW 501 14 fluid conforming to ISO 4925 Class 6 and FMVSS 116
6. Audi A4 owner's manual - Brake fluid - level drop from pad wear is normal, brake fluid is poisonous and damages paint