The 1999 BMW 528i is part of the E39 generation of the 5-series, a four-door luxury sedan. The E39 is a very popular car thanks to its appearance, its performance and its high-end German engineering. Like any car, the 5-series should be properly and regularly maintained in order to keep in on the road reliably. If the brake pedal feels spongy and has a longer-than-normal travel, the culprit may by a low brake fluid reservoir. It is easy to fill the reservoir on an E39.
Open the hood. Locate the cabin filter enclosure, which is located on the driver’s side of the engine bay just in front of the windshield.
Unclip the long metal clamp on the air filter housing. Remove the filter from the air duct tube, pulling up and toward the middle of the car. You should see the brake fluid reservoir and the cap for the reservoir once the filter is removed.
Wipe the area around the cap with a rag to keep debris from getting into the reservoir. Unscrew the cap by turning it counterclockwise. Check the level of the brake fluid. If it is low, top it up with DOT4 brake fluid. Reinstall the cap.
Reinstall the cabin filter on the air duct. Install the metal clip on the front. Shut the hood.
