If you are investigating a hissing sound near the brake pedal, save every stored and pending code before clearing anything. Save engine or brake-system codes if warning lights are present. Record the engine temperature and load alongside the reading; the same value can mean different things in different conditions.
A basic reader may not access every module. Check for a change in brake assist; do not try to repair vacuum components without service information. Use the exact vehicle’s service information to interpret the result.
Quick educational note
For information, not a diagnosis or repair instruction. Vehicle-specific checks are still required. Consult the manufacturer's guidance and a qualified technician.
How to use this information
This article explains general principles and does not establish what is wrong with your vehicle. Read the content limitations.