AUTOOL Brake Fluid Moisture Tester AS501 — Digital Brake Fluid Tester, 1.8" HD Display & Stainless Probe

AUTOOL AS501 is a handheld digital brake fluid moisture tester that quickly measures water content in DOT brake fluids to help determine when fluid replacement or service is needed.

The AUTOOL AS501 combines a bright 1.8-inch HD backlit LCD with a stainless steel probe and boosted conductivity sensing to deliver fast, repeatable readings for DOT 3, DOT 4, DOT 5, DOT 5.1, ENV-4 and ENV-6 fluids. Lightweight and battery powered, it’s built to live in a technician’s toolbox or a home mechanic’s glovebox so you can verify brake fluid condition in roughly 10 seconds without guesswork.

How does the AS501 detect moisture in brake fluid?

The AS501 uses high-sensitivity conductivity analysis: water changes a fluid’s electrical conductivity, and the tester translates that change into a moisture reading on the display. Its stainless steel probe ensures consistent contact with fluid while resisting corrosion from brake compounds.

• Conductivity-based sensor for reliable water detection
• Stainless steel probe resists corrosion for longer life
• Typical reading time of about 10 seconds per test
• Clear numeric results shown on a 1.8" HD backlit LCD

Which brake fluids and vehicles are compatible with this tester?

Designed to work with a wide range of common automotive brake fluids, the AS501 supports DOT 3, DOT 4, DOT 5, DOT 5.1 and newer environmental formulas like ENV-4 and ENV-6. That broad compatibility makes it suitable for most passenger cars, motorcycles, and light trucks encountered in routine maintenance.

• Tests DOT 3, DOT 4, DOT 5, DOT 5.1 fluids and ENV-4/ENV-6
• Works for cars, motorcycles, light trucks and fleet vehicles
• Portable for roadside or shop use — battery powered
• Useful for pre-purchase checks and routine inspections

How easy is it to use and read results on the AS501?

Operation is straightforward: power on, insert the probe into a brake fluid sample, and wait for the display to show the moisture percentage or status. The 1.8-inch HD backlit LCD ensures results are readable in bright daylight or low-light conditions, reducing interpretation errors for both pros and DIYers.

• Simple one-hand operation for quick tests
• Backlit LCD for easy viewing in any light
• Battery powered by two AA cells for portability
• Fast warm-up and immediate results in about 10 seconds

What durability and support features does the AUTOOL AS501 offer?

The AS501 is built with a corrosion-resistant stainless steel flexible probe to withstand repeated exposure to brake fluids, and the low-power electronics extend battery life during field use. Manufacturer support includes a multi-year service period to help maintain long-term reliability.

• Corrosion-resistant stainless steel probe for longevity
• Low power consumption — runs on two AA batteries
• Fast, repeatable readings reduce diagnostic time
• Backed by a three-year service and technical support plan

Who this is for: The AUTOOL AS501 is intended for automotive technicians, fleet managers, motorcycle mechanics and knowledgeable DIYers who want a quick, affordable way to assess brake fluid condition without lab equipment. If you regularly inspect braking systems or perform fluid maintenance, the AS501 provides a compact, reliable tool to help prioritize service and maintain consistent braking performance.