AUTOOL AS502 Digital Brake Fluid Moisture Tester
The AUTOOL AS502 is a professional automotive testing instrument designed to measure the percentage of water present in brake fluid. It helps technicians and vehicle owners evaluate fluid condition and determine whether inspection, maintenance or replacement may be required.
Unlike basic LED testing pens that provide only a general indication, the AS502 displays the measured water-content percentage and fluid status directly on its 2.8-inch backlit screen.
Main Features
• Measures brake fluid water-content percentage
• Supports DOT3, DOT4 and DOT5.1 brake fluids
• Normal and Expert testing modes
• 2.8-inch backlit LCD display
• Approximately 10-second response time
• 260mm flexible testing probe
• Corrosion-resistant stainless-steel probe hose
• Displays OK, warning and replacement indications
• Automatic warning when moisture exceeds the safe range
• Automatic power-off after five minutes of inactivity
• Compact and portable design
• Suitable for professional workshops and personal maintenance
High-Precision Moisture Testing
The AS502 uses electrochemical sensing and digital processing technology to measure changes in brake-fluid conductivity caused by absorbed moisture. The result is displayed as a percentage, providing a clearer assessment than conventional color-indicator testing pens.
Supported Brake Fluids
Normal Mode supports:
• DOT3
• DOT4
• DOT5.1
Expert Mode provides dedicated selections for supported DOT4 fluid brands, including:
• MOTUL
• ATE
• FERODO
• MOBIL
• BREMBO
• TRW
• BOSCH
• CASTROL
• TOTAL
• VALEO
• FUCHS
• TEXTAR
Expert Mode is not universal for every brake-fluid manufacturer. Always select the option that matches the fluid being tested.
Clear Digital Results
The backlit screen displays the measured water-content percentage together with an easy-to-understand condition indicator:
• OK: Brake fluid condition is acceptable
• Warning symbol: Moisture level requires attention
• Replacement symbol: Brake-fluid replacement is suggested
General Result Interpretation
• 0%–2%: Acceptable range
• 2%–3%: Warning range; monitor or service the fluid
• Above 3%: Replacement is generally recommended
Always follow the vehicle manufacturer’s maintenance specifications when making the final service decision.
Flexible Stainless-Steel Probe
The 260mm flexible probe provides convenient access to brake-fluid reservoirs in different engine compartments. Its stainless-steel outer hose offers resistance to oxidation, oil and corrosion.
Fast Testing
The AS502 provides a measurement in approximately 10 seconds, making it suitable for quick vehicle inspections, workshop maintenance and pre-service brake-system checks.
How to Use
- Install four 1.5V AAA batteries with the correct polarity.
- Press and hold the power button to turn on the tester.
- Clean and dry the metal testing probe.
- Carefully open the vehicle’s brake-fluid reservoir.
- Select the correct brake-fluid type or supported Expert Mode brand.
- Immerse the probe in the brake fluid.
- Press the test button and wait for the displayed result.
- Read the moisture percentage and condition indicator.
- Clean the probe thoroughly after testing.
Technical Specifications
• Model: AUTOOL AS502
• Testing function: Brake-fluid water-content measurement
• Supported fluids: DOT3, DOT4 and DOT5.1
• Testing modes: Normal Mode and Expert Mode
• Display: 2.8-inch backlit LCD
• Response time: Approximately 10 seconds
• Probe length: 260mm
• Probe hose material: 304 stainless-steel outer hose
• Operating voltage: 6V
• Power supply: 4 × 1.5V AAA batteries
• Operating temperature: -10°C to 60°C
• Automatic shutdown: After approximately five minutes
• Main-unit dimensions: Approximately 175 × 72 × 29mm
Package Contents
• 1 × AUTOOL AS502 Brake Fluid Tester
• 1 × User Manual
• 1 × Retail Package
Batteries may not be included. Confirm the supplied package before purchasing.
Important Notes
The AS502 is designed specifically for measuring moisture in supported brake fluids. It does not test engine oil, transmission fluid, power-steering fluid or coolant.
DOT5 silicone-based brake fluid is different from DOT5.1 and is not listed as supported by this model.
Clean the probe before and after every test. Residue from a previous sample may affect the accuracy of later measurements. Brake fluid can damage painted surfaces, so handle it carefully and immediately clean any spills.
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