The AUTOOL AS502 is a handheld brake fluid tester for checking the water content percentage in DOT3, DOT4, and DOT5.1 brake fluid. It combines pressure boost detection, normal and expert test modes, a 260mm flexible probe, and a 2.8-inch backlit LCD screen to help users judge brake fluid condition before replacement.
Review the brake-fluid type, battery, test interval, probe cleaning, and storage notes before using the AS502 brake fluid tester.
Brake Fluid Water Test
AS502 is designed to test the water content percentage in brake fluid. It is not an engine oil, transmission fluid, or power steering fluid tester.
Routine Check Suggestion
For routine maintenance, checking brake fluid around every 40,000 km is recommended, depending on vehicle condition and service requirements.
Use Supported Fluids Only
Use AS502 with supported brake fluid types. Normal mode is for DOT3, DOT4, and DOT5.1 brake fluid; expert mode is for selected DOT4 brands.
Install 4 AAA Batteries
The tester uses 6V power from 4 × 1.5V AAA batteries. Install batteries with the correct polarity before operation.
Clean The Probe
Wipe the probe clean before each measurement and clean it after use to avoid fluid residue affecting later tests.
Store Dry
If the tester will not be used for a long time, remove all batteries and store the unit in a dry place at normal room temperature.
Key Features
Key Features
AS502 focuses on fast brake fluid water-content testing with pressure boost detection, two test modes, a flexible stainless-steel probe, comfortable handheld control, and a readable backlit screen.
Pressure Boost Detection
Pressure boost detection technology helps improve test stability and supports clearer brake fluid water-content measurement.
Multiple Brake Fluid Support
Normal mode supports DOT3, DOT4, and DOT5.1 brake fluid, making AS502 suitable for common vehicle brake fluid checks.
Normal And Expert Modes
Switch between standard brake-fluid type testing and expert mode for selected DOT4 brands when more targeted fluid selection is needed.
260mm Flexible Probe
The 260mm gooseneck probe helps reach the brake fluid reservoir more easily during vehicle maintenance.
304 Stainless Steel Outer Hose
The probe hose outer layer uses 304 stainless steel for oil resistance, oxidation resistance, and corrosion resistance.
2.8-inch Backlit Display
The 2.8-inch LCD backlit display makes the result easier to read in bright or low-light working conditions.
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Compatibility And Fitment
Compatibility And Fitment
AS502 offers two detection modes. Select the correct mode according to the brake fluid type or supported DOT4 brand before testing.
Normal ModeSuitable for DOT3, DOT4, and DOT5.1 brake fluid water-content testing.
Expert ModeSuitable for selected DOT4 brands, including MOTUL, ATE, FERODO, MOBIL, BREMBO, TRW, BOSCH, CASTROL, TOTAL, VALEO, FUCHS, and TEXTAR.
Selection CheckDo not treat expert mode as universal support for every fluid brand. Match the on-screen mode to the fluid being tested.
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Specifications
AUTOOL AS502 Product Specifications
AS502 uses 6V battery power, a 2.8-inch display, 10-second response, pressure boost detection technology, and a 260mm 304 stainless-steel probe hose for brake fluid water-content checks.
Core Specifications
Product
AUTOOL AS502 Brake Fluid Tester
Testing Object
Brake fluid water content percentage
Detection Technology
Pressure boost detection technology
Operating Principle
Brake fluid water-content testing
Supported Brake Fluid
DOT3 / DOT4 / DOT5.1 in normal mode; selected DOT4 brands in expert mode
Display
2.8-inch LCD backlit display
Power Supply
6V, 4 × 1.5V AAA batteries
Test Duration
10-second response
Probe / Test Cable Length
260mm / 26cm
Hose Material
304 stainless steel outer hose
Operating Temperature
-10°C~60°C
Modes
Normal Mode / Expert Mode
Auto Power Off
Automatically powers off after 5 minutes of no activity
Main Unit Size
175 × 72 × 29mm
Warranty
3 years for the main unit; 1 year for included accessories
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Core Specifications
ProductAUTOOL AS502 Brake Fluid Tester
Testing ObjectBrake fluid water content percentage
Supported Brake FluidDOT3 / DOT4 / DOT5.1 in normal mode; selected DOT4 brands in expert mode
Display2.8-inch LCD backlit display
Power Supply6V, 4 × 1.5V AAA batteries
Test Duration10-second response
Probe / Test Cable Length260mm / 26cm
Hose Material304 stainless steel outer hose
Operating Temperature-10°C~60°C
ModesNormal Mode / Expert Mode
Auto Power OffAutomatically powers off after 5 minutes of no activity
Main Unit Size175 × 72 × 29mm
Warranty3 years for the main unit; 1 year for included accessories
How To Use
How To Use
Install batteries, clean the probe, select the correct brake fluid type, immerse the probe, and start the test. The screen displays the water content percentage and replacement status.
Install Batteries
Open the rear battery cover, insert 4 × 1.5V AAA batteries with correct polarity, then close the cover securely.
Power On
Long press the power button for more than 2 seconds to turn on the tester.
Clean The Probe
Wipe the probe clean before each measurement to avoid residue affecting the result.
Open The Reservoir
Open the brake fluid reservoir cap and prepare the brake fluid sample area for testing.
Select Fluid Type
Press the selection button to choose DOT3, DOT4, DOT5.1, or an available expert-mode DOT4 brand.
Immerse And Test
Submerge the probe into the brake fluid, press the test button, and read the displayed water content percentage and status indicator.
Result Reading And Use Notes
% shows the percentage of water content in brake fluid.
OK indicates the brake fluid water content is good.
! indicates a brake fluid water-content warning.
× indicates replacement is suggested.
0%-2% is displayed as a pass range, 2%-3% as a warning range, and above 3% as a replacement range.
The tester automatically powers off after 5 minutes of no activity.
Press and hold the power button for 2 seconds after measurement to turn off the tester.
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Product Comparison
Product Comparison
Compare AS502 with other AUTOOL automotive oil and fluid analyzers before choosing a tester for brake fluid water content, engine oil quality, transmission fluid, boiling point, or power steering fluid.
AS502 FocusBrake fluid water-content testing with pressure boost detection, 2.8-inch backlit display, 6V power, 10-second response, 26cm test cable, and normal/expert mode support.
AS501 DifferenceAS501 also tests brake fluid water content, but uses a 1.8-inch display, 3V power, and iron oxide hose material.
AS503 / AS505AS503 is for engine oil quality by transmittance. AS505 is for automatic transmission fluid testing by transmittance.
AS506 / AS507AS506 tests brake fluid boiling point. AS507 tests power steering fluid by transmittance.
Decision CheckChoose according to the fluid type and test principle, not only by appearance. AS502 is the right choice when the target is brake fluid water content with normal and expert mode selection.
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Related Products
Related Products
Compare related AUTOOL fluid testers for brake fluid water content, engine oil quality, transmission fluid, brake fluid boiling point, and power steering fluid testing.
Select options
This product has multiple variants. The options may be chosen on the product page
Select options
This product has multiple variants. The options may be chosen on the product page
Manual And Downloads
Manual And Downloads
Download the AS502 manual for battery installation, button functions, standard and expert mode selection, operation steps, result reading, maintenance, and warranty information.
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AUTOOL AS502 User Manual
Open the PDF manual for setup, brake-fluid type selection, result interpretation, probe maintenance, and warranty details.
Contact AUTOOL Store before ordering or testing if you need help confirming battery setup, DOT3 / DOT4 / DOT5.1 compatibility, normal or expert mode selection, result reading, or fluid tester model choice.
The packing list image shows the AS502 brake fluid tester, retail box, and user manual. Final package contents should follow the actual product option and package received.
Main UnitAUTOOL AS502 brake fluid tester with flexible probe
Retail BoxAS502 product packaging shown in the package image
User ManualAS502 user manual shown in the package image
Battery NoteThe tester uses 4 × 1.5V AAA batteries. Batteries are not shown in the package image; confirm the actual package option before ordering if needed.
Questions And Answers
These answers cover AS502 testing purpose, supported brake fluids, batteries, operation, result reading, maintenance, comparison, and warranty support.
AUTOOL AS502 tests the water content percentage in brake fluid. It helps users evaluate brake fluid condition and decide whether maintenance or replacement may be needed.
Normal mode supports DOT3, DOT4, and DOT5.1 brake fluid. Expert mode supports selected DOT4 brands, including MOTUL, ATE, FERODO, MOBIL, BREMBO, TRW, BOSCH, CASTROL, TOTAL, VALEO, FUCHS, and TEXTAR.
AS502 uses 6V power from 4 × 1.5V AAA batteries. Open the rear battery cover, insert the batteries with the correct polarity, and close the cover securely before use.
Clean the probe, open the brake fluid reservoir cap, select the correct brake fluid type or expert-mode brand, immerse the probe into the brake fluid, then press the test button. The screen will display the water content percentage and status indication.
The percentage value shows the water content in the brake fluid. OK indicates the water content is good, ! indicates a warning, and × indicates replacement is suggested. The manual describes 0%-2% as a pass range, 2%-3% as a warning range, and above 3% as a replacement range.
For routine maintenance, checking brake fluid around every 40,000 km is recommended. Actual testing frequency should also follow the vehicle condition, driving environment, and service requirements.
Wipe the probe clean after use and avoid leaving stains or brake fluid residue on the probe. If the tester will not be used for a long time, remove all batteries and store it in a dry place at normal room temperature.
AS502 is for brake fluid water-content testing with a 2.8-inch display, 6V power, and normal/expert modes. AS503 is for engine oil quality, AS505 is for transmission fluid, AS506 is for brake fluid boiling point, and AS507 is for power steering fluid. Choose by the fluid type and test principle you need.
From the date of receipt, AUTOOL provides a 3-year warranty for the main unit and a 1-year warranty for included accessories. Warranty handling depends on the actual breakdown situation and warranty conditions.
Warranty And Contact
Warranty And Contact
For AS502 battery setup, brake-fluid compatibility, normal or expert mode selection, result reading, probe maintenance, manual download, package confirmation, warranty support, or model selection, contact AUTOOL Store directly.
Pre-Sales And Product Support
Use support if you need help confirming whether AS502 is suitable for your brake fluid type, how to interpret test results, how to maintain the probe, or which AUTOOL fluid tester fits your workshop needs.
3-year warranty for the AS502 main unit and 1-year warranty for included accessories
DOT3 / DOT4 / DOT5.1 and expert-mode brand confirmation
Battery installation and power setup help
Probe cleaning and long-term storage guidance
Result reading and replacement-status explanation
AS501 / AS502 / AS503 / AS505 / AS506 / AS507 model selection support
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Tamosauskas (verified owner) –
Super
Cheap and great tool, I would recommend it!
Benedict Brown (verified owner) –
AS502 can test the water content in brake fluid!
AS502 can test the water content in brake fluid! It’s a great tool and I always trust AUTOOL’s quality!
Paddy Patience (verified owner) –
It's outstanding.
Being able to accurately determine the water content of my gasoline so I can know how often I can change my oil is a great help in my daily car use!