AUTOOL AS502 Brake Fluid Water-Content Tester
US$30.00
- DOT3 / DOT4 / DOT5.1
- Normal + Expert Modes
- 260 mm Flexible Probe
- Water + Status Display
- DOT3 / DOT4 / DOT5.1: Screen water content in supported DOT3, DOT4, and DOT5.1 brake fluids.
- Normal + Expert Modes: Use standard fluid-type testing or select Expert mode for supported DOT4 brand references.
- 260 mm Flexible Probe: Reach brake-fluid reservoirs with the flexible gooseneck probe.
- Water + Status Display: View water content with OK, warning, or suggested-replacement indicators on the 2.8-inch backlit screen.
- DOT3 / DOT4 / DOT5.1: Screen water content in supported DOT3, DOT4, and DOT5.1 brake fluids.
- Normal + Expert Modes: Use standard fluid-type testing or select Expert mode for supported DOT4 brand references.
- 260 mm Flexible Probe: Reach brake-fluid reservoirs with the flexible gooseneck probe.
- Water + Status Display: View water content with OK, warning, or suggested-replacement indicators on the 2.8-inch backlit screen.
- 3-Year Warranty Main unit 3 years · Accessories 1 year
- 90-Day Returns Eligible returns within 90 days
- Official Store Genuine products · Direct support
AUTOOL AS502 · Brake Fluid Water-Content Tester
Match the Fluid Mode Before Screening Moisture
Screen water content in supported DOT3, DOT4, and DOT5.1 brake fluids after matching the fluid mode. AS502 offers a standard test path plus Expert references for supported DOT4 brands, while the flexible reservoir probe and backlit display keep sampling and status review together. Use the result with the vehicle’s service criteria.
- DOT 3 / 4 / 5.1 Modes
- Standard And Expert Paths
- 260 mm Flexible Probe
- 2.8-Inch Backlit Display
- 4 × AAA Battery Power
Key Features
Normal and Expert Brake Fluid Modes
Water-Content Screening
The flexible reservoir probe screens brake-fluid water content in the selected supported mode. It does not generate or measure hydraulic brake pressure.
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.
Single-Handed Control
The silicone grip and handheld control layout support single-handed brake fluid testing.
AAA Battery Power
The tester uses 6V power from 4 × 1.5V AAA batteries. Install batteries with the correct polarity before operation.
Water Content And Status
The screen displays brake fluid water content together with OK, warning and suggested replacement indicators.
5-Minute Auto Power-Off
The tester automatically powers off after 5 minutes without operation to conserve battery power.
3 Years Warranty Support
Main unit: 3-year warranty. Standard accessories: 1-year warranty. Warranty Policy.
Service Workflow
Select, Immerse, Read and Clean
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.
Guided Fluid Check
Clean the probe, select the correct brake fluid type, immerse the probe and start the test. Read the water content percentage and status on the screen.
Safe Use
Separate Fluid Fit from Service Verdict
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.
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.
Routine Check Suggestion
For routine maintenance, checking brake fluid around every 40,000 km is recommended, depending on vehicle condition and service requirements.
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.
Use the Moisture Screening Result
Select the exact brake-fluid mode, clean the probe between samples and use the displayed moisture/grade value for quick fluid screening. It is not a standardized wet boiling-point result.
Model Comparison
Choose the Right Fluid Test Method
Model Guide
Choose one or more models. AS502 is selected by default.
| Product name | AS501 Brake Fluid Tester | AS502 Brake Fluid Tester | AS503 Engine Oil Quality Tester | AS505 Transmission Fluid Tester | AS506 Brake Fluid Boiling Point Tester | AS507 Power Steering Fluid Tester | AS509 Coolant Boiling Point Tester |
|---|---|---|---|---|---|---|---|
| Test Method & Application | |||||||
| Detection Technology | Pressure Boost Detection Technology |
Water-content screening; no hydraulic pressure generation or measurement |
Optical Probe Technology |
Optical Probe Technology |
Sample Heating Technology |
Optical Probe Technology |
Sample Heating Technology |
| Operating Principle | Brake Fluid (Water Content) |
Brake Fluid (Water Content) |
Engine Oil (Transmittance) |
Transmission Fluid(Transmittance) |
Brake Fluid (Boiling Point) |
Steering Fluid (Transmittance) |
Coolant |
| Test Mode Selection | Normal Mode |
Normal Mode/Expert Mode |
Gasoline Engine/Diesel Engine |
Automotive Transmission Fluid |
Normal Mode/Brand Mode |
Automotive Steering Gear |
Normal Mode/Brand Mode |
| Boiling Point Reference Value | × |
× |
× |
× |
✓ |
× |
✓ |
| Normal Mode | 6 Types ENV-4、ENV-6 DOT3、DOT4、DOT5、DOT5.1 |
3 Types DOT3、DOT4、DOT5.1 |
× |
× |
DOT3, DOT4 and DOT5.1 (procedure-confirmed selections) |
× |
23 Coolant Brands For ACDELCO、BASF、BOSCH、CASTROL、ENGINE_ICE、EVANS、FORD、HONDA、JOHN_DEERE、KUNLUN、MOBIL、MOPAR、NISSAN、OMTECH、PEAK、PRESTONE、RECOCHEM、SHELL、SKI-DOO、ZEREX、STAR_BRITE、TOTAL、TOYOTA |
| Measurement & Response | |||||||
| Temperature Unit Switching | × |
× |
℃/℉ |
℃/℉ |
℃/℉ |
℃/℉ |
℃/℉ |
| Temperature Measurement Range | × |
× |
0-85℃ 0-185℉ |
0-85℃ 0-185℉ |
0-320℃ 0-608℉ |
0-85℃ 0-185℉ |
Diluted Coolant Boiling Point Range： 100°C~120°C(212°F~248°F) Original Manufacturer Coolant Boiling Point Reference Range 106°C~191°C(221°F~376°F) |
| Test Duration | 10s Response |
10s Response |
10s Response |
10s Response |
16s Response |
10s Response |
20~40s Response |
| Display, Probe & Power | |||||||
| Backlit Display Screen | 1.8-inch |
2.8-inch |
2.8-inch |
2.8-inch |
1.54-inch |
2.8-inch |
1.6-inch |
| Test Cable Length | 26cm |
26cm |
80cm |
80cm |
4cm |
80cm |
130cm |
| Power Supply Voltage | 3V |
6V |
6V |
6V |
12V |
6V |
10-14V |
| Hose Material | Iron Oxide |
304 Stainless Steel |
Teflon |
Teflon |
× |
Teflon |
× |
Manual & Support
Find the Manual and Fluid-Test Guidance
AUTOOL AS502 User Manual
Open the PDF manual for AUTOOL AS502 brake-fluid selection, normal and expert modes, water-content screening, result interpretation, probe cleaning, safety and troubleshooting support.
Package Contents
See What Comes in the Box
- Main UnitAUTOOL AS502 brake fluid tester with flexible probe
- Retail BoxAS502 product packaging
- ItemUser Manual AS502 user manual
- Battery The tester uses 4 × 1.5V AAA batteries. Confirm whether batteries are included with your selected package before ordering.
Buyer Questions
Fluid Fit, Method and Result Questions
What Does AUTOOL AS502 Test?
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.
Which Brake Fluid Types Does AS502 Support?
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.
What Batteries Does AS502 Use?
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.
How Do I Use AS502 For A Brake Fluid Test?
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.
How Should I Read The Test Result?
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.
How Often Should Brake Fluid Be Tested?
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.
How Should I Maintain The Probe After Use?
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.
What Is The Difference Between AS502 And Other AUTOOL Fluid Testers?
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.
How Long Is The Warranty?
Main unit: 3-year warranty. Standard accessories: 1-year warranty. Warranty Policy.
Jonah Hofmann ✓ Verified Purchase –
The AS502 perfectly meets my needs.
The AS502 perfectly meets my needs. My car has recently been experiencing issues with insufficient brake pressure and soft brakes. After searching online, everyone gave me advice on whether I need to replace the brake fluid. This device tests the water content in the brake fluid to determine whether my car’s brake fluid needs to be replaced. It’s easy to operate and suitable for novices.
Vladyslav ✓ Verified Purchase –
I am very satisfied with the AUTOOL AS502 I purchased.
I am very satisfied with the AUTOOL AS502 I purchased. The device is compact and easy to operate. It can determine whether the brake fluid needs to be replaced by testing the water content of the brake fluid. It is a very practical product.
Cole ✓ Verified Purchase –
This brake fluid tester determines whether the car's brake head needs to be…
This brake fluid tester determines whether the car’s brake head needs to be replaced by detecting the water content of the brake fluid. When used with a brake fluid replacement machine, the number of times the brake fluid needs to be replaced is much faster.