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Source: https://autoboss.com/product/autool-as502-car-brake-fluid-tester-brake-fluid-moisture-tester/
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Reviews·19

5.0 / 5Based on 19 reviews
4 ★0%
3 ★0%
2 ★0%
1 ★0%
Vladyslav

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.

Boyd N.

First time to use a testing device Feeling good and professional Seller is very…

First time to use a testing device Feeling good and professional Seller is very good Any problem seller will explain one by one

Austin L.

Bought this to stop guessing when my brake fluid needed changing. Just pick the fluid type, dip the probe in, press test — 10 seconds and it shows the water content plus an OK/replace status. Tested it against fresh DOT4 (read ~0%) and old overdue fluid (flagged replace), so the readings look real. Flexible probe reaches the reservoir easily

Specifications

BrandAUTOOL
Weight400 g
Measuring ObjectBrake fluid water content
Applicable FluidsDOT3 / DOT4 / DOT5.1
ModesNormal mode + expert mode (DOT4 brands)
Probe260 mm gooseneck probe, 304 stainless steel outer tube
Response Time10s
Display2.8-inch backlit LCD
Result IndicationWater content %: 0–2% pass, 2–3% warning, >3% replacement recommended
Power Supply4 × 1.5V AAA, 6V; auto power off after 5 minutes
CompatibilityExpert mode DOT4 brands: MOTUL, ATE, FERODO, MOBIL, BREMBO, TRW, BOSCH, CASTROL, TOTAL, VALEO, FUCHS, TEXTAR

Details

Screen Brake Fluid Moisture Straight From the Reservoir

Dip the AS502’s flexible probe into the reservoir and read the water content with an OK, warning or replace indicator. Normal mode covers DOT3, DOT4 and DOT5.1; expert mode adds references for selected DOT4 brands. Brake fluid only.

  • DOT3 / DOT4 / DOT5.1
  • Normal + Expert Modes
  • 260 mm Flexible Probe
  • 2.8-Inch Backlit LCD
  • 4 × AAA Power

Key Features

  1. Water-Content Screening

    Measures the water percentage in brake fluid for quick condition checks. It does not generate or measure hydraulic brake pressure.

  2. Normal and Expert Modes

    Choose a standard fluid type, or switch to expert mode for more targeted selection by DOT4 brand.

  3. Reservoir-Reach Probe

    The gooseneck probe bends into the reservoir; its stainless steel outer layer resists oil, oxidation and corrosion.

  4. Clear Status Indicators

    OK means the water content is good, ! is a warning and × suggests replacement, shown beside the percentage.

  5. Single-Handed Use

    A silicone grip and handheld button layout let you test with one hand.

  6. Battery Saving

    Switches itself off when left idle.

AS502 vs AS501

AS502 AS501
Display 2.8-inch backlit 1.8-inch backlit
Test modes Normal / Expert Normal
Normal-mode fluids DOT3, DOT4, DOT5.1 ENV-4, ENV-6, DOT3, DOT4, DOT5, DOT5.1
Power supply 6 V 3 V
Probe hose material 304 stainless steel Iron oxide

What’s in the Box

  • AS502 brake fluid tester with flexible probe
  • User manual
AUTOOL AS502 brake fluid tester with its retail box and user manual
AS502 tester, retail box and user manual.

How to Use

  1. Install batteriesOpen the rear cover, insert four AAA batteries with correct polarity and close the cover securely.
  2. Power onHold the power button for more than 2 seconds.
  3. Clean the probeWipe the probe before each measurement so residue does not affect the result.
  4. Open the reservoirRemove the brake fluid reservoir cap.
  5. Select the fluidPress the selection button to choose DOT3, DOT4, DOT5.1 or an expert-mode DOT4 brand.
  6. Immerse and testSubmerge the probe, press the test button and read the water percentage and status.

Modes, result interpretation and troubleshooting: AS502 user manual (PDF).

Good to Know

Caution
  • For brake fluid only; it is not an engine oil, transmission fluid or power steering fluid tester.
  • Batteries may not be included; confirm with your package before ordering.
Care
  • The reading is a moisture screening, not a standardized wet boiling-point result; apply it with the vehicle’s service criteria.
  • For routine maintenance, checking brake fluid around every 40,000 km is suggested, depending on vehicle condition.
  • Wipe the probe clean after use and leave no fluid residue on it.
  • For long storage, remove all batteries and keep the tester dry at room temperature.

You may also like

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Offers

  • 10%
    10% off AUTOOL & MRCARTOOLBrands: AUTOOL, MRCARTOOL, FXTUL, CMTOOL, DUOYI · United States, United Kingdom and Australia only. Cannot be combined with other coupons.Code: AB10OFF

Offers are applied at checkout according to the store rules.

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Delivery

Ships in 1-3 business days

Warehouses

  • US Warehouse
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  • UK Warehouse
  • CN Warehouse

Choose the warehouse in the specifications.

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Available methods may vary by currency and billing country; the final list is shown at checkout.

Service

  • Secure checkout

    Payments are processed over an encrypted connection.

  • After-sales support

    Contact us for installation or usage questions.

Specifications

Brand
AUTOOL
Weight
400 g
Measuring Object
Brake fluid water content
Applicable Fluids
DOT3 / DOT4 / DOT5.1
Modes
Normal mode + expert mode (DOT4 brands)
Probe
260 mm gooseneck probe, 304 stainless steel outer tube
Response Time
10s
Display
2.8-inch backlit LCD
Result Indication
Water content %: 0–2% pass, 2–3% warning, >3% replacement recommended
Power Supply
4 × 1.5V AAA, 6V; auto power off after 5 minutes
Compatibility
Expert mode DOT4 brands: MOTUL, ATE, FERODO, MOBIL, BREMBO, TRW, BOSCH, CASTROL, TOTAL, VALEO, FUCHS, TEXTAR

Reviews19

5.0 / 5Based on 19 reviews
4 ★0
3 ★0
2 ★0
1 ★0
Vladyslav

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.

Boyd N.

First time to use a testing device Feeling good and professional Seller is very…

First time to use a testing device Feeling good and professional Seller is very good Any problem seller will explain one by one

Austin L.

Bought this to stop guessing when my brake fluid needed changing. Just pick the fluid type, dip the probe in, press test — 10 seconds and it shows the water content plus an OK/replace status. Tested it against fresh DOT4 (read ~0%) and old overdue fluid (flagged replace), so the readings look real. Flexible probe reaches the reservoir easily

paul

I’m really satisfied with the AS502 Brake Fluid Moisture Tester. It is simple to use and gives stable and reliable test results. The tester helps me easily check brake fluid moisture on vehicles. Fast shipping and good packaging. Worth buying for auto repair work!

Jonah H.

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.

Cole

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.

Hayden M.

The brake fluid test data is very accurate.

The brake fluid test data is very accurate. Since brake fluid absorbs water very easily, I think it is very necessary to purchase this machine. I tested several types of brake fluid and compared the results with old brake fluid. The data is reliable and trustworthy. Furthermore, I understand that AUTOOL obtained this data through extensive repeated experiments, so I have great confidence in this brand.

Chasel Y.

I bought this because I recently bought a used car but I wasn't sure if the…

I bought this because I recently bought a used car but I wasn’t sure if the brake fluid needed to be changed so I ordered this tool and it’s great, I usually do my own maintenance on my car and it was very convenient to use it to do the test and I found out that my brake fluid did need to be changed.

Colin K.

Very impressed with this tester.

Very impressed with this tester. The construction feels solid and reliable, and it even came with batteries included, ready to use right out of the box. Shipping was fast, and the product was neatly packaged. Overall, a great value for the price. Highly recommended!

Alexander

Good

Product description matches. Fast delivery and carefully packaged.

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AUTOOL AS502 Moisture Brake Fluid Tester for DOT3/DOT4/DOT5.1
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AUTOOL AS502 Brake Fluid Moisture Tester
AUTOOL AS502 Moisture Brake Fluid Tester for DOT3/DOT4/DOT5.1

US$30.00

Select options This product has multiple variants. The options may be chosen on the product page