How to Check Brake Fluid: Level and Condition
A level look, a color look and a moisture reading help check brake fluid, and this guide walks through each check with pens and strips that read DOT 3, DOT 4 and DOT 5.1 fluid.
On this page
How to check brake fluid comes down to a level look, a color look and a moisture reading. Park on level ground, open the reservoir cap, look at the level and the color of the fluid, then dip a pen or a strip into the fluid and read what it shows. A reading inside the pen’s stated band, with fluid at the marked level, is the sign the listings describe; a reading above the pen’s stated change band points to the vehicle manual for the next step.
As an Amazon Associate I earn from qualifying purchases. GarageToolHQ earns a commission when you buy through links on our product pages, at no extra cost to you. Read our affiliate disclosure.
KAIWEETS Brake Fluid Tester
A pen with a flexible gooseneck probe, a 3-color LCD, data hold and an audible warning, calibrated to ±0.3% for DOT 3, DOT 4, DOT 5.1, ENV4 and ENV6 fluid.
Pros
- Reads DOT 3, DOT 4, DOT 5.1, ENV4, ENV6
- Flexible gooseneck probe reaches tight reservoirs
- 3-color LCD, data hold, work light, audible warning
- 3-year warranty; batteries and manual included
Cons
- No coolant reading is stated
- No full range stated, only color bands
- Probe needs cleaning after each check
- Auto shut-off after 5 minutes
Xtruck Brake Fluid Tester Pen with Corrosion
A pen with a screen display and a corrosion-resistant probe, reading 0% to 4% moisture with ±0.3% accuracy and an alarm past 3%.
Pros
- Screen shows the moisture reading directly
- Reads 0% to 4% with ±0.3% accuracy
- Alarm sounds when moisture passes 3%
- Corrosion-resistant probe for repeated checks
Cons
- Warranty entry reads '1', no unit, no term counted
- Needs a AAA battery, not included
- No data hold function is stated
- Spec table spells the model 'break' for 'brake'
Phoenix Systems 15-Pack Double-Ended Brake Fluid
A 15-pack of double-ended strips that read brake fluid and coolant condition in 60 to 90 seconds, with a 3 year accuracy guarantee.
Pros
- 15-pack covers many checks
- Reads brake fluid and coolant
- Result in 60 to 90 seconds
- 3 year accuracy guarantee
Cons
- No moisture percentage, only a condition reading
- Spec table says 1 item; title and bullets say 15-pack
- Coolant needs diluting to 50/50 in the vehicle
- Strips only, no pen or reader included
ecocstm 2 PCS Brake Fluid Tester
A 2-pack of pens with 5 LED indicators and a metal probe that reads the water percentage in DOT 3, DOT 4 and DOT 5.1 brake fluid.
Pros
- 2-pack gives a spare pen
- 5 LEDs show the water percentage
- Metal probe dips fully into the fluid
- Frosted plastic housing with anti-slip grip
Cons
- Needs one AAA battery, not included
- No warranty term is stated
- No screen display; LEDs only
- Metal additives may cause the red light to come on
How to Check Brake Fluid: Level and Condition
Start with the reservoir under the hood. Wipe the cap clean before opening it, then read the level against the marks on the reservoir and note the color. If the level sits low, check the vehicle manual before adding fluid.
How to Check Brake Fluid in Order
- Park on level ground. Switch the engine off.
- Wipe the cap clean. Clean the cap before opening it, so dirt stays out.
- Read the level and the color. Read the level against the reservoir marks and note the color.
- Dip the pen or strip. Put the probe or the strip into the fluid as the listing directs.
- Wait for the reading. Strips show the condition in 60 to 90 seconds, while pens show a moisture reading on a display or LEDs.
- Compare the reading with that pen’s own bands in the table below. Check the vehicle manual for the next step.
What the Moisture Bands Mean
The pens state their own bands, and the two listings in the table do not use the same cutoffs. The ecocstm listing states 5 LEDs but no bands, and the Phoenix strips give a condition reading with no bands, so neither is in the table.
| Pen | Reading | What it means |
|---|---|---|
| Xtruck pen | Under 1.5% | Fluid is great |
| Xtruck pen | 1.5% to 3% | Fluid can be used, but needs frequent checks |
| Xtruck pen | Over 3% | Alarm sounds, fluid needs changing |
| KAIWEETS pen | 0 to 2%, green | Fluid is safe |
| KAIWEETS pen | 2 to 3%, orange, slow beep | Replacement soon |
| KAIWEETS pen | Above 3%, red, rapid beep | Immediate action |
Brake Fluid Check Gear: 4 Pens and Strips
The check in the steps above needs a pen that reads moisture or a strip that reads condition, for DOT 3, DOT 4 and DOT 5.1 fluid, and the 4 picks below cover pens and strips.
Use rated jack stands on solid ground, wear eye protection with power and air tools, keep fuel-burning equipment out of a closed garage, and follow the manual for every tool. Read our Safety Disclaimer.
The ecocstm listing notes that metal additives in the brake fluid may cause the red light to come on, so a red light calls for another look.
FAQ: garage tools
How often should brake fluid be checked?
The Phoenix listing notes Tesla recommends checking Tesla brake fluid every 2 years with strips. For other vehicles, follow the vehicle manual.
What moisture reading means the fluid needs changing?
On the Xtruck listing, over 3% sets off the alarm and means the fluid needs changing, and the KAIWEETS listing shows red with a rapid beep above 3%. From 1.5% to 3%, the Xtruck listing says the fluid can still be used but needs frequent checks.
Do the picks here read DOT 3, DOT 4 and DOT 5.1 fluid?
Yes. Each pen and strip here states DOT 3, DOT 4 and DOT 5.1 fluid, and the KAIWEETS pen also states ENV4 and ENV6 fluid.
Do the strips check coolant as well as brake fluid?
Yes. The Phoenix strips are double-ended and check brake fluid and coolant, and the listing directs the user to check coolant as diluted 50/50 in the vehicle, never in full concentrate.
What batteries do the pens need?
The ecocstm and Xtruck pens each need a AAA battery that is not included, while the KAIWEETS pen runs on two AAA batteries included in the kit.
Related: brake fluid moisture pens, pneumatic brake bleeder kits, tools for changing brakes and the diagnostics and electrical hub.
