Should I bleed brakes with the engine on or off?

Best practice is to bleed the brakes with the engine off. This approach isolates the hydraulic system and provides a stable pedal feel during the procedure.

Bleeding brakes correctly matters for safety: the brake booster in a running engine relies on vacuum to assist braking, and that can complicate the bleeding process if the engine is left running. Some vehicles or specialized tools may permit bleeding with the engine running, but that is less common and often requires specific instructions from the manual. Always check your owner's manual before starting.

Bleeding brakes with the engine off

Using the engine-off method gives you the most predictable pedal feel and is the standard approach for most cars. Below are the typical steps people follow on a single-circuit hydraulic system.

1. Park on level ground, apply the parking brake, and chock the wheels. Gather fresh brake fluid of the correct type (DOT 3/4 as specified), a clear container, bleeder hoses, and a wrench for the bleed screws.


2. Open the hood and locate the brake fluid reservoir; clean the cap area to prevent contamination. If the fluid is low, top up to the max line with the correct fluid. Do not overfill.


3. Attach a clear hose to the bleed screw on the wheel farthest from the master cylinder (usually the rear passenger side). Place the other end of the hose into a container to catch the old fluid.


4. Have a helper firmly press and hold the brake pedal to the floor (do not let the pedal hit the floor on its own). With the pedal held down, crack the bleed screw open slightly to allow air and old fluid to escape. When fluid runs clear and without air bubbles, close the bleed screw before releasing the pedal.


5. Repeat the process until only clear fluid comes out with no bubbles. Move to the next wheel in the sequence (the wheel farthest from the master cylinder first, then the others in the vehicle’s recommended order). Check the fluid level periodically and top up as needed.


6. After bleeding all four wheels, wipe up any spills, reinstall reservoir cap, and test the brake pedal with the engine off. The pedal should feel firm; if it’s spongy, re-check for remaining air or leaks.


7. Perform a cautious road test at low speed to ensure there are no leaks and that braking is firm and predictable. Re-check fluid level and top up if necessary.

In practice, many garages follow the “farthest wheel first” rule and use the two-person method described above. If you’re using a pressure bleeder, the steps may vary; always follow the tool’s instructions.

Bleeding brakes with the engine on

Bleeding with the engine running is generally not the default recommendation, but there are scenarios where it’s used — for example, when a vehicle’s brake booster relies on engine vacuum and you’re using a shop tool that requires the engine to run, or when a manual bleeding sequence specifically calls for it. If you must bleed with the engine on, proceed with caution and consult the vehicle’s service manual.

1. Ensure the vehicle is on a flat surface with the parking brake engaged and wheels chocked. Have a helper ready and the correct brake fluid on hand.


2. Start and run the engine at idle (roughly 600–900 rpm) to maintain brake booster vacuum. Do not rev the engine.


3. As with the engine-off method, attach the clear hose to the far bleed screw and place the other end in a container.


4. Have the helper press and hold the brake pedal firmly to maintain pedal position while you slowly open the bleed screw to release air and old fluid. Close the screw before the pedal returns to the floor.


5. Proceed to the remaining wheels in the same order, keep the reservoir topped up, and monitor for air bubbles. Be mindful that the pedal feel will be different due to the booster assistance.


6. When finished, turn the engine off and re-check the system. Re-ble if you suspect air remains or after a long drive, then test the brakes at a safe speed to confirm proper operation.

Note that this method is less common and may not be suitable for all vehicles. Check your service manual and consider having a professional perform this step if you’re unsure.

Additional considerations

- Brake fluid type: Use the fluid specified by your manufacturer (DOT 3, DOT 4, or DOT 5). Do not mix different types, and avoid letting the fluid contact painted surfaces.

- ABS and computer-assisted brakes: If your vehicle has ABS or electronic brake modules, a simple gravity bleed may not purge all air. You may need an ABS bleed procedure using a scan tool or a professional-grade pressure bleeder. Always consult the service manual.

Summary

For most drivers performing a basic brake bleed, the engine should be off. This setup provides a predictable pedal feel and avoids complications from the brake booster’s vacuum. If you encounter unusual pedal behavior, persistent air, or your vehicle’s manual specifies otherwise, stop and consult a professional. Keeping to the recommended procedure and using the correct fluid will help ensure safe and effective braking performance.

What is the correct way to bleed your brakes?

Bleeding Your Car's Brakes Takes Just 5 Steps:

1. Step 1: Change the brake fluid.
2. Step 2: Loosen the bleeder valve.
3. Step 3: Attach a clear plastic tube to the bleeder bolt.
4. Step 4: Have a partner press down on the brake pedal to drain the fluid.
5. Step 5: Repeat until new, clear, bubble-free fluid comes from the bleeder tube.

Do you bleed brakes with an engine on or off?

You should bleed the brakes with the engine off because the running engine provides vacuum boost, which can interfere with the bleeding process and potentially introduce air into the system. With the engine off, you can properly pump the brake pedal to build pressure and evacuate air from the lines. 
How to bleed brakes with the engine off

• Park and prepare: Ensure the vehicle is parked on a level surface, turn the engine off, and engage the parking brake. 
• Pump the pedal: Have your partner pump the brake pedal several times until they feel resistance. 
• Hold the pressure: Instruct your partner to hold the brake pedal firmly to the floor. 
• Open the bleeder valve: Open the bleeder valve on the caliper or wheel cylinder until fluid stops flowing and then close it. 
• Repeat: Continue this process until no air bubbles are visible in the fluid being expelled. 

Do you pump brakes with a car on or off?

You should pump the brakes with the car off after performing work like changing brake pads, but you should pump them with the car on in most other situations to check for functionality, but be aware of the brake booster effect. 
When to pump brakes with the car off

• After a brake job: If you've pushed the caliper pistons back to fit new pads, pumping the brakes with the car off is necessary to pump the fluid and seat the pads against the rotors. You should do this before driving to ensure a firm pedal. 
• During brake bleeding: When bleeding the brake system to remove air, the car should be off. The pressure from the brake booster (which is active when the car is running) can affect the process and could be unsafe. 

This video demonstrates how to pump the brakes after a brake job to seat the pads: 52sExpertVillage Leaf GroupYouTube · Dec 17, 2020
When to pump brakes with the car on

• To check for issues: Pumping the brakes with the car on can help you check if the power brake booster is working correctly. If the pedal feels firm at first, and then sinks when you start the engine, it means the booster is working. 
• In stop-and-go traffic: Pumping the brakes when the car is on is a normal and necessary part of driving to slow down or stop. It is not bad to do it in this context. 

What to avoid

• Continuously pumping brakes with the car on: This can lead to brake overheating in a situation like heavy downhill driving. In such cases, using a lower gear is recommended to control speed instead of "riding" the brakes. 
• Pumping the brake pedal all the way to the floor: This could damage the master cylinder. 

What not to do when bleeding brakes?

Here are some of the usual errors to avoid when bleeding the brakes:

1. Using the Wrong Type of Brake Fluid.
2. Spilling Brake Fluid on Brake Pads.
3. Overfilling the Master Cylinder Reservoir.
4. Stripping the Bleeder.
5. Letting Moisture and Debris In.
6. Wrong Bleeding Sequence.
7. Overtightening the Bleeder Screw.