There's a pump that runs when the car is on to pressurize the hydraulics, right?

When bleeding the brakes, should the car be on or off so this pump is on or off?

I'm specifically talking about a Honda '03 if that affects the question.

  • Are you asking about bleeding the brakes at the wheels to stiffen the system? Or about a system flush or ABS module replacement? My answer addresses the former, Larry's addresses the latter.
    – Ehryk
    Aug 25, 2012 at 19:55
  • I was talking about to get air out of the system, not for a full flush. I did see elsewhere that you should activate the ABS to get the fluid out of there if you're doing a flush. I picked the answer I did because for some reason the explanation gave me more confidence I should be bleeding them with the pump off to get the air out. Thanks to both of you for your answers.
    – RLZaleski
    Aug 26, 2012 at 18:22
  • @RLZaleski You should follow what the manufacturer recommends for the bleeding procedure. I spent an hour trying to bleed the brakes on my Galant once because like most of the comments here it was "colloquial knowledge" that you didn't need the engine running. Mitsubishi states that the engine NEEDS to be running to prevent damage to the ABS System. Find out what the Manufacturer recommends and ignore anything else you read/hear.
    – NitrusInc
    Apr 9, 2018 at 12:18

6 Answers 6


If what you meant was bleeding the brakes at the calipers to remove air from the system, you should bleed the brakes with the car off. While 'pump' was the wrong word to use, the brake booster runs off the engine vacuum (it's a large diaphragm that multiplies brake force), and this should not be active. You can feel the difference by pumping the brakes a few times with the car off, then pushing with a medium effort on the brake pedal while starting; once the engine starts, the same effort will sink the pedal further and put more force on the hydraulics.

When you bleed brakes, you want to have an assistant push the brake pedal while you crack open the line and then close it BEFORE the pedal hits the floor (or you'll introduce air into the caliper). If the engine is running, not only is this unsafe (front axles can spin, hitting your hands if the front is in the air or moving off the stands if the rear is up), but it drastically changes the pressure at which the fluid will shoot out of the calipers and shrink the time to close the bleeder screw before the pedal hits the floor.

Summary: Bleed brakes (at the calipers) with the engine off.

  • Are you suggesting that people specifically disregard the manufacturers instructions for the bleeding procedure or are you speaking about this Honda model specifically?
    – NitrusInc
    Apr 9, 2018 at 12:20

The only pump that runs would be for the ABS system. If you are trying to bleed that system (ABS) you would need to make the pump run, if you are just bleeding the base brakes you would not need the pump to run.

For example you changed a caliper and you need to bleed the brakes then no need to make the pump run. If however you were changing the ABS modulator you would need to make the pump run as well as take some additional steps in the bleeding procedure.

For clarification based on @Ehryk's comment.

Honda uses an ABS motor to pressurize the accumulator in the ABS system. Factory bleeding procedures for the ABS system and for brake fluid replacement both require the motor to be run at specific points in the bleeding procedure. The can be done by starting the engine and letting it run for a minute or so, or by hooking up a computer to the car and commanding the motor to run.

Here is a link to a video on Youtube explaining the procedure.

More info here although it's for an earlier model car. I think the 2003 has the motor mounted directly to the modulator assembly.

  • You're right technically, that no pump runs for the brakes, but your answer is clearly misleading. The brake booster runs off engine vacuum and makes a large difference when bleeding brakes.
    – Ehryk
    Aug 25, 2012 at 10:20
  • @Ehryk I am not refering to the brake booster. I am talking about the ABS pump motor. The vacuum booster doesn't "run" as the OP stated. Aug 25, 2012 at 19:12
  • @Ehryk I have updated my answer with additional information explaining the ABS pump motor Aug 25, 2012 at 19:50
  • Thank you for clarification. You can see that the video is about brake fluid replacement; and though this could have been what the OP meant, I'd say 'bleeding brakes' in the colloquial sense refers to caliper-level bleeding ~95% of the time. Someone who replaced their own ABS module and/or was flushing the entire system probably would not be asking how to do it on SE.
    – Ehryk
    Aug 25, 2012 at 19:53
  • @Ehryk Honda recommends brake fluid replacement as part of their scheduled maintenance. This is accomplished by bleeding the brakes and includes bleeding the accumulator. Since the OP asked about a pump I assumed that was what he was doing. Aug 25, 2012 at 20:07

According to AutoZone(AllData) and wherever EBSCOHost gets it's repair data:

Repair Guides for the following vehicles were referenced as they were available:

  • 2003 Honda Civic

  • 1995 - 2000 CRV/Ody

  • Honda Accord 2007-2008

  • Honda Civic 2007-2008
  • Honda S2000 2007-2008

Brake System Bleeding

NOTE: - Do not reuse the drained fluid.

  • Always use Honda DOT 3 Brake Fluid from an unopened container. Non-Honda brake fluid can cause corrosion and shorten the life of the system.

  • Do not allow dirt or other foreign matter to contaminate the brake fluid.

  • Do not spill brake fluid on the vehicle, it may damage the paint; if brake fluid does contact the paint, wash it off immediately with water.

  • The reservoir on the master cylinder must be at the MAX (upper) level mark at the start of the bleeding procedure and checked after bleeding each brake caliper. Add fluid as required.

  • Make sure the brake fluid level in the reservoir is at the MAX (upper) level line (A).


  1. Slide a piece of clear plastic hose over the first bleed screw, and submerge the other end in a container of new brake fluid.

  2. Have someone slowly pump the brake pedal several times, then apply steady pressure.

  3. Starting at the left-front, loosen the brake bleed screw to allow air to escape from the system. Then tighten the bleed screw securely.

  4. Repeat the procedure for each wheel in the sequence below following until air bubbles no longer appear in the fluid.

  5. Refill the master cylinder reservoir to the MAX (upper) level line.


  1. Front Left
  2. Front Right
  3. Rear Right
  4. Rear Left


  • Front: 7 ft/lbs

  • Rear: 5 ft/lbs

There is no mention that the engine needs to be running. AutoZone's repair guide for the CRV stated that ABS and Non-ABS Vehicles had the same bleeding procedure.

I would still urge you to acquire a Factory Service Manual to ensure that the procedure can safely be performed with the engine OFF, though I suspect that the information available is providing a decent level of certianity if you wish to continue without Manufacturer confirmation.


If the engine is running, not only is this unsafe (front axles can spin, hitting your hands if the front is in the air or moving off the stands if the rear is up), but it drastically changes the pressure at which the fluid will shoot out of the calipers and shrink the time to close the bleeder screw before the pedal hits the floor.


First of all, when bleeding brakes its always good to look at each car manufacture's recommendation. As far as having the car running, that's only needed if you are doing a complete flush after changing out a failed ABS modulator. Afterwards, you would still need to do a bleeding process with engine OFF as well. If you have someone Pumping up the pedal, make sure the pedal does not go all the way to the floor. I've seen professionals jump up and down very hard while "pumping" up the pedal which is WRONG. Apply a slow pressure when pumping up the pedal. I use a cut off piece of 2x4 underneath pedal to ensure the pedal doesn't hit the floor. Hope this helps.


I have a 2007 Equinox - the right front caliper was bad. I tried to bleed the caliper for about an hour with car not running - didn’t work. I started the car and I got the air out. So whoever says the car doesn’t have to be running is wrong.

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