How to bleed power steering correctly?


New Member
Feb 15, 2021
02 Mustang GT, 155k

TLDR; Perpetual power steering whine when at idle and especially when braking and turning.

Had a bad brake fluid leak that ended with no brake pressure at all. Replaced caliper and line and bled system and that fixed that and the pedal felt normal.

However, as soon as I started it it started making a very loud power steering noise. It gets worse when turning and when braking. These cars have a hydro boost brake booster so the brakes are related to the power steering fluid in ways. I don’t think the steering is any worse now, but the brakes feel different, you go further on the pedal to get the same braking pressure. The noise is really bad even just at idle.

The level of fluid is fine. I attempted to bleed the ps system by turning wheel lock to lock 10 times, and pumping brake 10 times with res open and car off but that didn’t really do anything.

Could it really just be air in the system? Maybe I’m not bleeding it right. And why did it happen after brake replacement?

After attempting to bleed it a second time the noise was a little less worse when idling and turning but still awful when braking. I looked at the reservoir after I started it and turned it off and there were tons of bubbles.

(This is my first post so please let me know if I'm posting in the wrong place)
  • Sponsors(?)

StangNet created a new car social app called knowmoto! Add your Mustang or post a photo in the knowmoto app and enter for a chance at a $100 gift card from LMR. Click the LMR Logo for more about the knowmoto Mega Thread!


i'm familiar with penetration
Mod Dude
Feb 18, 2001
Here's the bleeding procedure (taken from another thread I recently read). The system itself is pretty self-bleeding, so it's entirely possible the pump is beginning to fail. BTW, depressing the gas pedal to the floor will also prevent the vehicle from starting (it signals flood clear to the ECU and does not fire the fuel injectors.

1. NOTE: The Hydro-Boost power brake booster is generally self-bleeding, and the following procedure will normally bleed the air from the power brake booster. Normal operation of the vehicle will further remove any additional trapped air. Fill the power steering oil reservoir with MERCON (R) Multi-Purpose ATE XT-2-QDX or MERCON (R) equivalent.

2. Remove the Powertrain Control Module (PCM) fuse to prevent the engine from starting.

3. Crank the engine for several seconds.

4. Check the fluid level in the power steering oil reservoir and add if necessary. Install the Powertrain Control Module (PCM) fuse.

5. Start the engine.

6. With the engine running, turn the steering wheel from stop to stop twice. Turn the engine off.

7. Depress the brake pedal several times to discharge the accumulator.

8. Repeat Steps 5 and 6.

9. If foaming occurs, stop the engine and allow the foam to dissipate.

10. Repeat Steps 5 and 6 as required, until all the air is removed from the system (when the foaming stops).