Repair The Whining Steering Pump on a Subaru Impreza WRX STI

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If your STI's steering pump has started to whine, especially if it only makes noise when it's cold, there just might be an easy cure for the problem.

Perhaps the most likely source of the noise (and easiest to fix) is if you're low on power steering fluid. Check the level first, and if it's low replenish the fluid and test drive again to see if that cured it before going on the next step.

If the power steering fluid level is good, then follow along for the next-easiest repair you should consider. We're going to replace an O-ring that seals the power steering reservoir. This has to be the easiest repair you'll find on HowTune. So even if you've never repaired anything on your car before, don't hesitate to save yourself a service call bill and do this.

You'll have to obtain a new O-ring first, which may be the most difficult part of the repair. I looked around for sources other than Subaru for a comparable O-ring, but ended up buying it from a Dealership. Apparently it's a bit of an oddball size. Anyway, let's get stared.

  • Ratchet or screwdriver-style socket driver
  • 10mm socket
  • New O-ring. The Subaru part number is 34439FG000, which will cost under $2. If you'd like to try sourcing it from elsewhere, the reported size is 5/8 OD, 1/2 ID, 1/16 Gauge (please note I did not verify the size specs, as I bought the Subaru part).

A whining noise from under the hood, especially while you turn the steering wheel at a stop or slow speeds.

Why does it do this?


When an excessive amount of air enters the steering pump it often causes cavitation, which in turn is the source of the tell-tale whining sound. Air is introduced to the pump when the steering fluid level is low, or when the o-ring seal becomes brittle and fails.

Image 4434 from Repair the Whining Steering Pump on a Subaru Impreza WRX STI

Remove the fan belt shroud


Remove the 10mm bolt on the left and the 10mm nut on the right that hold the fan belt shroud on. The nut on the right should be loosened with your tool, then by hand so that the nut doesn't tumble down into the engine compartment abyss.

Image 4419 from Repair the Whining Steering Pump on a Subaru Impreza WRX STI

With the fan belt shroud removed, you'll have access to the top of the power steering pump. A single 10mm bolt secures a wire bracket and the steering fluid return hose. Remove this bolt.


Remove the 10mm bolt from the power steering return hose fitting (labeled "A" in the picture). Pull up on the fitting to access the o-ring.

Image 4425 from Repair the Whining Steering Pump on a Subaru Impreza WRX STI

Locate the O-ring.


As a precaution, slip a paper towel or other blocking device over the reservoir opening so it won't swallow the old o-ring when you drop it :) . Remove the old o-ring with a fingernail, small screwdriver, or similar. Don't be surprised if it breaks off - it's likely quite brittle.

Image 4431 from Repair the Whining Steering Pump on a Subaru Impreza WRX STI

Nearly Done.


Slip the new o-ring on the fitting. Re-seat the fitting and other bracket pieces to seal the reservoir. Replace and tighten the 10mm bolt. Replace the fan belt shroud an tighten the 10mm bolt and 10mm nut.


If it still squeaks after the O-ring swap, you may have excess air in the power steering system and may need to bleed it.

If the pump itself is leaking fluid, then you may need to replace the pump with a new/rebuilt one. But good news, there's another HowTune article available to help you with that.

There are 7 Comments.

Say Something.

Hi, do I need to bleed the power steering after replacing the o ring? People said its necessary to get the air out?


Jag009, I simply topped off the fluid level after replacing the o-ring and it was good to go. If you got lots of air trapped in the system before the swap, bleeding the system may be necessary. The o-ring swap is so simple - I would put it back together - no big deal if you discover it has to bled afterwards.


I had a squealing noise coming from the engine together with power steering failure when starting the engine from cold. It would stop after about thirty seconds. There was no leak of power steering fluid. Tried the remedies on youtube (making sure no air in the PS system, tightening the clip on the PS suction hose, almost bought an horrendously expensive new hose but didn't because there was not new one in the whole of the Subaru system). Then it struck me that the noise was actually the drive belt slipping on the power steering pump. It took five minutes to re-tension the belt and hey presto! no more squealing and power steering working perfectly. So I would advise anyone who experiences power steering failure accompanied by a squealing noise to check the power steering drive belt tension first.Hope this helps someone.


Thanks for the tip jonno999. And if you need a reference for adjusting the belt, see my post on "Replacing Accessory Belts" on this site.


Thanks for the great tip, jonno999. And if you need a reference for adjusting the PS belt, check my post for "Replacing Accessory Belts" on this site.


Ok, this seems easy enough, but you keep saying "reservoir" but do you mean the pump itself? The reservoir is the plastic reservoir where you put power steering fluid in. The pump and the fitting where you're putting the o-ring is going into the pump, right?


CameronH: Good catch; For clarity I've revised the text to read "pump" instead of 'reservoir".

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