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Kevin C.
Kevin C., Subaru Master Tech.
Category: Subaru
Satisfied Customers: 1727
Experience:  34 years of Subaru service experience, ASE Master Technician.
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I have a problem with my Subaru wrx sti I have a code po558

Customer Question

Hello I have a problem with my Subaru wrx sti I have a code po558 this only popped up after I put a new alternator on
JA: Thanks. Can you give me any more details about your issue?
Customer: The issue is my engine management light is on and I found the code telling me is booster control cucuit pressure to high every time I clear this code it just comes up again the engine management light it's doing my head in now
JA: OK got it. Last thing — Subaru Mechanics generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: Subaru
Expert:  Gary replied 1 year ago.

Hi there,

Your P0558 is brake booster pressure sensor.

The cause is you have fitted the wrong alternator.

Your alternator should have 3 pins, the 3rd is for "smart charge".

Some aftermarket alternators may have the 3rd pin, but does nothing.

Go back to supplier.


Customer: replied 1 year ago.
hello ther i have a problem with my subaru wrx sti type uk i have a ECU CODE READING PO558 WHICH refers to brake booster pressure circuit high this only came up after i put a new alternator on my car and yes it is a 3 pin alternator and in sure it has a smart charge on it i have tried x2 alternators and i have cross refrenced them with the genuine subaru part number the alternator from subaru are 560.00 which i think is stupid price please can you tell me why does this code come up and what can i do to erase it or clear it the brakes are fine and i know the booster brake is no stiff to move its fine please please help me out im running out of ideas cheers ***** *****
Expert:  Gary replied 1 year ago.

Hi Dave,

I think you'll find your non-genuine alternator is the issue.

This code comes up when you fit a non-compatible alternator.

What was wrong with the original, can you put it back on to see if the code goes away?

Or have you asked Subaru, because they will tell you the same thing?

What is the price difference you're dealing with here?