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I have a problem with my Subaru wrx sti I have a code po558…

Customer Question
Hello I have a...

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

Mechanic's Assistant: Thanks. Can you give me any more details about your issue?

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

Submitted: 2 years ago.Category: Subaru
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Answered in 28 minutes by:
3/1/2016
Subaru Mechanic: Gary, ASE Certified Technician replied 2 years ago
Gary
Gary, ASE Certified Technician
Category: Subaru
Satisfied Customers: 2,011
Experience: Senior Technician
Verified

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.

Gary

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Customer reply replied 2 years 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 ***** *****
Subaru Mechanic: Gary, ASE Certified Technician replied 2 years 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?

Gary

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