P0558 - Alternator Circuit Low Fault
 

Hi all,

I'm brand new here so please be gentle with me. I'd ask you to please bear in mind that 1). I'm not doing this job because 2). I have no mechanical or electrical knowledge whatsoever!

I own an Impreza STi Type-UK, model year 2005 but first registered April 2006. The original alternator has failed (and killed the battery in the process) and has been replaced by my local garage with a reconditioned Delco Remy DRA0366 alternator and a brand new Lucas Premium LP005L battery. The battery light is lit when the ignition is on but the car is not started and then goes off when the car is started. On starting the car, after a few seconds the engine diagnostic light comes on and the logged error is "P0558 - Alternator Circuit Low". The new battery has been tested as good but slightly discharged, presumably due to the effects of what I've written in the next paragraph.

With no user-switchable electrics turned on, I've been told that the voltage in the charging circuit remains steady at 12.5v or thereabouts. When something electrical is turned on (heater fan, lights, A/C, heated screen, headlights or the whole lot), the voltage never gets above 13.07v when it would be reasonable to expect it to be somewhere in the region of 14v to 14.5v. Obviously this means that the battery would progressively become more and more discharged in real world use. Clearing the log just forces the cycle to start again with the engine diagnostic light.

The garage has a lot of high quality diagnostic equipment and the person assigned to the job (the garage owner) has a lot of auto electrical experience too but he's struggling without a wiring diagram and a pin assignment diagram. He's tried to get what he needs in the way of diagrams from sources he uses or knows within the trade but up to yet he's drawn a blank, no-one seems to have any. So he tells me he's loathe to start sticking his probe on wires because he doesn't know what signal voltages and waveforms (?) everything is running at - I'm sure that will mean something to someone? He's told me he can't disconnect the engine management from the alternator and force it to think its been told that a full load is required from it until he knows what wires are doing what.

In the interests of trying to get my car fixed and trying to limit what is already turning into a catastrophic bill, I thought I would ask on here for help. I know there are some extremely knowledgeable and helpful people here so any help and/or information and/or UK wiring diagrams for this problem would be gratefully received.

Thanks in advance https://www.scoobynet.com/images/icons/icon14.gif

Roger

I have the same fault - 06 Impreza WRX
 

Hey buddy, I'm having this exact same problem. Had a fault with original alternator overcharging. Swapped battery and alternator. Now getting the engine light with code "alternator circuit low". Did you end up finding the fix by any chance? It would be really appreciated!

Kind regards,
Brandon 😀

You need to check out his "other" thread

https://www.scoobynet.com/lighting-a...l#post12008548

Cheers mate, so pretty much I need a new genuine alternator

That would appear to be the gist of it, although Buzzard8 used a "Blueprint" version.

The Blueprint alternator I had fitted has worked perfectly since it was fitted. It took a long time to get to the Blueprint conclusion but I do recommend one.

Also - buy a decent battery. Perhaps an Exide one.

I'm from Australia and don't think we have blueprint here, my auto elec mate said the one I bought is genuine reconditioned but they must have used an aftermarket regulator or something. Already bought a new good battery. I'm just gonna return the second alternator and try a third one from a different supplier who is confident it will work properly, cheers for all your help guys, without seeing this I don't know what I would have done because everyone was starting to blame the car after the second alternator was put in. Saying I might need a new ECU and all sorts lol

I would be very surprised if it's the car from my own personal experience. The issue with my car was getting the EMU to accept the new alternator. It wouldn't work with anything aftermarket and getting a genuine Subaru alternator was a non-event. Hence the Blueprint alternator.