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HELP Alternator blue wire ECU issue?
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Old 22 May 2014, 03:03 PM   #1 (permalink)
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HELP Alternator blue wire ECU issue?

Hello all. Found a few different forums about this issue but no specific answers.

Got a 2005 WRX which had non-charging issues. Originally thought to be the battery, so this was replaced. Same non-charging continued so had the alternator replaced. Same issue continued.

The garage found that disconnecting the blue wire from the back of the alternator lets everything run fine, but when the blue wire is connected the system does not work and an engine warning light comes up on the dash. The error code shows a voltage issue in the charging system (unsurprisingly).

I know the blue wire runs back to the ECU. I have also read there is a smart charging system and that sometimes the charging system won't kick in until you place a load on the battery, such as sidelights or heater fan.

Anyone overcome this issue before or have more ideas about it?

Last edited by pageywrx; 11 Sep 2014 at 07:20 PM.
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Old 22 May 2014, 03:12 PM   #2 (permalink)
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Re: HELP Alternator blue wire ECU issue?

you know these are an intelligent charging system, when it senses a load it then charges, it doesnt just kick a charging voltage out all the time or say when it is on idle,
easiest way to test is with a voltmeter across the battery terminals and report the voltage :
1 on idle,
2 car running nothing on,
3 car running loads of load switched on,
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Old 07 Jun 2014, 01:19 PM   #3 (permalink)
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Re: HELP Alternator blue wire ECU issue?

you know these are an intelligent charging system, when it senses a load it then charges, it doesnt stay
a charging voltage out all the time or say when it is on idle,
easiest way to test is with a voltmeter across the battery terminals and report the voltage :
1 on idle,
2 car running nothing on,
3 car running loads of load switched on,[/QUOTE]

Finally hooked up a multimeter. This is cut and paste from another forum I posted on.

So, had a problem with the alternator not charging. Bought a brand new Bosch unit with the smart features i.e. blue wire compatible. Now, with the blue wire connected the alternator does not charge. I ran a multimeter back to the cabin to check whilst driving. The battery was reading 12.35V but just fell under load. So the old advice of sticking the lights or fan on does not seem to be doing anything. In addition, with the blue wire connected there is an orange engine warning light showing constantly. When I let off the gas, a handbrake/brake warning light comes on and also a battery warning light.

Disconnecting the blue wire solves the issues aside from the orange light remaining. The charge reaches up to 13.80V and the battery is retaining power

Last edited by pageywrx; 11 Sep 2014 at 07:20 PM. Reason: Tidy up
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Old 07 Jun 2014, 06:34 PM   #4 (permalink)
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Re: HELP Alternator blue wire ECU issue?

any chance of the answer to what I asked in post 2 so I can help,
No use PMing me to speed up the answer when you havent got what I asked for.
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Old 07 Jun 2014, 08:05 PM   #5 (permalink)
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Re: HELP Alternator blue wire ECU issue?

Quote:
Originally Posted by bugeye_bob View Post
any chance of the answer to what I asked in post 2 so I can help,
No use PMing me to speed up the answer when you havent got what I asked for.
Certainly.

Blue wire connected to alternator
Idle 12.35V and falling
Car running 12.35V (i.e nothing)
Under load 11.96V

...all slowly draining the power. No recharging occuring under any driving circumstances.

Blue wire disconnected
About 13.85V for everything. Compensated for load by bring back up to 13.85 ish.
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