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S40 T4 2002 Alternator & Charging details

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Old Sep 4th, 2018, 19:41   #1
harrympotter
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Default S40 T4 2002 Alternator & Charging details

Evening all,

The mighty T4 pottered back home with the wife onboard with no dashboard indications and relays clicking away.


Put Volt meter on battery 9v OMG ! - So first action, battery dead, EuroCarPart 40% payday code. Battery replaced.


Volt meter on BATT 12.6v. Starts the engine.... 12.6v. Alternator not charging!!!


PREVIOUS HISTORY. (last owner receipts) Less that a year ago £300 of fault diagnosis work for a none charging Alternator. Then next months bill new Alternator £360. Geeeez.


So, wife takes my V70 for next few days...

Next morning (after NO rectification work) Starts the engine 14.6v !!! Alternator is now charging.

I ordered a Cigarette light in car Volt meter to monitor this.....


Today car returned home and wife reported I only ever saw 12v (in car Volt meter).


So intermittent charging... There is a White (I think) wire connected to the Alternator, is my understanding that this is the Ignition / Excite cable? that tells the Alternator to run/charge.

With the fault apparent today I have 1.8v at this white ALT Excite wire, when the Alternator has a charging period, I see 12.4v at the white cable then 14.4v once engine is started.


Where is this Excite/IGN signal from ECU? ECM? Ignition?

Is it SMART ECU controlled charging..... ON and OFF as needed?

Can I find another 12v IGN signal and provide this to the alternator to activate charging? or will this constant charging cook / over charge the BATT.


Thanks in advance
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Old Sep 4th, 2018, 20:17   #2
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""White excite cable 13.8v when 14.4v charging is active. ""
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Old Sep 4th, 2018, 21:02   #3
canis
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The white wire goes to the ignition lamp on the instrument cluster. If I remember rightly it doesn't go to the ECU at all, but I might be wrong. In any case, there's nothing clever going on, when the alternator is spinning it should be delivering charge on it's big red wire. It leads from the alternator ultimately to the battery, but via the starter motor. Make sure it's securely connected.

14.4 volts is fine, isn't it?

You might also want to check the condition of the battery earth strap. Several people have reported corroded earth connectors. These cars are getting old these days.
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Old Sep 5th, 2018, 17:56   #4
harrympotter
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Default Wiring Diagram

Thanks, I paid £4.99 for the Haynes destroy it yourself online manual.

Hope I can attach / people can see.


There are only Three connections to the ALTERNATOR (3)

1. WHITE from the Dashboard cluster (Charing warning lamp) & Airbag module.

2. RED to starter and BATT.


3. Earth.


As per the diagram, flow arrow is to the Alternator. (6/H4 instrument cluster) and (13/D8 Airbag control module)


the feed from Instrument cluster (55) - circuit uses a micro processor (O) via the warning lamp (m).


As per the Black arrow of flow, the Alternator needs this signal (I think).

Going to check earths on ALT and BATT,

Any ideas on this white signal ? to excite the Alternator? Micro processor (O). [ATTACH]Instru Cluster.JPG[/ATTACH]
Attached Images
File Type: jpg Starting Diag.JPG (54.3 KB, 11 views)
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Old Sep 5th, 2018, 20:08   #5
canis
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Dude, i'm telling you from personal empirical actual experience; The white wire goes high when the alternator is producing charge. That's how it extinguishes the ignition lamp, which is on by default. It is the red wire which delivers the charge to your battery. End of.
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Old Sep 5th, 2018, 22:15   #6
harrympotter
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Sorry, you are right I'm chasing my tail.


Disconnecting the White lead just turned the ALT / BATT no charging red warning symbol on and off as you connected and disconnect from the ALT.


Today is a charging (working day) 14.46v.


ALT is earthed through its body to the engine - engine earthed to gearbox and blue earth strap from gearbox to BATT. Will inspect and clean up tomorrow.
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Old Sep 5th, 2018, 22:33   #7
pierremcalpine
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For what it's worth, I ended up replacing my red cable last year. it had almost completely frayed where it bends near the battery. Best to replace end-to-end with a know good cable from wreckyard or new.
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