Electrics: - Intermittent Alternator issue

Nomad0404 · Sep 1st, 2022, 12:35

Hi all,

I own a 54 plate XC90 (2003/4?) D5.

It has developed an issue where intermittently the Power System Service warning light comes on the dash along with the Red warning and battery warning lights.

If I understand the issue correctly the alternator is at times putting out less power than required and so the car starts draining the battery.

Without the warning lights being on the alternator was measured at 12.7 volts. However in the garage today it's being measured at 13.5 volts.

The alternator is new and has been replaced once on warranty. The battery is also new but I don't think the battery is the issue as this was swapped out but still had the issue.

I don't think it shows any warning issues when the diagnostic tool is plugged in.

Anyone have any suggestions what to check or what might be causing the issue.

Tannaton · Sep 1st, 2022, 13:47

Check the alternator overrun clutch pulley... these can start to fail intermittently and cause the issues you describe.

The electrical system on the early XC90's isn't as sophisticated in its charging systems as P3 models but actually that means its usually ultra dependable. At no time does the system deliberately discharge the battery, I would strongly suspect it's a physical issue (i.e pulley, belt tension) rather than an electronics fault.

When the alternator was replaced - was the pulley transferred over from the old one or a new one supplied?

Nomad0404 · Sep 1st, 2022, 14:15

I have no idea, probably transferred over. But I will get that checked.

Is there any chance is an issue with the linear regulator?

ltec · Sep 1st, 2022, 15:12

Is the new alternator genuine? If its aftermarket I would still be suspicious of it. I've had new aftermarket alternators give intermittent stupid problems on different cars but still tested ok. I prefer to get the old alternator done up.
It shouldn't be reading as low as 12.7. That sounds more like the battery voltage.

Tannaton · Sep 1st, 2022, 16:42

Quote:

Originally Posted by ltec

It shouldn't be reading as low as 12.7. That sounds more like the battery voltage.

That's another good point - when the engine is running the voltage should be between 13.5 and 14.1 I think. 12.7 is just the battery on it's own.

Sep 1st, 2022, 12:35	#1
Nomad0404 New Member Last Online: Sep 1st, 2022 14:15 Join Date: Sep 2022 Location: Medway	Intermittent Alternator issue Hi all, I own a 54 plate XC90 (2003/4?) D5. It has developed an issue where intermittently the Power System Service warning light comes on the dash along with the Red warning and battery warning lights. If I understand the issue correctly the alternator is at times putting out less power than required and so the car starts draining the battery. Without the warning lights being on the alternator was measured at 12.7 volts. However in the garage today it's being measured at 13.5 volts. The alternator is new and has been replaced once on warranty. The battery is also new but I don't think the battery is the issue as this was swapped out but still had the issue. I don't think it shows any warning issues when the diagnostic tool is plugged in. Anyone have any suggestions what to check or what might be causing the issue.

Sep 1st, 2022, 13:47	#2
Tannaton Bungling Amateur Last Online: Today 19:12 Join Date: Aug 2014 Location: Beverley, East Yorks	Check the alternator overrun clutch pulley... these can start to fail intermittently and cause the issues you describe. The electrical system on the early XC90's isn't as sophisticated in its charging systems as P3 models but actually that means its usually ultra dependable. At no time does the system deliberately discharge the battery, I would strongly suspect it's a physical issue (i.e pulley, belt tension) rather than an electronics fault. When the alternator was replaced - was the pulley transferred over from the old one or a new one supplied? __________________ 2011 XC90 D5 Executive 2003 C70 T5 GT 2012 Ford Ranger XL SC 1977 Triumph Spitfire 1500 1976 Massey Ferguson 135 Last edited by Tannaton; Sep 1st, 2022 at 13:51.

Sep 1st, 2022, 15:12	#4
ltec Member Last Online: May 27th, 2023 22:47 Join Date: Feb 2015 Location: Northern Ireland	Is the new alternator genuine? If its aftermarket I would still be suspicious of it. I've had new aftermarket alternators give intermittent stupid problems on different cars but still tested ok. I prefer to get the old alternator done up. It shouldn't be reading as low as 12.7. That sounds more like the battery voltage. Last edited by ltec; Sep 1st, 2022 at 15:16.

Sep 1st, 2022, 14:15	#3
Nomad0404 New Member Last Online: Sep 1st, 2022 14:15 Join Date: Sep 2022 Location: Medway	I have no idea, probably transferred over. But I will get that checked. Is there any chance is an issue with the linear regulator?

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