started the car today and all the speedo warning lights were still on and all the dials were dead and no indicators or radio, but engine was running. strange. Restarted the car but was still the same.

Turned the engine off and waited about 20 minutes, restarted the car and it was all fine.

I did do a search on the forum but the symptoms relate to a Canbus error.

I've done the basic alternator checks and on idle without load its 14.4v (normal)

With a full load on the alternator (lights, heaters, fog light, rear screen, radio) the alternator voltage drops to 12.4v on idle.

If you raise the revs above 2k the voltage jumps back to 14.4v. Then drops back to 12.4v when you let it ldle.

I've tested the voltage at the alternator and the battery and all the readings are the same.

At first I thought it maybe the earth points under the battery so I've cleaned all these up.

The company i brought the alternator from is trying to tell me it sounds like the battery is at fault.

Its not the battery because I've tested that with a proper battery tester and the results are SOH 100%.

I'm no expert but does this sound like a faulty voltage regular on the alternator?

Vehicles a 1.2 8v 2006

You mention the seller of the alternator, was it replaced recently?
The measurements you make indicate the alternator is OK. Most will not provide enough current at idle to run full load and charge the battery.

You need to get diagostics like Multecuscan (www.multiecuscan.net) on the car to see what is going on.

Robert G8RPI.

g8rpi said:

You mention the seller of the alternator, was it replaced recently?
The measurements you make indicate the alternator is OK. Most will not provide enough current at idle to run full load and charge the battery.

You need to get diagostics like Multecuscan (www.multiecuscan.net) on the car to see what is going on.

Robert G8RPI.

Click to expand...

Hi Robert, the alternator was replaced in June 2020 and fitted by myself, its not a denso branded one just an aftermarket one. Its been fine until yesterday. (I've read aftermarket ones can be an issue on the GP)

I always thought a good working alternator should provide between 13.8v-14.4v at idle even when the cars electrics are under load.

What ive noticed is when it drops to 12.4v on idle, if I rev it to 2k the voltage jumps back up to 14.4v.

It depends on the alternator "gearing" (belt pulley sizes) idle speed and particular alternator. I would not expect full voltae at full load at idle on most older cars. If it's above 13.8V with sidelights on it's not faulty.
Exactly where you are measuring the voltag is important too. Across batterry terminals, Battery +Ve to engine block etc.

Robert G8RPI.

g8rpi said:

It depends on the alternator "gearing" (belt pulley sizes) idle speed and particular alternator. I would not expect full voltae at full load at idle on most older cars. If it's above 13.8V with sidelights on it's not faulty.
Exactly where you are measuring the voltag is important too. Across batterry terminals, Battery +Ve to engine block etc.

Robert G8RPI.

Click to expand...

I've measured voltage from the battery terminals and also direct from the alternator, both give same readings.

What I have noticed today is, when the alternator is cold (cold engine) the voltage under load is 13.8v. Soon as the alternator warms up you can see the voltage on the multimeter start dropping to battery voltage.

The idle speed may be higher when engine cold .

Lots of vehicles warm idle speed is not sufficient for full alternator output , you are asking for a lot of power by turning everything on. I think your alternator is ok if you have good voltage with all loads turned on and rpm around 1500 to 2000

I think you could be barking up the wrong tree.

Guys your absolutely right.

I feel like a right twit, had more time to test the system today. jackwhoo I never even thought about the revs being higher when cold ?. It makes sense now.

If I raise the revs just above idle at around 1k wheb the engine is warm the voltage goes back to 14.2v. This now makes sense why on a cold engine the voltage is 14.2v when fully loaded.

Hello everyone - Similar case, different voltages - 13.4 when car not running and 16-18v when running - I´ve had Fiats before and a similar issue was with the voltage regulator - Is it case with this one too ? IMO anything over 14v will destroy the battery in the longer run -

Fiat Evo 1.2 Mylife 8v 69ps