Battery warning light stays on as soon as I start the engine.

[LFY]

Hello.
Recently, I had a very annoying issue that stopped me from driving my car. About 5 days ago, I wanted to go out. I started the engine and battery warning light illuminated on the dashboard. I let the engine idle for a few minutes because I thought this will charge the battery and the light would turn off but it didn't. I turned the engine off and popped the hood. I checked for any obvious issues. The alternator belt was ok and there was nothing wrong except for one thing. I checked battery cables and noticed that the + cable is somehow loose, not extremely loose but I could turn it with my hand and remove it. I tightened the cable in its place with a wrench and tried starting the car again to see if this solves the problem but after about 15 minutes of running the engine at 2000 - 2500 RPM, the warning light didn't go out. I gave up and turned the engine off to prevent from draining the battery.

This is the whole story that happened to me. Now, what do you think could be the problem? Alternator failure? Voltage regulator?
I have a multimeter to check the voltage but I'm so unlucky because my multimeter has stopped working too!

[Hell Razor5543]

The multimeter probably needs a new battery (usually, but not always, a 9V PP3 battery). Once you have that working you should be able to tell if the alternator is working. With the engine off the battery should be around 12V, but with the engine running that will be around 14.4V.

[LFY]

The multimeter probably needs a new battery (usually, but not always, a 9V PP3 battery). Once you have that working you should be able to tell if the alternator is working. With the engine off the battery should be around 12V, but with the engine running that will be around 14.4V.

I'm sure the alternator doesn't work because the battery is weak and the car runs on battery alone without being charged. I replaced voltage regulator brushes about 1 year ago but I have driven my car no more than 4000 kms since then. I think even fake brushes should last much more than that (at least 30K kms).

[Hell Razor5543]

How old is the battery? They do have a finite working life, and will eventually fail.

[LFY]

How old is the battery? They do have a finite working life, and will eventually fail.

One year and some months. Not too old. I'm really disappointed because the last time I wanted to replace voltage regulator brushes, I had to remove so many things to gain access to the alternator. I removed throttle body, intake manifold, Fuel rail and some hoses! It was a burden! I don't have the mood to disassemble the whole parts again!

[Hell Razor5543]

I have only changed the brushes on one alternator, and that was on my BX. I found it was easy to do by removing the alternator from the car.

[LFY]

I have only changed the brushes on one alternator, and that was on my BX. I found it was easy to do by removing the alternator from the car.

My alternator is located somewhere that is not easily accessible. My problem is that I'm not sure whether it is the brushes or something else that has caused the problem. I don't want to remove the alternator and found that the problem lies elsewhere!!

[white exec]

Running an alternator without (good) battery connection can damage the alternator (and other electrical items), as the alternator cannot properly sense battery/system voltage.

Check alternator output voltage (c.14.4V), and whether it's outputting meaningful current (switch on lots of load at idle, then increase revs to 2000+ and look at whether interior lights (for example) get brighter.

[LFY]

Running an alternator without (good) battery connection can damage the alternator (and other electrical items), as the alternator cannot properly sense battery/system voltage.

Check alternator output voltage (c.14.4V), and whether it's outputting meaningful current (switch on lots of load at idle, then increase revs to 2000+ and look at whether interior lights (for example) get brighter.

You frightened me! Do you mean the ECU or engine Sensors might have failed too?!!
What will happen to an alternator to run without (good) battery connection? I mean which parts of it will fail most likely? Voltage regulator? Brushes? Diodes?

[Hell Razor5543]

The battery also helps to smooth out the voltage spikes, so if there is a problem with the battery circuit voltage surges could get into the electronics and damage them.

[white exec]

Best thing to do is to make the connections at the battery and alternator clean and secure, and then check what is working and what isn't.
Check voltage at the battery terminals:
- engine not running, batt voltage will be around 12
- engine running, 1500-2000 rpm, voltage should show 14.4 or thereabouts.

A clip-on ammeter (eg Sealey clip-on 75-0-75 amp, available on Amazon) allows you to see what the alternator is outputting (or what is flowing into/out of the battery) without cutting into cables. A handy tool, not expensive.

Don't panic about damage to other items until you know that something is amiss. Usually, the casualty is the alternator internals.

Alternator should have several decent and stable connections:
- main output cable to batt+
- a connection to IGN switch, showing battery voltage when IGN is switched on
- a connection to the IGN (charging) warning light, and from there to an IGN-on supply
- maybe (maybe) one other connection to batt+, which senses battery voltage; this connection does not exist on many modern alternators.

[wheeler]

Remember if there is no decent charging voltage at the battery you also then need to check the output directly at the main +ve terminal on the alternator with your negative multimeter lead on the alternator casing to rule out a problem with the alt +ve to battery +ve lead and earth connections.

[LFY]

Yesterday, I started the engine and hit the alternator with a metal rod but it didn't react to the blow. When brushes are consumed, the alternator will usually run for a few minutes by hitting it with a metal rod but in my case it didn't. Does this mean that the problem is not related to brushes? What could be the main culprit? The whole voltage regulator assembly?

[white exec]

Well, it's one way to start the diagnosis.
Wonder whether Peugeot have a workshop repair code for that?

[ekjdm14]

Well, that's A way to check, I suppose. Have you got the multimeter working yet? Could it be the light is on but it's still charging after all? That's the main reason to use the actual test gear, stops you from getting led astray & it wouldn't be the first time a warning lamp has told lies (for example, 1.9TD oil level warnings/early Xantia water-in-fuel warnings to name just two common ones).

Really you need to check if it is charging first off, and assuming not, check for any output at the alternator itself as mentioned above as well as any signal voltages it needs. Then you can work from the results you get, it may just be a blown fuse preventing the alternator from "seeing" that the ignition is on but the multimeter should be your first priority to fix/replace