Voltage issue, need help determining if alternator problem

My brother in law's E46 2003 318i is experiencing some voltage/battery/alternator/wiring issues I believe.

Occasionally and completely random, the red battery light will turn on for a couple of seconds or even minutes, then go off. Using the OBC voltage option #9, I get the following readings

12.3v on Ignition on, engine not running, assume battery is ok with this?
14.1v on engine running/idle, no electrical equipment on
13.7v on engine running/idle with heater, lights, etc on

It also appears that when I start the car, it takes some seconds for the alternator to reach 14.1v, it starts from 13v and rises to 14.1 is that normal? Also, if I rev the engine and let the throttle off, voltage drops to 13.7v until the engine rpm stops to idle (750rpm).

Checked the wiring seem nice and tight. The car's also experiencing some odd behavior which I think is also related to voltage fluctuations, which is random DSC AND ABS lights on, random rear tailight out warning.

No CEL codes stored.
Car has 55000 miles

Have you ever considered the voltage regulator..........

If the problem is intermittent, I'd suspect a ground problem, but it can be the alternator, or even an issue with the belt or the tensioner. Is there noise when this occurs, heavy steering, anything else besides the battery light?
The OBC test#9 readings look normal to me, but I suppose you didn't have a chance to check the voltage while the red light was ON.

Originally Posted by E46Mango

Have you ever considered the voltage regulator..........

Well yes, the car has the Valeo alternator which IIRC does not have a replaceable VR so I want to be sure before replacing parts.

Originally Posted by Megalocnus

If the problem is intermittent, I'd suspect a ground problem, but it can be the alternator, or even an issue with the belt or the tensioner. Is there noise when this occurs, heavy steering, anything else besides the battery light?
The OBC test#9 readings look normal to me, but I suppose you didn't have a chance to check the voltage while the red light was ON.

Belt/tensioner checked ok, no noise or heavy steering. Just the battery light and -what I guess related to voltage- the random DSC/ABS flashing. I will check the cabling behind the alternator again to see. I showed to the owner how to get to the menu so that when it happens again he will tell me the readings.

I don't think Alternator should take time to build up voltage. It should be pretty much instant. Either a slipping belt or alternator that's about to sh1t the bed

Depending on the mileage and especially if it is the stock alternator, I think it's time to replace just for PM sake. Wouldn't want to get stranded just because of an alternator.

Probably a good idea to replace the battery if it is still the stock one as well.

If he is getting 12.3V with car shut off, that means that battery is probably still good.

did you check the wires at the alternator for corrrosion, dirt, etc? It seems your battery is good

Originally Posted by Hrvat

If he is getting 12.3V with car shut off, that means that battery is probably still good.

Maybe, but if it's the original I see no harm in replacing for peace of mind.

It will take a few seconds after a start to register 14V on the cluster...you're fine there.

I also think something is loose or corroded...ground, battery cable, cable under the +terminal under the hood.

But, tell him if the battery light flashes again and increases its frequency until it's on all the time, that he needs to get home right away because he's driving on battery alone.

HTH

Those symptoms could also be attributed to a bad wheel speed sensor and the known taillight grounding issues.

Going back to when I worked for GM, there was a series of diodes in the alternator called a diode trio.
This was responsible for turning the battery light on. It was not all that uncommon for these diodes to fail.
In other words, the entire charging system was working properly, but the battery light would come on.
Not saying this is the case with yours or that it even applies to our vehicles. BTW, the diode trio was not
serviceable separately.

An E46 alternator shouldn't be troubled by turning on all the accessories, nor charging the battery after starting the car(the jump to 14.0 volts should take less than a second). The battery looks relatively healthy by the voltage it provides without the engine running, but the varying alternator output seems off. I'd look into fixing the alternator and getting a solid 14.0 volts before looking into the rest, since everything else mentioned will be negatively affected by a reduced output alternator.

I put a remanned bosch alt in just last weekend. I'm getting 13.8-.9...rarely do I see 14v

I'd start confirming connections, corrosion, etc before replacing anything. But the bosch remanned now is interchangeable with the valeo alt if that's what you have...so now you don't have to worry about what alt you have as much.

The numbers looked normal to me except that the alternator should not need to take time to reach its max 14.1V, but don't just assume that the alternator is bad yet, it could be either one, a weak or bad battery could also load down your alternator charging voltage to 13.7v with heater and lights on.

The easier way and proper way to troubleshoot the problem is to external recharge the battery overnight or even consider borrowing a known good battery and test it out, from there you can pin point weather the problem is the alternator or the battery, thus save you time and money.

Originally Posted by dmax

It will take a few seconds after a start to register 14V on the cluster...you're fine there.

I also think something is loose or corroded...ground, battery cable, cable under the +terminal under the hood.

But, tell him if the battery light flashes again and increases its frequency until it's on all the time, that he needs to get home right away because he's driving on battery alone.

HTH

Will check all connections over the weekend

Originally Posted by lcoleman

Those symptoms could also be attributed to a bad wheel speed sensor and the known taillight grounding issues.

I fixed his tail light grounding issue a few weeks ago, problem was there before and after. Wheel speed sensors don't trigger a fault code?

Originally Posted by mkodama

An E46 alternator shouldn't be troubled by turning on all the accessories, nor charging the battery after starting the car(the jump to 14.0 volts should take less than a second). The battery looks relatively healthy by the voltage it provides without the engine running, but the varying alternator output seems off. I'd look into fixing the alternator and getting a solid 14.0 volts before looking into the rest, since everything else mentioned will be negatively affected by a reduced output alternator.

Takes a good 10-12seconds to go from 12.5v to 14v

Originally Posted by taibinhvuong

The numbers looked normal to me except that the alternator should not need to take time to reach its max 14.1V, but don't just assume that the alternator is bad yet, it could be either one, a weak or bad battery could also load down your alternator charging voltage to 13.7v with heater and lights on.

The easier way and proper way to troubleshoot the problem is to external recharge the battery overnight or even consider borrowing a known good battery and test it out, from there you can pin point weather the problem is the alternator or the battery, thus save you time and money.

Cheers! will come back with the findings

That 10 secs. to jump to 14V is much longer than mine. Miles said less than a second...I thought a few secs...Miles is probably closer to the truth.

Look for corrosion/looseness...

Follow the cables all around...and if you haven't done so, you can easily get to back of alt by removing airbox...I'm sure you know. Clean the connector on the plug and check that cable connection under the alt's rubber boot...you might also see whether you have a collection of leaves in the vent tube too while you're there...or blow out the back of the alt (I found a crap in mine when I replaced it)

****, my alternator only reaches 13 volts...I hate it when I find out something is not right with my car.

Small update.. we noticed that when the DSC/ABS lights flicker, voltage reading jumps to 18v !! Warning lights stop flickering when voltage returns to 14v

Sent from my GT-I9300 using Bimmer App

Originally Posted by WDE46

****, my alternator only reaches 13 volts...I hate it when I find out something is not right with my car.

Very easy repair...and now bosch makes an alt that interchanges with a valeo, if that's what you happen have. I did, but the bosch fit fine.

Get that taken care of...you could just do the voltage regulator and hope that does it. The bearings on alts seem to last a while. Mine just failed last week and it was original.