Intermittent Battery Light

[rc8419]

2002 330Ci 40k miles

Battery light has come on intermittently over the past couple of drives. Battery is only a few months old.

I looked at the battery terminals and notice this one circled is getting hot. Is that a factory cable?

Screenshot_20221120-160322_Photos.jpg


The PO had some crazy stereo system in the car and he took all that our before selling it. I tried to remove that cable but the 13mm nut in the photo is not budging. Might need some Kroil

[All2kool]

I looked at the battery terminals and notice this one circled is getting hot. Is that a factory cable?

Yes, that is a factory cable and it looks like it's been getting HOT for a while now. An intermittent Battery Light is likely a failing Alternator, which of course would happen if an audio system overtaxed it for long periods of time.

[rc8419]

Yes on the battery light usually being alternator related. But why should that connection to the battery be getting hot?

I can throw in an alternator. Just dont understand the other symptom.

Thanks!!

[All2kool]

Yes on the battery light usually being alternator related. But why should that connection to the battery be getting hot?

I can throw in an alternator. Just dont understand the other symptom.

Thanks!!

There is an OBC function that will tell you the voltage when the vehicle is running. If the Voltage Regulator on the Alternator is not functioning correctly, it could make the cable you mentioned get hot by not regulating the voltage correctly. The Voltage Regulator on the Alternator can be replaced separately but if your Alternator has more than 120k miles, I would just replace it. BMW sourced Alternators from Valeo and Bosch and they are not interchangeable. You can snap a pic of the back of your Alternator with your Smartphone to see which brand you would need.

[All2kool]

There is an OBC function that will tell you the voltage when the vehicle is running.

Anything above 14.5 volts would be BAD. Anything above 15 volts would be REALLY BAD.

[rc8419]

Car only has 40k miles on it, as mentioned previously. Very disappointing.

I will look and see what voltage is measured at the battery while car is running. Then check which model alternator I am likely replacing.

Thanks

[All2kool]

Car only has 40k miles on it, as mentioned previously. Very disappointing.

I will look and see what voltage is measured at the battery while car is running. Then check which model alternator I am likely replacing.

Thanks

Here's how you test to see voltages reported by the On Board Computer (OBC).
https://www.youtube.com/watch?v=X8yRXxxJ9To

[MarcoZandrini]

The cable is overheating, as previously cited. Excessive current causes overheating and not over-voltage. Yes, check the voltages, especially under the hood at the jump post (use the engine as the ground).

[E39 Newbie]

Car only has 40k miles on it, as mentioned previously. Very disappointing.

I will look and see what voltage is measured at the battery while car is running. Then check which model alternator I am likely replacing.

Thanks

Disappointing?? The car is over 20 years old. Stuff like this breaks even on low mileage cars.

As others have said, it's probably the alternator. I will quibble a tiny bit. The voltage regulators on the Bosch (easy to replace) and the Valeo (not sure if they're even replaceable or not) are different. However, the alternators, themselves, are identical. Others can chime in here, but I replaced my completely worn-out Valeo with a Bosch unit. I, too, was worried that they were not interchangeable. I dug through all the part numbers and interchange numbers and they all pointed back to the Bosch units.

[All2kool]

...but I replaced my completely worn-out Valeo with a Bosch unit. I, too, was worried that they were not interchangeable.

The reason they are not allegedly interchangeable is the plug; one being squared, one being rounded. And the pulley.

Alternator.jpg

[MIKYZZ4]

A most probable cause of a cable getting hot at the terminal is high resistance, which is usually caused by a bad connection at terminal or damaged-broken wiring at heat source location.
If the entire length of cable was hot enough to melt outer covering or worst the metal itself , that would point to a short.

[XnWarden]

I agree with the short circuit diagnosis. Find the ground locations for the circuit that cable supplies power to, and check them for corrosion. Then inspect the rest of the circuit for breaks in the wire.

Sent from my SM-G975U using Tapatalk

[E39 Newbie]

The reason they are not allegedly interchangeable is the plug; one being squared, one being rounded. And the pulley.

Alternator.jpg

I get it. But if you check the PNs in RealOEM, then check various parts sources, both the Valeo and Bosch have the same plug now. I note that in your pic both alternators are Bosch, although the one on the right is technically BMW. What car did the one on the right come out of? I tossed my old one or I could check it. The pulleys between the two are different, although the depth and diameter are the same.

[e464]

You have not told me if the cable is CURRENTLY HOT, or in the past life was HOT. Please test with back of fingers after driving.
Second, I use a plug-in voltage meter in the cigaret lighter hole to see current voltage.
If it does turn out to be the alternator, you can replace JUST THE VOLTAGE REGULATOR and rectifier for cheap like 1/6th the cost of a rebuilt. It takes a little time
to get the proper parts, but take the rear cover off and simple replace o components. Just a thought. You will have to wait a few days fr the parts to come in if this is a fun car.
Could be loose/damaged cables causing poor charge connection.