Intermittent battery light

[Mikealwa]

I'll read it, the noise went away, but volts reads good I'll check the ripple. I can't post videos but yeah it sounded like an old computer booting up amplified. If that makes sense.

[andrewwynn]

So in my case when first starting I would get a rattle that you could describe like marbles tumbling inside. Not a pleasant sound.


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[Mikealwa]

Battery light came back on same as before with the last alt lol. I'm assuming both alys were good. I changed the ignition switch last year hoping that would fix a flickering battery light, which was actually cause by my original bad alt. In a last ditch effort I put the old ignition switch in. Lights been off for two days, but I'll report back in a few days. Hope this magically ends this saga although not sure how that causes a battery light. Just saw a random YouTube video.

[andrewwynn]

Take scan with oscope after. If no lights and the signal has a small peak to peak maybe ignition switch was not staying closed on one of the terminal ckts. Plenty of times some seemingly unrelated error is the ignition switch.

[Mikealwa]

Alright you're probably sick if me haha, so lights back on, but new repeatable behavior...light goes on, but turning lights on and max ac (increasing load) turns it off and this is repeatable. Does that point to any direction? I have no issues starting the car ever, but could this 1 year old battery test good, but somehow cause issue. I did the ground test, engine block to b- post and tested good.

- - - Updated - - -

Rpm increase isn't turning the light off only turning on load, max ac and lights. Some days however light stays off

[Mikealwa]

A friend speculates higher load increase current which may overcome a corroded power wire somewhere. I recleaned the b post and smothered dialectic grease. Also the power wire to the starter was covered in oil. For now I sprayed it with electric cleaner. I'm going to do the transfer case and front diff fluid soon so when I drop the brace cover I can clean that better. I'll give the updates a rest until I find a solution!

[Henn28]

Idle automatically goes up a bit with the AC on. However, if your alternator had low output at idle, regardless of ac status, it should try to boost the idle due to the low voltage and the car should pop a code.

My throttle body plug partially unplugged due to old plastic breakage and the car started hunting for idle and would pop this code. The DME is smart enough to try to boost the idle RPM in order to get the alternator voltage back within limits. Seems too convenient that your idle goes up with the ac and the light goes out.

[Mikealwa]

The light goes off with AC on, but not when I give it gas. I can try to confirm next time the light goes on, but it's been off for three days now. I did finally get a foxwell I saw Andrew uses and I reset adaptations for fun. I had to recalibrate my throttle. I'm not sure if that's why the batt lights been off for three days or not. It's so random and inconsistent.

[andrewwynn]

You can graph battery voltage over time with the foxwell. If there are dips or spikes it's much easier to see with a graph.

[Mikealwa]

I don't see voltage on nt710 the list of live data, only like 20 things? I gotta figure it out. My cheap scanner has way more data, but can't graph, not sure what gives.

[andrewwynn]

You have to get to the sub menu pertaining to the data you're looking for. I'll see if I can find it I was going to hook up my foxwell soon anyhow to check on battery state of charge history.

[Mikealwa]

I appreciate it! So the light came on a gain for a bit and I did more testing with my other OBD2. While I did the testing the battery light stayed off. At idle with nothing running I'm at a constant 13.7-14 V. With AC on max, high beams, heated seats and steering wheel and rear defroster on I'm at 11.5, but the light is not illuminated. With all those accessories on and throttle at 2500 rpm I'm at 13V. Haha idk if this tells anything. My battery light stayed off for all these tests. Should voltage remain around 13+ no matter what accessories are running? Again my battery light only comes on when I have no accessories on and sometimes lol. This is weird. Battery has never gone dead or had trouble starting after a new alternator trying to fix this and months of this.

[andrewwynn]

Battery voltage is usually 13.6 ± 0.2 no matter three load conditions.

When the brushes wear out the field windings can't get enough current at low rpm to maintain voltage under load.

I'll help you find the voltage to graph it. If battery voltage can't stay constant you might have a bad ground or factory defect VR.

New ≠ fixed, plenty of cases of defective new part, but it does suck hard when it's intermittent.

I don't think the e53 shuts off the alternator like three e70 does.

[Henn28]

11.anything volts is definitely too low and the cause of your symptoms I think. I agree that a ground issue could be the cause, and is the easy place to start troubleshooting. Have you checked the obvious grounds? There are several under the floor in the back, Around the spare and the battery. Including a large one by the fuseable link box. I would first though check the big ground down on the front of the right frame rail. It’s under/near the ac compressor on the 4.4. Corrosion or an otherwise loose connection here can cause a lot of issues.

That said I do see too many posts about rebuilt alternators failing in short order, especially the Bosch units. So I think this could be high on the list too.