Thread: Battery Light coming on - Charing or Ground Issue?

So the GS I've had for about 8 months. When I bought the car, the battery had died and the seller jumped the car, got it running, and I drove it home the next day. Everything seemed fine. I can't remember when it started, but one day the battery light came on. Checked voltage and it was fine, car ran and drove fine, so I drove it. The light only comes on when I am sitting at idle for a minute or two. Some days I can drive it on my daily commute of 100 miles round trip without it coming on. If I get a long red light, the battery light pops on.

So I had the local parts store check it. First thing they checked was the battery and they said it was bad. No biggie after sitting dead for a couple months, that is to be expected. So I changed it out with the one from my truck. Battery light still comes on. So I figure alternator. Get another one and changed it out. Battery light still comes on. On a cold start I am getting 14.5V. Both batteries hold over 12.8V when turned off for over a week. Warm idle the voltage does drop some, but never below 13.5V, on either alternator.

I checked the connections to the battery. They are clean and tight. I checked all the grounds under the hood and they looked good. Just for good measure, I cleaned the paint off down to bare metal, wire brushed the bolts, and reinstalled. Still the same issue with the light coming on.

So next thing, the engine to body ground is tiny IMO. And the alternator uses that as its ground back to the battery to charge. So I installed a larger 4 ga wire from the engine bolt to the body for a better grounding of the engine/alternator. Still get the light.

Today, I plan on picking up a 1 amp diode to increase the alternator output as suggested by ZZP in their tech articles. I could buy their Stage 1 alternator rewire, but I can solder, so I'll save my $15 and do it myself. Hope this works.

So where should I turn next? As I said, the car starts, runs, and drives just fine. Just the annoying light comes on. What else can I check or do?

You mention the small engine to body ground. I assume you are talking about the body to battery cable ground. The neg battery cable goes to the trans to engine stud and shouldn't be an issue.

Not sure if I can get it tonight, but I'll try and post a pic of the circuit.

Originally Posted by BillBoost37

You mention the small engine to body ground. I assume you are talking about the body to battery cable ground. The neg battery cable goes to the trans to engine stud and shouldn't be an issue.

Not sure if I can get it tonight, but I'll try and post a pic of the circuit.

Yeah, the wire is only like 10ga. Or at least from the looks of it. And its like 6' long. But I had read about upgrading the engine to body ground as part of the Big 3 Upgrades that a lot of audiophiles do. It was just a shot to see if it helped, which it didn't.

Ok, you've done the battery cables and looked under the boots for corrosion. Checked that the bolts into the battery snug down well. Upgraded a ground or two, cleaned the others. Changed battery and alt.

Have you checked the connector at the alt? IIRC one of the wires going into the alt to the regulator causes the light to pop on based on grounding etc. Might be a short or break in that wire.

Originally Posted by BillBoost37

Ok, you've done the battery cables and looked under the boots for corrosion. Checked that the bolts into the battery snug down well. Upgraded a ground or two, cleaned the others. Changed battery and alt.

Yes. Yes. Yes. Yes.

Have you checked the connector at the alt? IIRC one of the wires going into the alt to the regulator causes the light to pop on based on grounding etc. Might be a short or break in that wire.

I'm assuming you mean the plug in the back? That controls when the alternator is charging or not? No, I haven't checked that. Like I mentioned, I am planning to install the diode to increase the charging voltage, so I will inspect those wires this week when I do that.

That's the connector that the light is located on TMK. On our three wire setups one should be F or field to turn on the alternator to charge, S for Sense which is where you add the diode to fool the alt into thinking the power is lower than it actually sees, and L for Light...this is likely your problem wire/connection. IIRC when the regulator goes out, it grounds this wire. Or I'm just thinking that because it's Monday, and intelligence and Monday's aren't exactly best friends.

Originally Posted by BillBoost37

That's the connector that the light is located on TMK. On our three wire setups one should be F or field to turn on the alternator to charge, S for Sense which is where you add the diode to fool the alt into thinking the power is lower than it actually sees, and L for Light...this is likely your problem wire/connection. IIRC when the regulator goes out, it grounds this wire. Or I'm just thinking that because it's Monday, and intelligence and Monday's aren't exactly best friends.

What puzzles me is that the light doesn't come on all the time. It only comes on when I'm sitting at idle for a couple minutes. A couple weeks ago, we drove 400 miles to VA and back and the light never came on once because it was all highway.

I will check those wires, but I would think a broken or grounded wire would exhibit different symptoms.

Me too...

You stated that you replaced/fixed everything that should be causing the issue. All you left were a few distant straws to grasp at.

Here is the schematic for the charging system that I think you were going to post bill:



And reading up in the manual I found this about the operation of the light:

Circuit Description

The generator provides voltage to operate the vehicle's electrical system and to charge its battery. A magnetic field is created when current flows through the rotor. This field rotates as the rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC by the rectifier bridge and is supplied to the electrical system at the battery terminal.

When the engine is running, the generator turn-on signal is sent to the generator from the PCM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives battery positive voltage that is Hot At All Times through the GEN fuse in the rear fuse block. This voltage is used by the regulator as the reference for system voltage control.

Charging System Indicator

The IPC illuminates the charge indicator in the message center when the following occurs:
• The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the PCM requesting illumination.
• The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the body control module (BCM) indicating the system voltage.
• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.
• The ignition is ON, with the engine OFF.

So I will have to check the body grounds under the carpet and under the dash as well. I haven't checked them. I only checked the grounds under the hood.

Hmmm if you never have a voltage problem. Involve a BCM and PCM...oh nice. lol

Yeah Bill, the more I think about it the more I am leaning towards the BCM or Instrument Panel.

I am assuming the PCM is reading the correct voltage because I can scan that and see the voltage never drops below 13.5V, and I can also verify that with a DMM on the battery as it idles. So that leaves the Instrument Panel and BCM. The panel gets the voltage directly from the BCM. So either a bad ground at the BCM, instrument panel, faulty wiring between the two, or either of the units themselves are bad. Being that it is only happening when I am sitting at idle for a couple minutes, when the RPMs do drop down and voltage gets a touch lower, I am going to guess a bad ground or bad units, otherwise I would be getting the light intermittently I would think.

Thoughts?

Your idle will be lowest in gear with the engine up to temp. Just a little food for thought, typically when we test it's in Park. Since the voltage isn't dropping, that leads you to start speculating at the BCM/IP. The IP is more common from what I've seen than the BCM.

FWIW I have flipped a few Regals and once pickued up a 98 where the woman told me, "It's possessed and the gauges work backwards" Upon getting it running the low oil pressure light was blinking, the temp was indeed reading backwards and overall many issues. A simple cluster swap and the car was great. Oil pressure tested at 70psi with a mechanical gauge.

So the light in the instrument cluster receive the voltage directly instead of just a digital signal from the BCM? I've had my instrument panel apart to re-solder the Information Display chips because it was very dim. Hopefully that's all that's needed for this as well because of bad contact.

From the schematic etc...I'd be surprised if this is a loose/cooked resistor.

Just an update, I added the voltage booster diode last night and no change. Light still comes on.

I'm think about finding the pinout for the cluster and measuring the voltage supplied to the cluster to see if that changes at all. If it does, then I trace back. If not, the cluster is bad.

Thoughts?

Very logical. However you'd want the BCM wouldn't you. The above blurb you posted says the pcm or bcm through a class 2 can illuminate.

Originally Posted by BillBoost37

Very logical. However you'd want the BCM wouldn't you. The above blurb you posted says the pcm or bcm through a class 2 can illuminate.

Yup, you are right. I was just trying to eliminate one thing. And I know I can start the car w/o the IP, so that was easy to do. Hmm, back to thinking.

**SMACK**
Ouch..it hurts when I hit myself like that..

Originally Posted by rocknnachos

Have you checked for DTC's?

Yes, I have zero DTC.

Just as an update. Over the weekend, I swapped out a spare PCM with a stock bin on it and no change. Light still comes on. Again, just trying to eliminate things without tearing into it too far.