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 Post subject: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 2:27 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8118
Location: Baltimore, MD
Ok - first off let me say I've been trying to troubleshoot this issue for a few days now and it's been driving me nuts. On Friday, the battery light came on in my instrument cluster with the statement "Battery Not Charging". I figured the alternator was probably on its way out since it was the original with 156,000 miles under its belt. I tested the output of the original alternator and my suspicions were confirmed - it was only putting out 10.1 volts. Revving the engine brought it up to only 10.4 volts, which is still too low.

I replaced the alternator. When I was done, I measured the output of the new one at exactly 14 volts. Much better. I started the truck and all seemed well for about the first 30 seconds. Then, the battery light came back on and I got the same message. I measured the output voltage again and it was still the same. The voltage across the battery itself measured just under 12 volts (11.93 according to my notes). After a couple more starts, the voltage on the battery started to drain and it wasn't increasing while the engine was running. I pulled the battery and took it to one of my neighborhood parts stores for testing (the battery was about 5 years old). The tester showed that one of the cells tested bad. So I get a new battery and install it.

The same thing kept happening. The next thing I figure is a broken wire or bad/corroded connection somewhere. I clean the cable connectors at the battery and at the plastic junction box where the + wire from the alternator connects to the + battery cable. I also measured the continuity of the + wire from the battery connector to the terminal on the alternator. It had good continuity. I did the same thing for the - battery cable to the engine block. Continuity was good.

I feel like I'm going nuts now. The best I can tell, I have been all through the charging circuit and I can't find out why the battery isn't charging unless there's something I'm missing somewhere.

Anyone been down this road before?

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 2:42 am 
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Joined: Jan Mon 17, 2011 8:57 pm
Posts: 571
Worn/slipping/loose belt?
Dirty/loose connections at alternator itself?

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 3:21 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8118
Location: Baltimore, MD
EICOKnight wrote:
Worn/slipping/loose belt?
Dirty/loose connections at alternator itself?


The belt isn't cracked, frayed, and doesn't seem to have any slop in it. I put it on about 30k miles ago.

I used a little DeOxit on the wiring harness that clips to the back of the alternator. The lead going to the battery cable junction box is clean and secure.

Thanks for the suggestions. If there's any others, I'm all ears!

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 3:32 am 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 4825
My previous and current GM pickups are diesel powered and the alternator is under control of the ECM, I assume the gas versions are the same. Check the wiring from the PCM to the alternator, there are probably two small wires in a connector.

Rodger WQ9E


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 3:33 am 
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Posts: 11544
Location: S. Dartmouth MA 02748-1225 USA
New, defective alternator.

Assume no ammeter, measure the resistance of the charging cable from the alternator to the nearest connection, note... Run the engine at fast idle and measure the voltage from the point on the alternator resistance was measured to the other point, voltage drop. Ohms law will yield the amps charging, or not... Expect the voltage drop to be very small usually mili-volts, so a solid connection to measured points essential.

If there is charging and still a warning then there may be a problem with the ECU port or the "sensor" in the alternator.

GL

Chas


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 4:02 am 
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Joined: Oct Thu 20, 2016 3:54 am
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Location: Missoula mt
In a lot of new rigs the volt reg for the alt is in the ecm....big bucks... check the field excitation of the new alt.....WA7OPY


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 4:13 am 
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Posts: 9683
Location: Redlands CA
It's not unheard of for rebuilt alternators to take a dump, particularly if you install it and run it against a dead battery.

It most likely is controlled by the PCM. and on a ten year newer Tahoe I've had the PCM shut down the Alternator in such a case to protect it from overload.

It set a code that had to be manually cleared to turn off the charge light. I don't think a 2004 has that level of control but if you have a code reader it might not hurt to clear the codes, even if the battery was disconnected.

It wouldn't hurt to check all the fuses, I don't think the field is fused since it's controlled by the PCM but can't hurt to check.

If you haven't figured it out by tomorrow I can look up the schematic and possibly offer another suggestion.


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 6:24 am 
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Location: Santa Cruz mountains
I replaced the alternator in my BMW about a year ago. Same situation as you, the light came on all of a sudden. Even with all accessories off, I barely made it home.

The alternator that came with my car was made by BOSCH. I replaced it with an identical NEW alternator.

In the instruction sheet that came with it, there was a number of HUGE admonishments and thou-shalt-nots in various places about installing the alternator and attempting to start the car on a less than fully charged battery. They wanted the battery to be almost 14 volts before starting-anything less risked damage to the alternator. I took this to heart, and used one of my other cars to charge the battery for almost two hours before the first start. Everything went off without a hitch, and the alternator has performed flawlessly.

Perhaps the problems with your unit has to do with your old battery. 11.93 volts is VERY low for a car battery.

While I was comparing prices, I was astounded at the poor quality of the aftermarket alternators available. Almost all of them really sucked, with marginal current sourcing at best. Most of them required removing the pulley of the old alternator, which wasn't going to happen.

I still have the old alternator. Supposedly, I can buy the voltage regulator/brush assembly as a separate piece and get it working again for about $50.00. I'm seriously considering it so I'll have a spare.


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 3:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8118
Location: Baltimore, MD
The output of the new alt is measuring at 14.1 volts at idle, so it seems to be good. It's a Delphi, which is what the OEM was. I would think if it were an ECM problem the output of the new alternator would be squirrely or low. I'm going to do some more troubleshooting this evening and will report back with the results.

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 4:50 pm 
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Joined: May Sat 06, 2006 4:03 am
Posts: 2817
Location: ZIP 23831 South of Richmond, VA 25 miles down the pike.
From experience. If battery and alternator ok I think you most likely have a bad highly corroded cable and/or engine block connector. Corrosion is the resistance blocking current. All that time it builds up inside cable and very much where connector goes. If you have some slack you might could cut off some of the cable end with connector and get back in business. Or replace cable.

Bill J.


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Wed 06, 2017 4:57 pm 
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Joined: Dec Tue 01, 2015 5:31 am
Posts: 605
Location: Columbus Ohio
Check the main relays up in the engine compartment. You can swap the starter relay with another there to test,
but I'd just replace them both, maybe 3 there. I experienced a similar problem, the starter relay was my bad part.

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 12:42 am 
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Joined: May Sat 30, 2015 11:49 pm
Posts: 128
Location: Keystone Heights, FL, USA
Meter set on D.C. Volts.
Red lead on alternator output post.
Black lead on battery positive surface behind the cable if possible (actually ON the battery positive)
Run engine and report voltage.

Engine running put black lead on alternator housing
Red lead on battery negative, right on the battery behind the cable if possible.
Results in volts?

OR

Engine running.
Measure voltage from alternator output (red) to alternator housing (black) Be careful don't tangle lead in fan.

Then measure voltage at battery.
Results?

Jeff


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 1:53 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8118
Location: Baltimore, MD
I cleaned the connections better today. Alternator output is 14.3 V at idle. When the engine is running, I'm getting an even 14V at the battery, so the power is getting there. Might be a tad low, but it should be enough. The warning light is still on the dash and it's still giving the "battery not charging" message. I borrowed an OBDII scanner and it threw back code P1637. I don't know if this code is a residual or not, as I learned when I changed out my O2 sensors a year ago the computer in this thing takes forever to reset on its own. I read somewhere that the GM computers can be finicky with an alternator swap - no idea if this is accurate or not.

Since the voltage from the alternator is good and the battery is getting the voltage it should be, I'm not too worried about the light. If the battery wasn't charging, it would be hard to start by now as many times as I've cycled it. I've driven it about 200 miles since I swapped in the new alternator and have not noticed any other issues.

If it doesn't go away in the next couple of days, I'll pull the alternator and take it for testing. I've heard of new alternators being bad or having poor performance out of the box.

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 2:06 am 
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Can you delete the bad codes with the borrowed scanner?


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 2:26 am 
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Joined: Oct Thu 20, 2016 3:54 am
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Location: Missoula mt
To reset the codes a lot of rigs just need to have the battery disconnected and then reinstalled....WA7OPY


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 3:01 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 8118
Location: Baltimore, MD
wa7opy wrote:
To reset the codes a lot of rigs just need to have the battery disconnected and then reinstalled....WA7OPY


This one isn't like that, unfortunately. When I changed out the O2 sensors, disconnecting the battery for an hour did nothing with the code. Had to drive it a few hundred miles and cycle it quite a few times.

The scanner I borrowed is a very basic one that doesn't seem to clear codes.

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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 3:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10973
Location: Mpls, Minnesota
The PCM controls both the charging and the light, suggest you have it scanned with a good scanner to determine what the problem is, if it was charging properly the light would be out.

Dave


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 3:59 am 
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Location: Redlands CA
The code is for the field wire from the PCM to the Alternator.
As I mentioned above you may need to clear the code
To get the charge light out.

If you clear it and it comes right back then you still have a problem, either the Alternator, the wiring or the PCM.


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 4:17 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10973
Location: Mpls, Minnesota
"P1637 Chevrolet Description: The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the Powertrain Control Module (PCM). The PCM applies ignition voltage to the generator L terminal circuit. A small amount of current flows from this circuit through the generator windings to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped. The PCM expects to detect low voltage on the L terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational."

Dave


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 Post subject: Re: 2004 Silverado battery not charging
PostPosted: Dec Thu 07, 2017 4:22 am 
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Joined: Jul Thu 29, 2010 5:35 am
Posts: 836
Location: Simonton, Texas
Do a voltage drop test on the negative terminal battery wire and the engine block.

Do a voltage drop test between the negative battery terminal and the chassis.

These tests should be done when cranking the engine to impose a high load on the circuit.

Do a voltage drop test between the positive battery terminal and the alternator plus terminal.

This test should be done withe engine running

There should not be over a one half volt drop between the 2 ends of the circuits.

Should there be over one half volt difference there is a resistance problem.

Hope this helps.

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