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Battery not charging 2002 Sonata 2.4L

19K views 28 replies 6 participants last post by  AUTOSPARK 
#1 · (Edited)
Looking for a few ideas on where to go here.
Car starts and runs fine, then it dies and battery is dead after 15 minutes.
Battery is new and load tested good at 2 different shops.
Alternator is replaced and new, both alternators load tested good at 2 different shops.
Battery voltage is 12.4V while running, as I turn on lights and A/C it drops to 11.84V.
Battery voltage then continues to drop while running, 11.83V, 11.36V, 10.98V and gets around 10V and car dies.
I do not have the 14.5 volts from the alternator on the battery while running which I think the alternator puts out to charge the battery.
So I guess what controls the alternator charging? What tells it to turn on and off?
I have no codes so am stumped.
All fuses and relays check out good. Replaced battery terminals. Wires look good.
Also battery does not drain or loose voltage while sitting.
Thanks for any help, this was my welcome home present after heart surgery. "Honey the car died lol".
 
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#3 ·
It's has a battery light. The battery light comes on when you first turn the key to on. And then it goes out when the vehicle starts and runs for awhile.
The battery light then comes back on when it dies and will not start. "It just clicks till I recharge my battery".
I have a new Innova Scanner and it does not show a code. The scanner does work.
 
#5 ·
If the battery sits for a few days it stays at 12.4V, there appears to be no draining when car is off and unused. My thinking is something reads and tells the alternator to turn on and charge the battery and then shut off when its upper limit is reached while its running. I would think something has to control the alternator and the charging. Would it be the ECM?
 
#6 ·
When cars were still mostly mechanic the charge light was used to feed 12V from battery to excite the alternator so it would start charging (and subsequently the light goes off). Therefore the charge light used to have a bigger bulb (3W) than the other ones in the cluster (1-1.5W)

The setup on the Hyundais appears to be a little different, there's the light (dash bulb of same size as the other ones) plus some pre-excitation resistor (with a diode, located in the passenger compartment junction box if you can believe Haynes ...) in the drawings.

How did the shops determine the alternator is good ?
 
#7 ·
Optic, you need to carry out a volts drop test on the alternator wiring. It's usually quite easy to do depending on how accessable the alternator is on your engine.

Connect your voltmeter red lead to the main B+ post on the back of the alternator and the black lead to the battery positive terminal. Now start the engine and run it at about 1800-2000RPM. Now switch on your headlamps, heater blower, etc and see what voltage you get on the meter. The reading should be less than 0.5Volts.

If that checks OK, switch everything back off and move the meter to the return (ground) side of the circuit, so meter balck lead to the alternator casing and the red lead to the battery negative terminal. Run the engine as above and switch on the headlamps, blower, etc and check the voltage on meter. You're looking for less than 0.5V again.

If either one (or both) of your readings is over 0.5V then you have a high resistance in the alternator wiring. Having said that, with the voltage readings you've posted it sounds like something is completely open circuit (a very high resistance). Volts drop testing is the best tool to use to find out where the fault lies.

Let us know what you find.

Scott.
 
#8 ·
I took the Battery and Alternator to AutoZone and O'Reilly auto parts and they tested them about 5 times each. Both passed well within ranges. I can go out right now and the car runs great and lights are bright everything seems fine. My fluke meter shows the 12.4 on the battery while it's running and also shows the same disconnected. I shut it off and it fires right up. I can drive to store fine. When I am heading down my road back home everything seems to go out like it's losing power. If I let it sit for a bit in the drive it dies and will not start and the battery is dead. If I charge it, I'm back running again.

Here is what is throwing me off. I'm a long time network engineer until I got sick, so I understand electronics. My dodge ram 2500 had the same problem, exactly, drove me nuts. Replaced battery and the alternator and it would not charge. Finally someone said the PCM controls the charging. I sent the PCM to Georgia and it was rebuilt and I put it in and truck fired right up and charged fine. No problems since. So does the Sonata PCM control this charging? This is something sticking in my mind because of the Ram lol. The 4 wire plug that's on the alternator is that for the idiot lights or is it a PCM control? I was up at Speck Hyundai with a salesman and we walked into the service department and I asked the guy what runs the charging after the Alternator and Battery, he said the PCM, and that was all he offered. So now im thinking oh crap just like the Ram.

Tomorrow I will try to trace out the wiring and load test as you suggest AutoSpark. I will keep this updated and post a result for all to see. I hate people who fight tough problems and when its fixed the result is not posted. And thanks e3tom, any suggestion helps.

Hey guys, thank you so much for trying to help I really do appreciate it tremendously.
Scott
 
#9 ·
All alternators need a strong 12 volt low amperage feed from battery for the field windings, to put out the rated approx 90 amp to run the whole car.

It's normally a small gauge wire , unlike the single large red feed coming out to the battery.

This feed I believe often has a fusible link in line some where. It's sometimes called the trigger wire.

Use your multi meter to confirm one of the four small wires on the plug is the same or very close to full battery voltage ie 12.4 volts. If it's only 9 or 10 volts you have found the problem; follow the feed back and find a green corroded connection or bad fusible link.
Good luck.
 
#10 · (Edited)
Speaking of Santa man it's cold n windy out lol. Ok I will go under car tomorrow and see if I have the 12V trigger voltage on those field terminals. Thanks for that tip Santa.

Well I couldn't resist so I went out and checked the voltage drop as Autospark suggested. Interesting result. the Ohm test had 0.2V so that seems correct. I did the volt test and it read 5.5V at idle and when I revved it up it went to 6.5V. So I guess that's bad. Will have to check for a 12V trigger tomorrow on the 4 wire connector.

Is the 5.5V feed back? Does the Main B+ 12V wire run directly to the battery? I tested the 120V fusible link again and it's still fine. Since I didn't have a hand I put my big jumper cable on the battery and connected one end to my meter and the other to the B+ and reversed it for the Ohm test. I hope there is not that big of resistance in the big jumper wire to to give me that increased voltage I see at the B+ as 5.5V. It shouldn't since that looks like a 4 gauge wire maybe.

Thanks guys, watch this be something dumb like a cruddy wire. I would think that would be intermittent though so I'm going to find and clean all connections.
 
#14 ·
the Ohm test had 0.2V so that seems correct. I did the volt test and it read 5.5V at idle and when I revved it up it went to 6.5V. So I guess that's bad.
I'm not sure what you tested here. Ohm test & volt test?

What was your meter connected to when you got 5.5-6.5Volts?
If your getting volts drop like that on the tests I suggested, then don't bother pissin' about with trigger wires, field wires or anything like that. You've already found what is causing problem...high resistance. Next you need to narrow down where the resistance is.

Scott.
 
#11 ·
Yeah it's warmer in Alaska lately than it is here down south, go figure.

With car running and a few options turned on, voltage across battery terminals should be between 13.5-14, like everyone said.
Two different alternators not likely bad or tested incorrectly; problem likely lies with wire harness feeding alternator.

Unhook the plug at alternator and using meter find out which is the positive feed coming in from battery. Has to be close to battery voltage, not missing much, at the most one volt drop down from what battery is.

Clean/polish up all connections with emery paper etc, copper should shine.
 
#15 ·
AUTOSPARK my test was:
The voltmeter was connected (B+) alternator to the Pos.+ on battery gave me 5.6V (900 rpm) to 6.5V (2000 rpm)

Voltmeter connected Alt. casing (gnd) to battery neg (-) gave me .02V

Alternator Computer Report listed as:
Turn On Speed 1238 RPM
Regulator Activation Speed 1238 RPM
Voltage Set Point 14.4V
Maximum Output 113 Amps
Secondary Regulation 15.5V
Feedback Minimum Load 10.2V

Thanks Scott
 
#17 ·
Very confusing as to how you are conducting this voltage test. Could you place your black(negative lead of your voltmeter) to the negative post of the battery and then the other lead(usually red) on to the positive post of the battery and get a voltage reading. Keeping the black lead where it is on the negative battery post, put the red lead to the output of the alternator and get a second voltage reading. The difference between these two readings is how much drop you have from the alternator to the battery. You can do this test at various engine speeds to get an idea of how your alternator is doing. Not trying to sound condescending, just not sure how much experience you have with a volt/ohm meter.
 
#16 · (Edited)
Alternator Connector Wiring and Voltages with connector unplugged and car running.
Blue 0.2V
Orange 11.86V
Gray 11.4V
Pink 11.1V
B+ N/A

I'm stumped now lol, that makes it look like alternators bad.
I am going to put connector on and start car and crawl under there and measure voltages.
 
#18 ·
DVOM... black test lead at battery post.. positive lead at battery positive with engine running.. what voltage ??

Move positive lead to post at rear of alternator.. what voltage we have there (running)??
 
#19 ·
OK GUYS, lets say I have extremely minor experience with a meter lol. I guess we can have fun with this. And sorry Johnauld i just cut through the chase I guess and dont worry I never get offended.
My voltage drop was 5.5V on the POSITVE side of the alternator.
On the GROUND side it was 0.2V
I did the test AutoSpark suggested and its the same test Autozone have on their website for alternators. I even dragged out my Innova meter that does load testing but figured it would never put enough draw on that battery lol.
You wanna knows whats become comical around my friends, I was a navy crypto tech on the CNO's crypto team in the pentagon, I then went to DEC, Honeywell and Computervison. Was sub-contracting for IBM, then after 12 years with Charter Comm I still can't fix a **** 12V Sonata lol.
 
#22 · (Edited)
Thanks man, i found the Sonata schematic also, so I know where i'm at and what's what on that plug. I can trace it out quick now. Oh Joy, the service guy was right and the PCM is involved lol.

I will let you know what I find, if the PCM causes this like it did in my Ram i'm gonna be ticked lol, at least $99 bucks rebuilt sure beats a dealers $1200.
BTW I ohm'd the fuse out when i took it out but did not do a voltage drop test. So if that's it, nice call.

Sorry about my lingo lol, i'm more used to data and long haul fiber, dont know crap about cars. Had someone else fix em when I had a job haha. After this is done I got the air bag light, that will probably blow up in my face :)
 

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#23 ·
Oh Joy, the service guy was right and the PCM is involved
Yeah, the PCM is indirectly involved in the charging circuit, but you don't need to concern yourself with that side of things. That's a completely separate circuit and your volts drop test seems to suggest that that circuit is OK because the voltage drop increased when you revved the engine. That tells us that the alternator was trying to push more current to the battery...so it's charging. Remember Ohm's law tells us that the voltage drop across a resistance is proportional to the current passing through it.

I knew that Ohm's law stuff would come in useful one day:laugh:
 
#26 ·
Thanks Autospark, the battery to alternator cable was indeed bad. I had to reach around inside because they routed it funny around and through the motor and feeling for worn spots "I couldn't actually see the cable", next thing you know this corroded cable was falling apart in my hand. Actually was working at one point then got it to crap out again by pulling on it, I will replace it tomorrow and should be good to go.
 
#28 ·
Well I installed new cable and it run's fine. Looking from the bottom laying on your back the cable looked fine so honestly I really didn't even consider it, my bad. But as I was doing the voltage drop tests I pulled on it more to get my meter on it better. As soon as i did that, the whole connector started coming out of the insulation and nothing but green around the wires and I was amazed at how the wires were just shredding from under the insulation as I pulled on the cable. So for now we are good.
Thanks Guys.
 
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