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Charging system headscratcher

9K views 5 replies 3 participants last post by  ggevaert 
#1 ·
Hello,


I have a 2006 charger w/3.5L. The charging indicator went on the other day so I started to investigate. With car running the measurement across the battery terminals was 11.9 and not the expected above 13 volts. So I thought defective Alternator. (the battery is only 6 months old and was installed by the dealer so I'm going to assume its the correct one for the car)

Bought and Installed a new alternator today and same issue. Bench tested the old alternator and it shows as being ok so looks like the issue never was the Alternator.

I did read that the ambient air temp sensor can cause this problem if it is not working; I'm going to test that out shortly but the temperature indicator in the dash shows the correct external temp so I'm thinking it will be ok.

I'm stumped, any thoughts on what could be the issue or what to check next?

Thank You.
Gary. :smile2:
 
#2 ·
Correction, it is the Inlet air temperature sensor; not the ambient air temperature one. I removed it and tested both it and the connection wire and both are fine. so, back to square one.

Next, read some articles that pointed me to the voltage regulator; which, unfortunately, is part of the PCM. Now I'm looking for a way to test to see if it is the voltage regulator and I found some info to do a Full Field Test but not sure yet how to do that on my car.

Stay tuned.
Gary
 
#3 ·
If this is a Mopar brand battery, I had one installed by the dealer in spring 2014, it was replaced under warranty Feb of 2015, failing to start. In March 2016, it again would not start the car, and I bought a battery tender/minder. After about 27 hours, it popped up and said the battery had a bad cell. Pulled the battery, hauled it back to the dealer. They tested it and charged it, said it was fine. Installed it back in the car and it started for about 3 days, then completely died. Battery minder again showed bad cell after abut 30 hours of testing and reconditioning. Replaced the Mopar battery with one from Advanced Auto, no issues since.
YMMV.
 
#4 · (Edited)
Bad battery

I don't have any problem starting the car, I'm just getting a lower and lower charge in the battery as I keep testing things out. I'm going to charge the battery tonight using my external battery charger so I can do tests with a full battery. My battery charger will tell me if a battery is bad (not sure if it will tell me if only a cell or two is bad).


Would having a bad battery not still show the higher voltage from a working alternator when measured across the neg/pos connections?

Also, determined that a full field test has to be done by the dealer (in newer cars where the computer connects to the alternator) or serious damage to the computer can occur.


Gary
 
#5 ·
I don't have any problem starting the car, I'm just getting a lower and lower charge in the battery as I keep testing things out.
Keep it simple, don't make any assumptions. If the battery's charge is less than expected, and there is no CEL or DTC about charging system, the problem is either the alternator's output (alt going bad) or the wiring/connections between the alternator and battery isn't up to snuff. You should be able to determine which is at fault by using a hand-held multi-meter (the $5 el-cheapo model from Harbor Freight will do just fine if you don't already have such a tool).

1) With the vehicle running and in closed-looped operation (warmed up fully), test the alternator by placing the multi-meter + probe on the alt's + post and grounding on body ground post below shock hat.

2) If that test passed, the alternator is doing what it is supposed to be doing, so the problem has to be with the wiring going to battery or one the connections therein. Remove cables from battery, clean, reinstall, and check alternator charging numbers again. Compare to original numbers. If they aren't the same, there's a bad cable or connection at battery.



I'm going to charge the battery tonight using my external battery charger so I can do tests with a full battery.
It is good to start with a fully charged battery here, but not absolutely necessary given the condition that you're troubleshooting.

My battery charger will tell me if a battery is bad (not sure if it will tell me if only a cell or two is bad).
Be careful with that assumption. Yes, some battery chargers have that ability, but if yours is just one of the standard models available at a local hardware store/auto parts store, it cannot adequately test the health of the battery's internal cells. However, since you say there is no issue with starting the car, that means the battery's cells are currently in good health and you don't necessarily have to test those further.

Would having a bad battery not still show the higher voltage from a working alternator when measured across the neg/pos connections?
Any time you are testing voltages at the battery itself, you need to be mindful of what you are actually touching with the probes while testing.

1) If your probes are touching the connections and not the posts, you are only testing the voltages coming through the wires.

2) If you are touching the posts instead of the cables' connections, you are only testing the voltages making it into the battery, not the voltages being sent to the battery.

Usually there should be no difference in those two numbers, but if the cables' connections are dirty, loose, or otherwise not up to snuff, there will definitely be a difference. I don't want to put too fine of a point on all that, but it is important to be mindful of lest you misdiagnose something simple as something requiring a more complicated (read: expensive) fix.



Also, determined that a full field test has to be done by the dealer (in newer cars where the computer connects to the alternator) or serious damage to the computer can occur.

Gary
That's what they say, and while technically accurate, it makes it sound a lot more involved than it really needs to be. Allow me to translate: don't slam a six-pack of beer before applying 1970s-era troubleshooting techniques to a car which was manufactured in the last 10 years.

I'm just as guilty of doing that as anyone, and to be fair, it worked for us for so long, you can't blame us for trying to continue to use the same process with our cars today. But nowadays the car's PCM monitors the car's electrical system and determines its power needs in real-time, continually adjusting the alternator's output to maximize its charging output while making sure it doesn't put out more than is needed or can be used. And because of that, any errant electricity spikes in the charging system, such as from a shade tree mechanic trying to test the system but doing so incorrectly, could end up damaging the car's PCM.

Having said that, if you make sure you know what you are doing and what you are expecting to see with each test, you should be able to avoid bricking your car's PCM. After all, it's not rocket science ;)
 
#6 ·
Resolved!!

Thank You for that information GertFrobe. Very useful.


So, the issue has been resolved. It turned out that the new alternator I installed (purchased from Canadian tire store - equivalent to Autozone) was bad. it was a Remy ACdelco model so I typically expect good quality from them so I didn't bench test it before I put it in but this one had something wrong with it.


I ended up taking my old alternator to a company who specializes in alternators and they indicated that my voltmeter test only tests the diodes (so it showed as good when it was not) and what actually happened was that my rectifier fried but not all the diodes (which, according to them, is rather unusual). They fixed it up (for half the price of a new one) and everything is now back all good.


Their thought, on the odd situation where my rectifier is fried but not all the diodes, is that someone boosted the car and they either did that wrong or it went bad. Since no one (that I know) boosted my car since the battery died 6 months ago they feel that it could have started back then and slowly worsened. It could have also been the battery failing that could have caused the issue.


Either way, lesson learned is to have a professional company check the old alternator out.


Thanks to everyone for their help. I learned a lot about my car's charging system so it was a good learning experience. :grin2:


Gary
 
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