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2002 Mit. Galant Low Voltage (p1500)


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mat5153
New User

Aug 4, 2012, 6:49 PM

Post #1 of 7 (5298 views)
2002 Mit. Galant Low Voltage (p1500) Sign In

My 2002 Mitsubishi Galant 2.4 w/ 97,000 miles) has been intermittently experiencing low voltage across the battery. Every morning, (after the car has been sitting all night) the voltage across the battery is 14+. (Alternator is charging the battery) As I drive to work (and the engine warms up) the voltage gradually drops 13.9... 13.8.... 13.7.... When I start the car after work (after sitting in the sun and 90+ degree heat) the voltage across the battery is less than 12. (Alternator not charging the battery) It seems like the alternator will not charge if the car is warm (even just from a hot day). I have run the code scanner. I am getting a p1500. I have replaced the alternator and battery recently. I think the battery is good, but the alternator was cheap. I'm thinking I should replace the alternator with an OEM. Any other thoughts out there?? (especially regarding the p1500).

Thank you!!

Another side note... the charging system warning light does NOT come on while the car is running... maybe a short somewhere????


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(This post was edited by Hammer Time on Aug 4, 2012, 7:45 PM)


nickwarner
Veteran / Moderator
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Aug 6, 2012, 2:57 PM

Post #2 of 7 (5238 views)
Re: 2002 Mit. Galant Low Voltage (p1500) Sign In

Before you replace the alternator, have to load tested on the car to verify its output is within spec. If it is the OE one won't do anything but drain your wallet. Have you checked for voltage drop on the field coil terminal and the main power to battery cable? If you are unfamiliar with a voltage drop test I can explain it to you pretty easily. It doesn't mean put the black meter lead to ground and pin wires with the red.


mat5153
New User

Aug 8, 2012, 4:14 PM

Post #3 of 7 (5208 views)
Re: 2002 Mit. Galant Low Voltage (p1500) Sign In

Can you please explain that test to me? I would really appreciate it.

It just doesnt make sense that my battery sees charge when its cool but not when its hot. I'm not sure where the problem is.... thats why i'm here lol. thanks.


nickwarner
Veteran / Moderator
nickwarner profile image

Aug 8, 2012, 6:37 PM

Post #4 of 7 (5200 views)
Re: 2002 Mit. Galant Low Voltage (p1500) Sign In

Ok, a multimeter set to DC volts is telling you the difference in voltage between the two points it is hooked up to. A voltage drop test shows you what is happening on a circuit under load. If you did a continuity test on say a battery cable that was bad it would still pass if just a few of the strands were intact because a meter tests it with a very small amount of voltage. But obviously it would do nothing when you tried to start the car. You find the wire that feeds power from the alternator to the battery. Place one lead on the battery positive and the other on the alternator stud. Run the engine with the meter set to DCv and note the reading. You will be measuring the difference between the two points, or how much voltage dropped along the way and never made it to where it was supposed to go. Think of it as your lawn sprinkler. You have the water on and if you were looking at the pressure at the spicket it would look good but if you were pinching off the hose (resistance to flow) it wouln't make things work at the sprinkler. Usual rule of thumb is .1v drop per connection. You start seeing .5v and up you know you have an issue. Do that to the field coil terminal, power cable and the ground. It works to show voltage drop on ground circuits too. Its results are only valid when the component is energized. If you wanted to VD test a starter cable the only reading that would mean anything was when you were cranking it over. Get a baseline reading when its working right and bring your meter with as you drive. When it acts up, hook up to it and do the tests again. Maybe a bad wire is getting high resistance when heated. You will know which one it is when you have the results from the VD test. When talking about this test in front of your wife make sure you call it by its full name or she will think you are the one getting the test and will wonder why in a less than happy way.


mat5153
New User

Aug 9, 2012, 4:09 PM

Post #5 of 7 (5187 views)
Re: 2002 Mit. Galant Low Voltage (p1500) Sign In

I have to get myself a multimeter I guess.

Hey, I did notice something today with car. The oil pressure light comes on when the voltage drops.

When I was driving (the alternator was charging) I turned on the headlights and AC this resulted in the voltage taking a sudden drop and the oil pressure light coming on. It only shut off when I hit the gas hard and the voltage recovered.

Typically, the oil pressure light comes on whenever the alternator isn’t charging and I come to a stop at a red light. I'm not sure if any of this information is meaningful, just throwing it out there.

Thanks,


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 9, 2012, 4:30 PM

Post #6 of 7 (5183 views)
Re: 2002 Mit. Galant Low Voltage (p1500) Sign In

Are you sure it's just not idling too low causing all of that?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



mat5153
New User

Aug 10, 2012, 5:30 AM

Post #7 of 7 (5169 views)
Re: 2002 Mit. Galant Low Voltage (p1500) Sign In

Hey Hammer,

The alternator doesn't charge the battery while driving if the car has been sitting in a sunny parking lot above 90 degrees.

I don't think the idle is the concern.

Thanks for the thought though...






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