Battery Light on @ Idle
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Battery Light on @ Idle
Batteries were dying. I was trying to wait til payday but the wife said while I was on the road the battery light kept coming on. Charged two new batts today, still have the batt light on when below about 1100 rpm. 2005 6.0 PS.
Note: tried to search for this but kept getting hundreds of hits- no time to wade thru it all. Sorry.
Note: tried to search for this but kept getting hundreds of hits- no time to wade thru it all. Sorry.
Cargo Master
Joined: Feb 2008
Posts: 2,862
Likes: 44
From: Tooele, UT
a lot of people have the misconception that when the battery light comes on it's the battery. if the light comes on while the vehicle is running period it's the alternator. the only thing the batteries are used for is starting the truck. after they are recharged they don't do anything until the alternator takes a dump then the power is drawn from the batteries.
Hotshot
Joined: Jul 2005
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From: Middle Tn.
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So, great sages and emminent techies, any threads around for checking the alternator with my trusty Radio Shack-O-Meter? Tried to locate a service manual in pdf form but no joy, although it did return 247 pages of hits, no matter how I filtered my search. Oops, off-topic, sorry again. Old Guy...
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Check your battery voltage with the engine off. Make sure its around 12V Make sure all your connections are tight and clean. Then check your voltage while cranking the engine.
Scenario #1
If voltage drop to 9 or 8 volts while cranking you either got some discharged batteries or weak batteries that are going south.
You need to either recharge your batteries or have them load tested to make sure they are good. Voltage may not drop that much while cranking the engine.
Also disconnect the batteries and check your voltage with them disconnected. The voltage on each one of them should be the same. If you have one battery with 12 or 11 volts and the other one with 8 or 10 volts that's the bad one. If you want to replace just one or both is up to you.
Scenario #2
If you check your battery voltage while cranking and the voltage don't go that much down, then it should raise all the way up to around 13.8V with the engine running. If the voltage don't raise up to 13.8V, with the engine running, and you are sure that your batteries are 100% good then you may have alternator problems.
Good Luck...
Scenario #1
If voltage drop to 9 or 8 volts while cranking you either got some discharged batteries or weak batteries that are going south.
You need to either recharge your batteries or have them load tested to make sure they are good. Voltage may not drop that much while cranking the engine.
Also disconnect the batteries and check your voltage with them disconnected. The voltage on each one of them should be the same. If you have one battery with 12 or 11 volts and the other one with 8 or 10 volts that's the bad one. If you want to replace just one or both is up to you.
Scenario #2
If you check your battery voltage while cranking and the voltage don't go that much down, then it should raise all the way up to around 13.8V with the engine running. If the voltage don't raise up to 13.8V, with the engine running, and you are sure that your batteries are 100% good then you may have alternator problems.
Good Luck...
Postmaster
Joined: Mar 2007
Posts: 2,612
Likes: 2
From: Dunwoody, GA
If you don't have close to 14v after 30seconds of the engine running your alternator is bad. Just take your truck to any chain auto parts store and they will most likely have a battery charger/tester and an alternator tester that they can use for free.
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Seems to have been transient. As I said, I changed both batteries on Thursday 5/7 because they were getting weaker and weaker. On 5/4 my wife had to run me to New Orleans to catch a flight and on her way back to Ole Miss she noticed the batt light came on when idling. I got home 5/6 and got new batts next day. Didn't get the light again until leaving a doctor's appt with about 15 miles on the new batts. Again it only came on at idle.
Just went out with my Shack-O-Meter and I've got 14 volts at idle, 13.7 with the lights on. I checked at both batts and at the alternator post-to-ground. Seems okay now, but I'm gonna keep a suspicious eye on it. 100,700 miles on this 2005.
Just went out with my Shack-O-Meter and I've got 14 volts at idle, 13.7 with the lights on. I checked at both batts and at the alternator post-to-ground. Seems okay now, but I'm gonna keep a suspicious eye on it. 100,700 miles on this 2005.
