Battery light on
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Battery light on
My buddy is having an issue with his truck. Its a 99 with the 4.6L. His battery light came on last night. It was dead this morning so I had to jump him. I hooked my OBDII reader up and it said it was putting out 14.3 vlts. Got to the auto store and they checked the alternator. The guy said the alternator was good. He checked the battery and said it was bad. We got the battery replaced for free since it was still under warranty so it didn't cost anything. On the drive back my buddy said his light came back on. He said the battery gauge slowly started going down. Whats your guys thoughts? I think its alternator but I do not want to tear into it and that not be the issue. The battery terminals all look good. What sucks is I'm at college so I don't have my big tool box like I do at home.
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From: Hernando Ms
Just because the Alternator is putting out 14.3 volts,doesent mean its ALL DC,If I have my guess,one or more of the rectifier diodes in the alternator are bad.This would explain the "dead" batt,and also the fact that the dreaded light is back on.
Alternators initially generate AC,then the diode bridge changes it to DC.This bridge also acts as an electrical "dam" preventing battery voltage from backing up into the alternator while the engine is not running.
Hope this helps.
Alternators initially generate AC,then the diode bridge changes it to DC.This bridge also acts as an electrical "dam" preventing battery voltage from backing up into the alternator while the engine is not running.
Hope this helps.
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From: Hernando Ms
From what I remember,a mere load test is hooked up directly across the Battery terminals,and pretty much includes a Variable resistor(LARGE) and current meter.This procedure will not advise of any AC being introduced(as in bad diode).
I think that most reputable A/P stores should have a machine that will actually run the alternator,check the output,and confirm/deny the existance of A.C. voltage in the output.
It will have to be removed for that procedure.
I have seen alternator testing devices that are connected in series with the Battery...these should show any abnormalities,and the alternator stays in place.
I think that most reputable A/P stores should have a machine that will actually run the alternator,check the output,and confirm/deny the existance of A.C. voltage in the output.
It will have to be removed for that procedure.
I have seen alternator testing devices that are connected in series with the Battery...these should show any abnormalities,and the alternator stays in place.
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I have no problem removing it. I've worked on plenty of vehicles and work on tractors on the farm. I thought they did have machines but I guess I will call first to make sure.
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From: Hernando Ms
FYI....Charging a Battery with any AC voltage can kill it relatively quickly.If the new battery hasnt been subjected to this situation for too long it should recover after being properly charged.
May be way wrong here,but if I have my guess,youll find the battery ok,but partially discharged,and most likely at least 2 diodes in the rectifier bridge either open/shorted.
I have doubts that the A/P place will be able to tell you anything other than you have bad diodes.the bridge will have to be removed,and each diode "metered" to find the bad ones.
The more diodes shorted,the more percent of AC is put out.
May be way wrong here,but if I have my guess,youll find the battery ok,but partially discharged,and most likely at least 2 diodes in the rectifier bridge either open/shorted.
I have doubts that the A/P place will be able to tell you anything other than you have bad diodes.the bridge will have to be removed,and each diode "metered" to find the bad ones.
The more diodes shorted,the more percent of AC is put out.
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Alternator Light on- Probably bad
My guess guys, it's a bad alternator ? My 97 4.6L has 210,000 and is on it's 5th alternator. My last one the light came on because I bumped the terminal in the back while changing plugs out. I took it off and to the aP store and found out it was fine, but they replaced it because the bearing was starting to go. I purchased the lifetime warranty on the first one, best thing I ever did. Good luck with that, and please post results.
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From: Hernando Ms
FYI...stay AWAY from Autozone Remans...bad news.
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