Alternator failed diode test?
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Alternator failed diode test?
Stopped by O'RiellyAuto Parts after work last night. I was admiring the reflection of my retrofitted headlights and switchback bumper lights when I noticed an ad on the window stating "free battery tests". After passing the battery test, the associate offered to check my alternator. The test device he used indicated that I failed the "diode test". Is this some marketing trickery or should I go ahead and replace my alternator? If yes, what would be the best alternator for a '94 F-150 (302 V8 5.0)?
Logistics Pro
Joined: Mar 2005
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From: Mexico, Missouri
I know of the device as that was used 11+ years ago on my '92, 300, when the truck died in the O'Reilly parking lot and nobody next to me would even bother to help me, but a young guy I knew.
After checking several things, he brought the device out and tested it and it showed the diodes had failed/shorted out, causing the alternator to fail. Upon finally getting the truck started when the battery and alternator had cooled off, I promptly got home, removed the alternator and had it checked at Carquest and O'Reillys and it failed at both places. O'Reillys had the better deal on the price of the alternator and since the young guy was there, I just swapped it with him since he knew me.
Just my experience..
After checking several things, he brought the device out and tested it and it showed the diodes had failed/shorted out, causing the alternator to fail. Upon finally getting the truck started when the battery and alternator had cooled off, I promptly got home, removed the alternator and had it checked at Carquest and O'Reillys and it failed at both places. O'Reillys had the better deal on the price of the alternator and since the young guy was there, I just swapped it with him since he knew me.
Just my experience..
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
It's not a marketing gimmick, or at least it shouldn't be. You could try getting another opinion, (test it again).
There are six diodes, three positive and three negative, in your alternator that convert alternating current to DC. If it turns out you have a diode/bad alternator, and it sounds like that's the case, you want to be sure to remedy the underlying cause of this since it involves the heart of the electrical system. If it's the OEM alternator you may want to consider replacing the diode pack and rebuild it yourself.
Don't want to have to keep replacing alternators.. Or batteries.. or golly knows what el$e. Check voltage drop at ground and positive connections for example.
http://www.aa1car.com/library/charging_checks.htm
There are six diodes, three positive and three negative, in your alternator that convert alternating current to DC. If it turns out you have a diode/bad alternator, and it sounds like that's the case, you want to be sure to remedy the underlying cause of this since it involves the heart of the electrical system. If it's the OEM alternator you may want to consider replacing the diode pack and rebuild it yourself.
Don't want to have to keep replacing alternators.. Or batteries.. or golly knows what el$e. Check voltage drop at ground and positive connections for example.
http://www.aa1car.com/library/charging_checks.htm
Elder User
Joined: Jul 2011
Posts: 793
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From: Vernon, BC
It's not a marketing gimmick, or at least it shouldn't be. You could try getting another opinion, (test it again).
There are six diodes, three positive and three negative, in your alternator that convert alternating current to DC. If it turns out you have a diode/bad alternator, and it sounds like that's the case, you want to be sure to remedy the underlying cause of this since it involves the heart of the electrical system. If it's the OEM alternator you may want to consider replacing the diode pack and rebuild it yourself.
Don't want to have to keep replacing alternators.. Or batteries.. or golly knows what el$e. Check voltage drop at ground and positive connections for example.
Alternator & Charging System Checks (Alternator Testing)
There are six diodes, three positive and three negative, in your alternator that convert alternating current to DC. If it turns out you have a diode/bad alternator, and it sounds like that's the case, you want to be sure to remedy the underlying cause of this since it involves the heart of the electrical system. If it's the OEM alternator you may want to consider replacing the diode pack and rebuild it yourself.
Don't want to have to keep replacing alternators.. Or batteries.. or golly knows what el$e. Check voltage drop at ground and positive connections for example.
Alternator & Charging System Checks (Alternator Testing)
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