Is my alternator dead?

Tiny
JPLAYTON
  • MEMBER
  • 1998 CHRYSLER TOWN AND COUNTRY
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 215,000 MILES
The battery light on the dash has come on sporadically for a couple of days; most recently while it was on, the radio cut out completely even the clock display was gone. Then the power door locks activated and deactivated randomly, the gauges went wild, the stopped working, then the engine cut out and won't start again. I'm thinking it's the alternator, but someone told me it's probably the computer, and someone else told me it sounds like it's just the wiring harness. Help?
Sunday, March 6th, 2011 AT 7:31 PM

4 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
Use an inexpensive digital voltmeter to measure battery voltage while the battery light is on. It must be between 13.75 and 14.75 volts. If it is low, suspect worn brushes inside the alternator. They will cause an intermittent problem for a long time before they fail completely. The brush assembly can often be replaced without removing the alternator from the engine but most people just replace the entire alternator.
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Sunday, March 6th, 2011 AT 7:48 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Could be a problem with the computer control circuit of the alternator's field generation
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Sunday, March 6th, 2011 AT 9:03 PM
Tiny
JPLAYTON
  • MEMBER
  • 2 POSTS
Thanks, caradiodoc, I should have thought of that myself. The voltage measured 11.2
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Monday, March 7th, 2011 AT 2:36 AM
Tiny
CARADIODOC
  • MECHANIC
  • 34,330 POSTS
Next measure the voltage on the two small terminals on the back of the alternator, again, while the engine is running. They might be two wires that are plugged in or they could be two small nuts under a black plastic block that the wires go into. One will have full battery voltage. The other one is the key. It is supposed to be less than battery voltage but not 0 volts. If you find 0 volts, the brushes are open. If you find the same voltage on both terminals, either the voltage regulator circuit inside the Engine Computer is defective, (pretty rare), or the wire going to it is broken. If you find around 4 - 11 volts, that part of the system is working. There could be a defective diode in the alternator but I don't think that will turn the warning light on.
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Monday, March 7th, 2011 AT 2:51 AM

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