1995 Chrysler LHS Charging system failure

JOHN CONNELL

MEMBER
1995 CHRYSLER LHS
3.5L
6 CYL
FWD
AUTOMATIC
310,000 MILES

Battery light came on while my wife was driving home from work. She shut down all available power being used but still barely made it home. I put a volt meter across the battery terminals while running the engine but do not see a charge from the alternator at any RPM. If I drive it more than 15 minutes, the battery light comes on. While the battery is being depleted. The alternator was bench tested at the parts store and reported back as "passing" their tests, done twice for assurance. I don't know what else to test. I don't know what could have gone wrong while she was driving home. Any ideas? I'm not an electrician and have limited funds available as you can see from the mileage on my cars. Sure appreciate your thoughts. John

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

The last thing you want to do is remove the alternator for testing. That prevents testing of the entire system. Also, the most common failure of these alternators is worn brushes. Those always start out as an intermittent problem, so any testing has to be done while the warning light is on.

These systems are real easy to test on the engine by measuring the voltages on the two smaller terminals on the back of the alternator. That must be done with the engine running. One will have full battery voltage. The other one must have less but not 0 volts. 4 - 11 volts is typical. If you find 0 volts, the brushes are worn. They can be replaced separately, often without even removing the alternator from the engine.

If you find exactly the same voltage on both terminals, (full battery voltage), there's a break in the wire going to the voltage regulator inside the Engine Computer.