Rick's Free Auto Repair Advice

Alternator overcharges battery Impala

How to fix an Alternator that overcharges battery Impala

Shops are reporting instances where GM vehicles and specifically Chevrolet Impala alternators are overcharging the battery. The charging system in these newer GM vehicles is far more complicated than just a traditional voltage regulator and alternator. These systems incorporated and Electric Power Management (EPM) strategy to reduce the amount of time the alternator runs when charging isn’t needed. That saves gas. The system also monitors the state of battery charge when the engine is turned off. The body control module (BCM), engine control module (ECM) communicate charging and battery condition and use inputs from a battery current sensor. Corrosion anywhere in this system can produce high voltage drops that can really mess up the instructions to the alternator. So always start by conducting voltage drop tests.

1. Set your digital multimeter to the millivolts scale.
2. Start engine and touch one meter lead to the battery negative terminal and the other to the alternator case. The reading should be less than 50-mv. If it’s more than that, clean the battery ground cable.

3. Next, touch one meter lead to the battery positive terminal and the other to the battery output terminal stud at the alternator. The reading should be less than 300-mv. If it’s more, check the condition of the connection, clean corrosion and re-test.

4. With the engine off, disconnect the “Field” connector at the alternator. Then start the engine and check the battery voltage at the battery. It should read 13.8-volts. If the voltage drops check out from the previous steps and the voltage isn’t 13.8 volts, the alternator is bad. Replace it.


© 2012 Rick Muscoplat

Posted on by Rick Muscoplat

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