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Old 06-30-2015, 08:11 PM
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2000 grand cherokee 4.0 charging

I have a 2000 with 4.0 the volt guage reads just above 9 volts but when checked at battery it reads 16 volts. And engine runs rough. Unplug the alternator and it runs good. Need help have no idea thinking it is the pcm.

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  #2  
Old 06-30-2015, 10:39 PM
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Re: 2000 grand cherokee 4.0 charging

Welcome to the garage.
The voltage indication on the instrument panel comes from the PCM and also the voltage regulator is inside the PCM. I would first make sure that all electrical connections are good and clean, ie check the battery clamps and also check the connectors on the PCM. Disconnect the negative battery clamp before taking the PCM connectors off. Check for moisture and/or corrosion on the pins.
How is the battery voltage, measured on the battery, with the engine off and what does it indicate on the instrument panel?
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Old 07-01-2015, 06:10 AM
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Re: 2000 grand cherokee 4.0 charging

I have checked all connectors they seem fine and clean have cleaned all connectors on pcm and when not running at the battery i have 12.5 volts and guage is the same as when running just over 9 volts and i tested the guage by pushing the odometer reset and turned on the key and it goes all the way to right and back down like it should.
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Old 07-01-2015, 08:00 AM
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Re: 2000 grand cherokee 4.0 charging

Then indeed the PCM seems to be the culprit. For whatever reason its seeing 9V coming from the alternator and it most probably puts the alternator field at max. Donīt continue driving like this, because it will harm the battery and can also damage other electronic equipment.
Not completely sure where the PCM gets the actual battery voltage from, but it seems to be pin 22 from connector C1 on the PCM or pin 12 from connector C3 on the PCM. I would measure the voltage on both pins from the connectors C1 and C3, to be sure that this voltage is the same as the battery voltage. If it is, then i would suspect the PCM at faulty.
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Old 07-03-2015, 01:12 PM
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Re: 2000 grand cherokee 4.0 charging

Have a look at the next thread from an other member who has the same problem as you: 2004 Jeep Grand Cherokee Possible ECM problem
Have a look at the small connector on the alternator and use some contact cleaner on the pins and see if that makes any change.
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