Battery charge voltage too high on 06 XK - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 4 (permalink) Old 12-05-2014, 11:36 AM Thread Starter
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Exclamation Battery charge voltage too high on 06 XK

Hi Guys, My 06 Commander shows 16.5V when charging the battery @ idle. I just replaced the battery & the alternator tested good @ the local part store. Cables & wiring look clean & solid. I'm thinking it's a bad reguator which is on the PCM.
Has anyone had similar problems, replaced just the regulator or does the whole PCM have to go?
Thanks in advance for the help!
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post #2 of 4 (permalink) Old 12-18-2014, 05:31 AM Thread Starter
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Hello all, After a little more time has passed I beleive it is the alternator going bad. I connected my DVM to the 12V accessory plug and watched it while driving to and from work. At times the voltage would go as high as16.5 to 17V!
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post #3 of 4 (permalink) Old 01-08-2015, 01:03 PM
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AFAIK 99% of the time an alternator "goes bad" when the bearings fail and the rotor vibrates on the shaft and wears out the brushes.

You are guessing the voltage regulator is defective and the field is driven full power and overcharging the battery which will soon boil-out.

IIRC Chrysler vehicles don't have a voltage regulator in the alternator. The microprocessor that does the engine and emissions control samples the power bus voltage and sets the alternator field current. It should have set the MIL (check engine light) if the charging system malfunctioned - as far as it could tell. You don't need a DRB3 to figure out what it thinks the bus voltage is, even fairly simple scan tools can get that much from it. If it reads 14.4v and you read 16.5v on the battery, then either there is 2.1v of voltage drop on the power lead to the controller, or the ground at the controller is 2.1v higher than the ground at the battery, or a combination of both that adds up to 2.1v. Its also possible the control module is defective, but given the vehicle's age, a corroded connection is more likely and less costly anyway.
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post #4 of 4 (permalink) Old 01-08-2015, 01:25 PM
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Like Poly said, the Charging System Warning Light (the little battery on the dash) should go off if the electric systems voltage is too low or too high or the PCM senses a fault in the field control of the alternator.

First, are you're sure the tools you're using to measure the voltage is accurate? Have you tried another tool to confirm they're both reading the same voltage and one might NOT be off?

If the voltage is truly that high, and its NOT lighting a Warning Light on the Dash, then its most likely because the PCM doesn't see the voltage being as high as it is. And since the PCM is controlling the voltage, I suspect that is your problem right there. NOT a bad alternator or a bad PCM.

Like suggested, corrosion on the connectors for the field control or voltage sampling might be at fault. Bad or corroded grounds might be at fault. They create resistance, which will create a voltage drop or in the case of grounds, a mis-reference for the voltage, the PCM might think its at 14.5VDC when in reality it is holding 16.5VDC.

First confirm your measuring tool is accurate, try another one.
Then I'd try cleaning the connectors with spray electrical cleaner, use a wire brush to remove any built up dirt or corrosion, treat with dielectric grease and reconnect. The would be the control connectors to the alternator and the connectors to the PCM.
Then start checking grounds, disconnect them and clean them and reconnect.


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