over charging problems

I have a 99 dodge with a Cummins. During a winter snow storm, the truck experienced an unusual problem. The charging rate (on the amp meter) jumped
to about 16 volts. This caused the head lights to brighten and the air bag light and chime went off. This problem would cycle on and off inconsistently. Once the air temperature was back to normal the trouble disappeared. The dealer could find nothing except that there was a record of an overcharging. I thought it was related to cold and wet conditions until late Friday when it happened again. However, there was nothing related to cold and wet. The problem is definitely inconsistent. This morning on the short drive to the dealer, the amp meter jumped to over charge position twice and the air bag light and chime went off. The moment I arrived at the dealers lot, the charging rate returned to normal. They have never had such a problem. My guess is it is related to whatever controls the charging. I replaced the batteries after the first trouble, however, obviously that was not the problem. Has anyone had such a problem. Any suggestion on what module that I should consider replacing? Anyone have any idea how the charging system works as there is not voltage regulator. Is there a relay somewhere. The dealer seems at a loss. any thoughts would be appreciated.
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There is, but it's built into the PCM. The only other external sensor that the PCM uses to regulate voltage is the battery temp. sensor, which is located underneath the battery (not sure which side on a Cummins-powered truck - most likely the driver's side battery).
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Initially, it seemed related to temperature, as there was snow and rain. Also, wondered if it could be related to the manifold heaters. I will see if I can see anything related to the battery sensor. Batteries and sensors sounds like corrosion. Dealers never suggested any solution except come back when it is occurring.

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manifold pre-heater cycling on and off ?

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Tom Lawrence wrote:

Yes, the temp sensor is on the bottom of the battery tray under the driver's side battery. The passenger side tray doesn't have one.
--
Ken



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I will check that sensor out thanks. Anyone know how much the PCM costs? Where is it located exactly?

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Passenger-side firewall. Three big rectangular connectors going to it. Dealer has it for around $600... EBay should be around half that. Be careful looking around... you want the Dodge "P"CM, not the Cummins "E"CM that mounts on the driver's side of the engine. It's the Powertrain Control Module that handles the alternator output, the ECM just runs the engine.
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