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Randall C
Randall C, ASE Master Tech
Category: Cadillac
Satisfied Customers: 12719
Experience:  ASE Master Tech, 32 years exp,Cadillac 6 yrs
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Cadillac Deville 2003 DEVILle have a service charging system

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2003 DEVILle have a service charging system message on display have a battery not charging message and the battery idiot light is on. battery tests good. removed alternator (not easy) and had it tested as well. tested good. with the battery at full bench charge 12.6v. when installed in vehicle it show no additional voltage from the alternator when running (should be up around 14v) with engine off there is 12v at the pos contact on the alternator indicating continuity between the battery and alternator. is there a charging system relay module somewhere, what else could it be?
Hello, My name I Randall. I will do my best to assist you with your question.

Sorry for the delay/ust logged in to see your question

Actually the charging system is a bit more complex on your car than the older conventional charging systems. The charging is controlled by the cars PCM ( computer)

Since battery and alternator have been tested ok, the dash reads what is is upposed to, i can only lean to a fialed charge control circuit within the PCM. It is not signalling the regulator to turn on.

To accurate diagnsoe requires a scanner hooked up to view data from the PCM. Without this, I can only lean to PCM problem

You have confirmed 12 volts on large lead to alternator from battery, you then need to check for 12 volts with key off at the orange wire at alternator. If you have 12 volts there as well. this leads evn more to PCM problem.

here is the formal description of the system per the repair manual expalining how it works

When the engine is running, the generator turn-on signal is sent to the generator from the PCM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator.
When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator F terminal is connected internally to the voltage regulator and externally to the PCM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the PCM that a problem exists. The PCM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives battery positive voltage that is Hot At All Times through the DIM fuse in the rear fuse block. This voltage is used by the regulator as the reference for system voltage control.
Customer: replied 5 years ago.

would there be a trouble code that my obd reader will pick up that indicates any of this/

it is possible. 50/50 on that but.. the code reader would have to be able to read all types of codes B,C as well a P codes. B codes are body codes which a charge problem could? set. many readers outside of shop scanner cant read body codes
Customer: replied 5 years ago.

let me check this.....will be back in a few min

Customer: replied 5 years ago.
ok code my code reader is worthless, is there anything between the alternator and battery other than the pcm such as a relay or fuse that could be causing this, pcm's are not cheap and I want to eliminate all other possible causes before I have to go that route
here is the diagram. You will see the big red wire direct from battery you confirmed 12 volts on. I then said you need to check the orange wire for 12 volts with key off. if both have 12 volts,you will then see the remaining 2 wires go to PCM, then to cluster. Nothing else in between

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