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2001 ESC
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18 Posts
Discussion Starter #1
While driving, the alt. charges anywhere from 12.6 to 13.6 V's. While in gear, at an idle with auto headlamps engaged the alt. drops to 12.1V's. Disengage auto headlamps and it goes back to 12.6V's. I have replace the alt. and the battery simultaneously. The EXACT issue remains. The alternator should actually increase in output as the load increases (yes?) and output shouldn't drop below 13.2 or so (correct?). Ideas? Thanks in advance
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,241 Posts
Welcome to CF !!! Which make, model, year, engine option? Please post the correct info and we'll move this to the correct vehicle forum. Thanks.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,241 Posts
Your charging system voltage in the DIC should show - during normal engine operation - 14.1 to 14.8 volts. We can't see amperage output, but that also varies constantly as a function of battery charge state and system loads.

Check all the battery and alternator cable connections and terminals as well as possibly install a separate alternator-to-ground strap.

Did you install a NEW Remy or AC Delco alternator? Chain store reman alternators are infamous for having screwy voltage regulators.

My STS starts up and ramps up to 14.6 - 14.9 volts for a while, then on down the highway it drops to about 14.3 - 14.4 and stays there for the rest of that drive cycle. After an overnight rest the DIC shows 12.6 volts (12 volt battery full charge). That sequence is normal for a pre-2006/2007 vehicle - the later ones have very sophisticated "smart" battery management and the old relatively fixed charging specs are out the window.
 

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2001 ESC
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18 Posts
Discussion Starter #6
Will pull DTC's on the way to church. I don't know why I haven't already done this!
 

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2001 ESC
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18 Posts
Discussion Starter #7
I like the secondary alt ground strap idea. It is a Delphi alt. I was a service manager for a Cadillac repair shop for 15 years prior to retiring 10 years ago and used Delphi alts. exclusively and rarely had any issues, but it's possible to have a bad regulator. It's just that the EXACT issue with the EXACT same numbers was encountered with the previous alt..
 

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2001 ESC
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18 Posts
Discussion Starter #8
History P 0622 is there and the infamous P 0741 (been there for three years) that I'm not concerned about. At an idle in gear it dropped to 11.8 with headlamps on 12.5 when headlamps off.
 

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Master of the Dark Art of Diagnostics
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18,709 Posts
WAIT -
I seem to remember something from several years ago -
same car - same problem - they replaced several alternators -
ALL of the alternators bench-tested GOOD -
ALL had low power output in the car -

the Eldo charging system was a little weird -
not just that the PCM controlled charging -
but there was a thermistor (temp sensor) somewhere near the battery -
that would also control the charging system to prevent the battery from overheating -
 

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2001 ESC
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18 Posts
Discussion Starter #10
I found the post your referencing and it says that thermistor is only on 98 -99 Sevilles with the battery under the back seat.
 

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2001 ESC
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18 Posts
Discussion Starter #11
I don't know if this is part of this issue (idon't think it is) I have SCREAMING belt issue. I've replaced the Tensioner assembly, idler pulley, belt (GM parts to this point), alternator(Delphi), and the harmonic balancer (wobbling). after car has run for 15 min. or so the screaming stops until you hit 1750rpm.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,241 Posts
That loose belt is most likely your problem - that alternator takes up to 11 horsepower to turn when it's jamming amps into a large electrical load - like a low battery and headlights on.

Have a good Mom & Pop shop go over the serpentine belt system, its tensioner and idler, and the belt itself. You have either the wrong belt or the wrong alternator pulley diameter, causing belt slip - a BIG no-no.

While you're at it, check the water pump drive belt system at the rear (driver's) end of the engine, too. If that tensioner pulley fails (common) you're in very expensive repair territory.

Belt routing and pulleys.gif water pump drive pulleys.gif
 

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2001 ESC
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18 Posts
Discussion Starter #13
Everything mentioned was installed by a highly qualified and certified ASE World Class Master Tech
 

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2001 ESC
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18 Posts
Discussion Starter #14
...and the water pump abd belt were replaced recently at Tom Peacock Cadillac. As stated in my previous post the Idler pulley, tensioner assembly and belt are genuine GM parts.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,241 Posts
Whatever you say.

Most of us place little or no faith in quoted "Master Techs". They've been proven wrong too many times in these forums. So have quite a few Cadillac dealerships.

Did he know that these cars have two different alternator pulley diameters? Get the wrong one and you get excessive belt slip - squeal. There are also a couple of different serpentine main accessory drive belt lengths available.
 

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2001 ESC
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18 Posts
Discussion Starter #16
I sure hope so. He worked for Peacock and David Taylor Cadillac for 20 years before buying his own shop a couple years ago but I'll ask him!
 

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2001 ESC
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18 Posts
Discussion Starter #17
Wouldn't the mark on the Tensioner assembly be outside the lines if the the pulley was wrong?
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,241 Posts
Most likely. There's an arrow or tab that traverses a marker casting as the belt wears.

Typical belt gauge

Belt tensioner gauge.gif
 

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2001 ESC
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18 Posts
Discussion Starter #19
WAIT -
I seem to remember something from several years ago -
same car - same problem - they replaced several alternators -
ALL of the alternators bench-tested GOOD -
ALL had low power output in the car -

the Eldo charging system was a little weird -
not just that the PCM controlled charging -
but there was a thermistor (temp sensor) somewhere near the battery -
that would also control the charging system to prevent the battery from overheating -
Most likely. There's an arrow or tab that traverses a marker casting as the belt wears.

Typical belt gauge

View attachment 571312
Then it has the correct pulley. I've had this car to three reputable (a large mom and pop, a Cadillac dealership, and the aforementioned Cadillac specialty shop) over the last two years for this one. The alt. thing just started a few weeks ago.
 

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Super Moderator
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86,068 Posts
Have you double checked the battery? I know you said it was replaced, but I've had a bad battery twice, right off the shelf. Not common, but not unheard of.
 
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