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2009 CTS Luxury
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30 Posts
Discussion Starter #1
99 DeVille. Has been running good. Battery volts always has been at 13.4V while driving. No starting issues. Driving home last night volts drop to 12.9 lights a little dim. Down to 12.7 by the time I get home. Battery at 12.6 after engine stopped key on.
Next morning starts right up volt go to 13.4V after driving 3 miles volts drop to 13.2- 13.1- 12.9 stays there. No load change.
Not sure if alternator or maybe a battery going bad? I know you all say volts should be 14.4 0r so when charging, but mine has never gone above 13.4 since I got car. Any suggestions? Thanks.
 

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Alexandra - 96 SDV Clyde - 15 Silvy
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6,394 Posts
You can get the battery tested for free at most parts stores. I think they test alternators too, so diagnostics should be easy.

From a parking lot wrencher perspective, I would say yeah, sounds like it's not putting out enough juice. Get 'em tested and report back.
 

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2009 CTS Luxury
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Discussion Starter #3
So battery tested ok. Replaced alternator. First started went to 14.2V then settled in at 13.8v. Seems to go between 13.6v and 14.2v. Maybe need to replace tentioner/pulley???
PS: Alternator came out bottom real slick.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,441 Posts
Your engine running DIC voltage should show between 14.2 and 14.8 volts - all the time - depending on rpm and electrical loads.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,268 Posts
So battery tested ok. Replaced alternator. First started went to 14.2V then settled in at 13.8v. Seems to go between 13.6v and 14.2v. Maybe need to replace tentioner/pulley???
PS: Alternator came out bottom real slick.
==========================
Replaced alternator.
I hope you didn't buy an auto parts store "house-brand" rebuilt -
 

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1992 DeVille
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2,339 Posts
So if im reading this right, if the obd display reads 13.4 that's too low? Hmm that's about what mine reads engine running at idle
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,268 Posts
So if im reading this right, if the obd display reads 13.4 that's too low? Hmm that's about what mine reads engine running at idle
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your car is completely different than the OP's 99 Deville -
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,268 Posts
Yeah I know. Just thought someone who knows could weigh in. If not, no big deal.
============================
for YOUR car - 13.4 is normal -

for a newer Northstar powered car - 14.2 to 15.1 is normal -
 

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2009 CTS Luxury
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30 Posts
Discussion Starter #11
So this morning go out and start car and it goes right to 14.4v. Going on a trip today so will see how it performs. It was a Delco rebuilt unit.
 

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2009 CTS Luxury
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Discussion Starter #12
So Take a 200 mile trip yesterday. Car runs great! Alternator starts at 14.4V. By the time we reach destination, 96 miles, it has dropped to 13.6 V.
On way home 6 hours later, it starts at 14.4V and drops to 13.6V lights and radio and auto temp on. Never goes below 13.6V lights stay bright, no issues. So this morning turn key to on, and battery reads 12.6V after sitting all night. Car starts right up and reads 14.4V at idle. Any thoughts or is the normal for my car??
 

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'98 STS (RIP @ 206,xxx miles)
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....Car starts right up and reads 14.4V at idle.
Immediately following engine crank, voltage will be at the upper end of the range while the alternator restores the battery energy that was consumed cranking the engine.
Any thoughts or is the normal for my car??
Your electrical system could be the poster child example for "normal".

There are many variables when dealing with battery based electrical systems. A small sample includes things like temperature, engine crank time, battery age/condition, quality of components in alternator voltage regulator. The list goes on and on.

Do not buy into the misleading internet "wisdom" that says system voltage should read exactly xx.yy . No two alternators are exactly the same. That's why there is a range of acceptable voltage values. There are many variables involved.
 

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1996 sedan deville
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188 Posts
So Take a 200 mile trip yesterday. Car runs great! Alternator starts at 14.4V. By the time we reach destination, 96 miles, it has dropped to 13.6 V.
On way home 6 hours later, it starts at 14.4V and drops to 13.6V lights and radio and auto temp on. Never goes below 13.6V lights stay bright, no issues. So this morning turn key to on, and battery reads 12.6V after sitting all night. Car starts right up and reads 14.4V at idle. Any thoughts or is the normal for my car??
That is how my car reacts...no problems
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,268 Posts
So Take a 200 mile trip yesterday. Car runs great! Alternator starts at 14.4V. By the time we reach destination, 96 miles, it has dropped to 13.6 V.
On way home 6 hours later, it starts at 14.4V and drops to 13.6V lights and radio and auto temp on. Never goes below 13.6V lights stay bright, no issues. So this morning turn key to on, and battery reads 12.6V after sitting all night. Car starts right up and reads 14.4V at idle. Any thoughts or is the normal for my car??
======================
Any thoughts or is the normal for my car??
that all appears to be normal -
 

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For fun, check the voltage at the battery with a digital multimeter. My 99 always reads about .5 - 1 volt lower at the DIC than what I read at the battery.
 
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