I have only had my 02 base convertible for about a month now. I realized the other day i need to fix the vacuum to make the blend doors work on the AC, hoping to do that this weekend. I noticed yesterday on my way home with the ac blower on high the digital voltmeter was showing 13.1-13.6 and i am guessing when the electric fans would kick on the volts would drop to 12.8-13.1. I got in standstill traffic and the volts dropped down to 12.1v, i would start moving and they would go back up to 13.1. If i turn the ac blower down the volts start moving into the upper 13v range.

The car has 23000 miles on it, the battery is about 2-3 months old, and i have been driving it about 4 days a week. Is this normal or is something wrong?

 

FIRST THING....remove your battery cables and make sure they are CLEAN and then reconnect !!...The 2nd thing is DON'T use the DIC voltmeter to determine the battery state of charge !!...as you can see in the picture the voltage is picked up at the IPC which gets power from the IPC Fuse19. If you have a multimeter load the charging system with AC blower, defroster, headlights, etc and see what the voltage reading is across the battery terminals...record that figure...now like in the video go from battery positive to the stud on the alternator...record that number...I like to see .2 volts or less...On the negative side measure from the alternator case to the negative post on the battery...about same for negative side...I think when I had checked mine it was .02 to .03 volts !!...if higher check the alternator lead and the battery positive lead where they are connected down at the starter solenoid...make sure they are clean and tight . And oh BTW if it IS determined that your alternator is toast have yours rebuilt !!...other new or remans don't work on these picky cars...it will be a real Sh**show if you don't !!

 

Thanks for the information, I will check it out this weekend and post back the results.

 

@C5 Diag

i had time to mess with it this evening, this was all a based upon a cold start

At the battery 14.3 volts
At the alternator 14.38 volts
this was with nothing but the headlights on low, couldn't figure out how to turn them off

With everything on ac on high, rear defrost and high beams
At the battery 13.77 volts
at the alternator 14.15 volts

Once the cooling fans turned on plus everything else
12.36 volts at the battery
12.66 volts at the alternator

After it warms up and a few fans cycles the alternator settles at 13.1 and the battery at 12.6

DIC shows 11.5 when fans are on and 11.9 with fans off

I can rev the motor and bring the volts up but they will drop back down.

So does look like a bad alternator

 

.3 voltage drop on the positive side...not to bad...what about the ground side ??...you have to check both sides !!

 

How do I check that?

 

Just put red voltmeter lead on alternator case and negative lead
on negative battery post...whatever the voltmeter reads is the voltage drop !!
just think of the voltmeter leads as a bridge you are making..,you want the electrons flowing through the wiring...if it finds it easier to flow through the voltmeter leads it would rather do that...that’s an analogy of voltage drop !!

 

Turn off twilight sentinel and your headlights will not stay on in your garage.

 

Ok trying again

Cold start nothing on

14.39 at battery

14.45 at alternator

assuming I did it right red lead on alternator case the black on negative of battery. 26.4 but that doesn't seem right

Everything turned on ac, headlights and defrost
battery is 13.91
alternator 14.14
69volt drop from alternator case to negative

once it gets to operating temps and the fans turn on the volts drop
12.62 at alternator when fans kick on
12.33 at battery
64 volt drop


​​​​

 

From battery negative to the actual metal

case of a the alternator you should see less than .5 volts... ARE YOU MEASURING OHMS ??...A lot of us don’t understand ground to ground voltage drop testing !!!...hope this video helps !!

 

The meter is probably reading millivolts. In other words, it wasn't 26.4V but rather 26,4mV or 0.0264V that the meter was reading. Look at the meter for a mV instead of V on the display. The readings are great if that is the case.

Maybe the car has an under-drive pulley on it. That could be why the alternator doesn't keep up at idle but raises the voltage when you hold it at a higher rpm.

 

I think my meter is reading millivolts. The meter only has one option for DC and it is auto ranging. I am going to borrow one of the Fluke meters from my work to mess with it some more tonight. The video that was posted above made a lot of sense.

 

Hope the video helped...many only think... "red lead positive" and "black lead negative"...."WHAT ???...you can go from battery negative to ground ??...how does that work" ??...LOL !!...this picture depicting .02 volts is from my alternator case to battery negative and the other is .13 volts...from battery positive to the alternator stud. If you do it this way you don't have to do the subtraction...you don't have to read the voltage on battery positive to ground and then from the alternator stud to ground and then subtract...just think of the voltmeter leads as a bridge between the 2 test points you are checking...the voltmeter is saying "hey guys there is too much resistance on that circuit....no one is on my bridge....come on...come on"...that's basically what you are reading...the resistance of electron flow on that back upped bridge !!

 

Ok I redid the test with a Fluke meter from my office.

Everything off


Alternator
14.20v
Battery
14.1v


Ground drop
Red to alternator case black to battery negative
.026 volts
Battery positive to alternator stud
.127v


Everything on plus cooling fans
Alternator
12.97
Battery
12.58v
Red to alternator case black to battery negative
.078v
Battery positive to alternator stud
.379v
11.8 v on the dic




Ok so what does this tell me?

 

You need an alternator !!

 

I'd pull apart the main stud connection at the solenoid, clean the wire lugs and put it back together.