2003 Seville SLS Charging issue

[Cadoo2]

Hello gentlemen.. Picked up my very clean  03 SLS for a song as a play/project car. 130k miles, loaded, Galaxy silver w/cloth top and gray interior. Everything works except the rear air ride but my immediate  issue is voltage. I have an intermittent alternator/charging issue. Battery checks out, terminals clean, no "dimming" of accessories. 

One day she shows 14.3-14.5 volts on the display and on multimeter and run fine , next day it'll run down below 11volts and eventually kill the battery. Driving/idling no difference. It'll take a charge and might be fine for 10 start/stop cycles or it'll drop out again. it's a crap shoot. I know the "service charging system" display isn't a ghost because the battery will die. 

I understand that the voltage regulator is internal to the PCM.  I've never had an alternator "come and go" so I may have an intermittent ground fault?

I'm stumped.. The alternator is a 3-4 hour buried juggernaut of a swap so I'm hesitant to "just swap the alternator" before I rule out a simple fix. 

 

Any help or insight is GREATLY appreciated!!

[rockfangd]

Welcome to Caddyinfo.

If yours is like the 90s style I would suggest inspecting the plug that goes to the regulator on the alternator. I have misdiagnosed alternators on these because of that plug. Wire will corrode somewhere near the plug and intermittently lose connection

[Cadoo2]

Thanks... That's where I'm leaning. The intermittent nature of the thing has me believing it's a connection or ground issue.  Getting older has afforded me the patience to consider and ask questions vs. throwing parts at issues. I would've cleaned all the contacts while swapping the alternator and would've never known the issue was as simple as a wire brush and some Noalox 

[Logan]

Just FYI.....my 2001 had higher voltage. Like 16.1 volts at times. At the time I think those readings were considered normal vs the cars from the late '90s. 

Cars that have remote batteries (under the seat or in the trunk) have exceptional battery life. The car may only be on it's second battery. I know of a 2008 Cobalt in Michigan that still has it's original Delco battery mounted in the trunk. So it could be a goofy battery starting to fail. 

 

 

GM service manual info for the 2003.....copy and paste transfers over differently.....so a little bit scrambled.  

 

 

Step
 Action
 Value(s)
 Yes
 No
 
(1)
 Did you perform the Diagnostic System Check for Engine Electrical?
 --
 Go to Step 2 
 Go to Diagnostic System Check - Engine Electrical 
 
(2)
 Important: The battery must be above a 70 percent state of charge. 

Did you perform the Battery Inspection Test?
 --
 Go to Step 3 
 Go to Battery Inspection/Test 
 
(3)
 Install a scan tool. 
Start the engine. 
With a scan tool, command the GEN-L Terminal OFF and ON. 
Observe the Ignition 1 Signal parameter. 
Does the voltage change with each command?
 --
 Go to Step 4 
 Go to Step 8 
 
(4)
 Turn ON the following accessories: 
•  Headlights -- high beams 

•  A/C on Max 

•  Blower fan -- ON high 

•  Heated seats -- if equipped 

With a scan tool, observe the ignition 1 signal parameter in the engine data list. 
Increase engine speed to 2,500 RPM. 
Is the voltage within the specified value?
 12.0-15.5 V
 Go to Step 5 
 Go to Step 6 
 
(5)
 Turn OFF all accessories. 
Turn OFF the ignition. 
Caution: Make sure that the load is completely turned off before connecting or disconnecting a carbon pile load tester to the battery. Otherwise, sparking could ignite battery gasses which are extremely flammable and may explode violently. 

Connect a carbon pile tester to the vehicle. 
Important: When measuring generator output current, be sure the inductive probe encircles the generator output wire. 

Connect an inductive ammeter probe to the output circuit of the generator. 
Start the engine. 
With a scan tool, command the GEN-L Terminal ON. 
Increase engine speed to 2,500 RPM. 
Adjust the carbon pile as necessary in order to obtain the maximum current output. 
Is the generator output greater than or equal to the load test value as specified in Generator Usage ?
 --
 System OK 
 Go to Step 7 
 
(6)
 Is the voltage measured greater than 15.5 volts?
 --
 Go to Step 12 
 Go to Step 7 
 
(7)
 Leave the vehicle accessories ON or maintain load test value. 
Maintain engine speed at 2,500 RPM. 
Measure the voltage between the generator output terminal and the generator metal housing. 
Is the voltage measured equal to the specified value?
 B+
 Go to Step 14 
 Go to Step 9 
 
(8)
 Turn ON the ignition, with the engine OFF. 
Disconnect the generator harness connector. 
Measure the voltage between the generator turn ON signal circuit and ground. 
With a scan tool, command the GEN-L Terminal ON and OFF. 
Does the voltage measure greater than the first value ON and near the second value OFF?
 4.7 V

0 V
 Go to Step 14 
 Go to Step 11 
 
(9)
 Maintain the engine speed at 2,500 RPM and continue to operate the generator at the load test value. 
Measure the voltage drop from the battery negative terminal to the metal housing of the generator. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 
Is the voltage measured less than the specified value?
 0.5 V
 Go to Step 10 
 Go to Step 15 
 
(10)
 Maintain the engine speed at 2,500 RPM and continue to operate the generator at the load test value. 
Measure the voltage drop from the output terminal of the generator to the positive terminal on the battery. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. 
Is the voltage measured less than the specified value?
 0.5 V
 Go to Step 14 
 Go to Step 16 
 
(11)
 Test the generator turn on signal circuit for a short, or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
 --
 Go to Step 19 
 Go to Step 13 
 
(12)
 Test the generator battery voltage sense circuit, if equipped, for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
 --
 Go to Step 19 
 Go to Step 14 
 
(13)
 Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
 --
 Go to Step 19 
 Go to Step 17 
 
(14)
 Inspect for poor connections at the generator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
 --
 Go to Step 19 
 Go to Step 18 
 
(15)
 Repair the high resistance or open in the ground circuit of the generator. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
 --
 Go to Step 19 
 --
 
(16)
 Repair the high resistance or open in the generator output circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
 --
 Go to Step 19 
 --
 
(17)
 Replace the PCM. Refer to Control Module References in Body Control System.

Did you complete the replacement?
 --
 Go to Step 19 
 --
 
(18)
 Replace the generator. Refer to Generator Replacement .

Did you complete the replacement?
 --
 Go to Step 19 
 --
 
(19)
 Operate the vehicle in order to verify the repair.

Did you correct the condition?
 --
 System OK
 Go to Step 2 
 
 

[Cadoo2]

Thanks LOGAN !!  When it does charge the battery it DOES sometimes show 14.8-15.1 v and I thought that seemed high expecting the "normal" 14.3-ish voltage. 

I have a decent enough OBD2 scan tool and I may be able to perform some of the diagnostic protocols you shared. Like all electrical gremlins it'll either be a basic rubbed wire or corroded plug  OR a diabolical quest ending in madness and profanity...

It is a spare "play" car so I'm hesitant to take it in to my mechanic and pay him to chase it down...