: unsteady voltage readings



orandaberg
05-06-13, 10:54 PM
Hello
Maybe someone can shed some light on this. My voltage readings never stay the same. Now when I say that I understand there will be some fluctuations. Mine as normal when starting begins st 12.8 then slowly gies up to 14 but through out my trip to Belgium the readings would go anywhere from 12.5 back to 14 then slowly drip to 13 an back to 14 an so on. My 300C keeps a steady 14.1 with very little fluctuations. On the last leg of my 12 hr drive to Belgium my voltage went down to 12.8 and stayed there till I arrived. 2 days later dead battery. Driving the car daily starts ok with the voltage readings fluctuating between 12.5 to 14 all day. I do not dare leave tge radio o while parked for fear the car will not start. As mentioned in another thread the alternator an battery have tested ok and undsr a load showing the alternator is charging. I am going ti hook my aeoforce gauge back up so I can observe my amps. I read this is another way to test if the regulator on the alternator is working correctly. Do not know if the gm has a regulator on there alternators or if its just the earky model cars that had this. Anyone shed some light on this. Something comes to mind on me is maybe my alternator belt tensioner is going out. Guess I will see that when replacing belts. Anything I should look for in particular when looking at the tensioner, apart from the obvious?

OakSRX04
05-07-13, 11:03 AM
My 2009 has the same range. Starts at 12.3, reads 14.8 to 15.2 during typical outings. I asked the dealer if 15+ was damaging my battery and the reply was basically don't worry if the Check Engine light is off. Voltage readings will not tell you about the reserve capacity available. If yours is low you'll have battery problems.

orandaberg
05-07-13, 01:33 PM
Thanks, I have gone over 14, 14.3 max, but if I understand your readings stay at that level, not like mine within an hour it can show up to 20 different readings lasting from a few minutes down to 13, then slowly up to 13.9, stay there a ehile and creep down to 12.8 and go up to 13.5 stay there and go back to 12.8 etc etc etc

conedoctor
05-07-13, 02:13 PM
The ECU or BCM (I don't know and didn't look) control voltage based on charge of the battery and other factors, so it will bounce around. If the battery is charged is there a point in dragging the engine down wasting fuel to keep the volts up?

Where will you get an amp reading from, not sure it is good data for anything.

Not saying this is the case but there is a reason why some data is hidden from the owner, people tend to hypochondriac their cars.

orandaberg
05-07-13, 02:55 PM
Ok I can live with the fluctuations then, I shall concentrate on the draw.

orandaberg
05-08-13, 08:15 AM
OK the mechanic went to pick up the car, I left the battery unhooked for nearly 3 weeks and when he connected it it started right up so I assume I can rule out a faulty battery!

While checking for battery draw, anyone know the acceptable milli ohm draw for the SRX

orandaberg
05-09-13, 03:05 AM
Bump

glake89
05-09-13, 11:19 AM
You'll be looking for milliamps. Won't be much and when you pull the offending fuse, you'll know.

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You can isolate the entire rt. or lt. rear fuse blocks at the under hood block. 50A fuses are labeled LPDB 1&2 and RPDB 1&2.

Mr.electric
05-09-13, 11:32 AM
I would guess your alternator is starting to fail but has not totally died yet. During your long trip your alternator is charging for the first few hours then gets weak and quits. It would pass any number of tests while it works, fail every test if you tested while it is not charging. If you want to be safe money wise wait until it stops charging all the time. If you want to be safe reliability wise replace it now. Of course I could be wrong and it is some unusual battery computer failure as mentioned in a previous post. I have never been aware of a battery computer in non hybrids but it makes sense. I have seen battery temp sensors on newer 12v batteries those must lead to one of the computers....

conedoctor
05-09-13, 11:33 AM
Almost like they designed it like that ;)

orandaberg
05-09-13, 11:41 AM
Under hood block?(fuse box) So pulling one of those 50A fuses will show which side is drawing current? then start pulling fuse according to side?

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I would guess your alternator is starting to fail but has not totally died yet. During your long trip your alternator is charging for the first few hours then gets weak and quits. It would pass any number of tests while it works, fail every test if you tested while it is not charging. If you want to be safe money wise wait until it stops charging all the time. If you want to be safe reliability wise replace it now. Of course I could be wrong and it is some unusual battery computer failure as mentioned in a previous post. I have never been aware of a battery computer in non hybrids but it makes sense. I have seen battery temp sensors on newer 12v batteries those must lead to one of the computers....

Technically I should be getting a light on the panel, if it fails anytime during operation? There is a DIC indication check charging system if it fails

Mr.electric
05-09-13, 12:42 PM
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Technically I should be getting a light on the panel, if it fails anytime during operation? There is a DIC indication check charging system if it fails
Not if it is charging at low amps as they often do.
A load test would show voltage and amperage but it does not tell much if the intermittent failure is not happening during the test. I frequently see a car that has dead battery complaint no alternator light. I load test the alternator and find the output is only half or a third of the specification. I proceed to replace the alternator and battery if the battery is bad too. Frequently the battery is damaged after going dead several times.

glake89
05-09-13, 01:27 PM
2 50A fuses for each side.

orandaberg
05-09-13, 01:31 PM
Thanks
Apparently I have no battery issue because I left it unhooked and the mechanic went to pick it up and it started right up.
Th BCM an ECM apparently control the amount (I think) of out put the alternator works (I read about it but cannot explain)
So your saying the alternator can test and even under load but be bad
Hmm I guess since the whole front end is off, it easier to get to the alternator, so maybe to double check is to remove it and take it somewhere to be tested, too late now, it would be 10 days to get a new one

orandaberg
05-15-13, 05:33 PM
No more unsteady reading now that the belt has been changed:)

Mr.electric
05-18-13, 12:12 PM
Wow. Unusual solution. Belt was slipping?
I would think that it would make a lot of squeal noise in the morning if it was slipping.
Maybe a loose ground got tightened during the service.

orandaberg
05-18-13, 12:20 PM
Gremlins. You do have a point this car has/had corrosion problems.