Alternator, battery, or ground issue?

[lemoose]

A couple months ago- the DSC light turned on and wouldnt go back off until i restarted the car. This has since happened several more time in the recent weeks- Along with the car also being completely dead every other time i try to start it (i only drive it about once a week or so). At first i figured it was my 4 year old battery which i have now replaced- and figured that was the obvious cause of my problem. However the car was completely dead today as well. Id figure the next best guess would be the alternator but this was replaced 5 years ago with a bosch part- although i assume i cant rule anything out at this point. Below are my voltage readings (both engine running and off). Any ideas whats causing this?

[sapote]

13.3v running is low but DME measured could be lower than measured at the battery, and the battery could be discharged too low causing a low charging voltage.
should have car running for at least 20 minutes, then measure at battery with voltmeter.
I would charge the battery overnight, the check its voltage after remove the charger and wait 30 minutes.

[lemoose]

13.3v running is low but DME measured could be lower than measured at the battery, and the battery could be discharged too low causing a low charging voltage.
should have car running for at least 20 minutes, then measure at battery with voltmeter.
I would charge the battery overnight, the check its voltage after remove the charger and wait 30 minutes.

Yea the battery was completely dead- i drove around for about 15 min and the readings above are what i got. Ill put a couple more minutes and miles on it tomorrow and see if that changes anything- ill get my hands on a voltmeter and report back- but doubtful i can get a charger

[sapote]

If the car was able to crank and start on its own battery, then the ground connection is ok.

[FBloggs]

Sounds like intermittent charging activity from the alternator. Could be worn brushes or a dodgy diode.
To rule out a dodgy battery, it needs to be tested to see if its voltage collapses under load.

[lemoose]

Sounds like intermittent charging activity from the alternator. Could be worn brushes or a dodgy diode.
To rule out a dodgy battery, it needs to be tested to see if its voltage collapses under load.

See that would sound likely except that my battery will also die within a week if i dont turn the car over- which im not sure, but i think that points more to a ground or battery issue. So long as i keep using the car i have no issues

[FBloggs]

See that would sound likely except that my battery will also die within a week if i dont turn the car over- which im not sure, but i think that points more to a ground or battery issue. So long as i keep using the car i have no issues

My car has a 5yo battery that is down 200cca. It's on borrowed time.
But it will start the car easily after 10 days of non use.
you have a new(ish) battery yet it won't start.
Either it is not getting the correct charging voltage...poor alternator, or not enough running time for the alternator to charge it fully.
or,
you have a voltage drain.
Your charging system needs to be tested.
If the car starts at all, there is no issue with the grounding to chassis.

[sapote]

It could be that car was not driving enough for fully charged battery, especially with SMG which used more current whenever trunk, doors, hood opened/closed. You need a charger to save money on buying battery. Battery has short life if not fully charged.

[lemoose]

Sorry for the late update- below are my readings after driving around for 2+ hours. First pic is before starting, second is with the engine running. A couple anomalies to note that also occurred on the lead up to this issue are that at times in recent months my dash and console lights would flicker if i even just so much as touched the lcm knob, also one day my aftermarket headunit (xtrons) was bugging repeatedly turning itself off and on. This only happened once but i guess the dubious nature of the manufacturer would be enough explanation- i just think its worth mentioning because it happened around the same time my lights were acting up

[Shonky]

Both pictures are showing 0 rpm

[lemoose]

Both pictures are showing 0 rpm

Thanks for catching that- i updated the post with the correct pics

[sapote]

Sorry for the late update- below are my readings after driving around for 2+ hours.

The first pic shows 11.8v measured by DME (which means real battery was about 12v), and it was low. You should keep the battery charged up -- 12.6v minimum -- or it will be ruined soon. This also placed a very high load on the alternator when engine first run and charging the low discharged battery, not good for alternator.

Second pics with 13.8v which means battery was about 14v. This shows alternator and cable/connector, up to the battery cable but not the battery, are all good. However this doesn't mean the battery was charged at 14v, because the DME only measured the voltage on the cable, regardless if the cable to battery connection was good or not. The sure way is to measure directly on the battery posts using voltmeter.

[lemoose]

The first pic shows 11.8v measured by DME (which means real battery was about 12v), and it was low. You should keep the battery charged up -- 12.6v minimum -- or it will be ruined soon. This also placed a very high load on the alternator when engine first run and charging the low discharged battery, not good for alternator.

Second pics with 13.8v which means battery was about 14v. This shows alternator and cable/connector, up to the battery cable but not the battery, are all good. However this doesn't mean the battery was charged at 14v, because the DME only measured the voltage on the cable, regardless if the cable to battery connection was good or not. The sure way is to measure directly on the battery posts using voltmeter.

Thanks- dont mean to be stubborn ill have measurements with a voltmeter once i get back from vacation. Its just been eating me up and i already had these from earlier lol. Really sucks though that my new battery is actively ruining itself on me while im 1000 miles away lol oh well

[lemoose]

Probably another important piece to the puzzle i hadnt considered. Heading back home after getting the new battery, my window regulator failed- so i got home and parked the car for about a week until i got the replacement and installed it. The car did start right up afterwards, however, but i guess it wouldnt be far fetched to assume that i may have never given the new battery a chance to properly charge and hence may be running less then optimally

[lemoose]

alright got back from vacation and got the multimeter in. i guess its time to start pulling fuses?

1. car was dead upon returning and I had to jump it. drove it around for about 15 miles- turned the car off and waited an hour. battery measured at 12.33
2. cranked the engine and voltmeter read 13.8 at the battery
3. turned the car off after about 5 minutes, removed key from ignition. reading was 12.47