Hi, ref 2002 S 60 with 2 year old battery: the battery tests good (takes a full charge and holds it well if not connected to the electrical system of the car) and the alternator is generating 14 volts to the battery (measured at the battery terminals) THus I have to rule out a battery problem or alternator. Does anybody know what the electrical system should draw (amps) when the car is totally shut down?? Anybody experience this problem, like what part of the electrical system did you find that was drawing too much on the battery (or more than zero when that section should be zero draw). Albeit the computer system draws a very small amount of current, not enough to drop the battery voltage in almost 1/2 over nite . Thanks

 

Don't assume just because the alternator is supplying voltage it is good. It may have a short to ground and still produce voltage. Likewise, there may be a short to ground in the cabling. I would think that an object that is draining a known good battery overnight would be giving off some heat. A properly functioning electrical system and ECM draw very little amperage when shut down.

 

I am having a similar problem and I think I have narrowed it down to the alarm siren module on my s80.. Does yours work fine? Mine has been giving trouble so maybe it drains down the car while I'm not there...

 

you have a parasitic draw draining the battery. You''l need a multimeter to dig for the culprit.

Has any electrical component been acting up lately? If so, I would start there.

 

Thanks to the several responses above. I have checked all the bulbs to see if any are on when shouldn't be (vanity mirror, dome, glove box, trunk) and all are fine. But, the voltage drop is very quick, about 4.5 volts in 12 hours, so it is a fairly high current draw. today I will
be putting an ammeter into the battery circuit and then pulling the higher amp fuses first to see what stops the draw of current. will start though with the alarm fuse as that seems to be a fault area somewhat common. thanks again.