smokedawgs

i have a 99 rx300, the battery has been dying on me randomly for the last while, i disconnected any aftermarket products i had installed and i'm still running into this problem. so my mechanic started to check if there was a drain on te battery, he shut of the engine, disconnected the neg terminal and put a voltmeter between the neg terminal and the negative battery post. there was voltage so he started taking out fuses from the fuse box in the engine. once he removed the DCC short fuse the voltage went to 0, and he said whatever that fuse does is draining my battery overnight. i cant find it in the manual or anything and the fuse looks good, does anyone know what its for or what is causing the drain??

the wierd part is that sometimes my battery will last a week, then suddenly die 3 days straight overnight....as long as i keep driving the car the engine starts fine, it only seems to die overnight. any help pls!!

bob2200

I don't think your mechanic sounds too savvy with electrical stuff. There are a number of things in modern cars that draw a small amount of electrical current all the time (e.g., the clock). You need to measure current flow (in amps or milliamps) from the battery and then figure if that is enough to drain the battery in several weeks. Of course, you need all the doors closed (i.e., door lights off) during this procedure. Even 100 mA (0.1 amps or 1.2 watts) is just 2.4 amp-hours per day, which isn't that all much.

If you still are using the original battery, that explains it.

mikey00

You may want to do a search on "battery". If I remember correctly others have changed the Body Control Module to fix this battery drain problem. You first need to determine what a normal current draw is. The only way I know to do this is check another RX. As bob2200 already said, if you still have the original Panasonic battery just change it.

smokedawgs

yea he didnt seem too bright, okay well i will try to get the voltmeter and as much info as i can as to what fuse and how much volts/amps or whatever the little machine tells me and i will hit u with a post soon!! pls check back and help me out! thx!!

mikey00

What you need is an amp meter. One of the battery cables gets removed and the one amp meter lead gets connected to the removed battery cable and the other lead gets connected to the battery post so that the current actually flows through the meter. With the key removed this will indicate the current draw. If you know the current draw on another RX, you have something to compare too. After reading your post on another site, it looks like your mechanic didn't have an amp meter and attempted to use a bulb and determine the currrent draw by its brightness. This is a little crude but should work somewhat.

code58

This is not directed to you Mikey-I just quoted you because you were the last poster.
You don't really need to remove the battery cable if you have an amp clamp- though it would be good to have a highly sensitive one. I have 4 different ones - each has their specific use. As for the mechanic that used this method to determine the draw on different circuits- I don't know that mechanic or his abilities but don't be too hard on him- I have known some very fine professional mechanics that use that method and use it myself from time to time. You quickly learn from the intensity of the light just about how many amps (or probably milliamps) the draw is. I can tell you within about 100 milliamps or less what the draw is from the intensity of the light. And I normally use an ampclamp. It is a very usefull tool for someone who is not a professional mechanic and does not have a meter or amp clamp. It's very quick and simple AND effective.

mikey00

Good point on the clamp on amp meter. I guess I am starting to show my age when I talk about inserting an amp meter into the circuit rather than just clamping on. In the past clamp ons were always kind of pricey unless you were in the business. But the price has come down a lot lately.

salimshah

Good suggestions on how to measure, but no one has posted what are the reference (good) values.

Remember to turn the auto lights switch off.

Salim

thomas1

Salim, got time, take yours apart and make a spread sheet and gives us the currents....Just kidding, I was considering, maybe when I do my next major maintenance.

mikey00

Anyone with a clamp on meter should be able to provide a good reference # in less than a minute without taking anything apart. I don't want to pull a battery cable and reset things using my inline meter. code58 maybe??

salimshah

Fair enough but I don't have one those clamp-on meters.

Nobody mentioned the elephant and I was concerned that the original poster will be scrambling to get the instrument to find out that the reading is of no use.

Salim