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Parasitic battery drain - pulled every fuse and still can't isolate


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2005 RX330.

 

I disconnected the negative terminal and put a light bulb in between the cable and terminal.  It's shining very bright, indicting significant current draw.

Went around to every fuse under the dash and engine compartment.  Also disconnected the alternator main cable as well as wire harness.  The light stayed on continuously and never even dimmed.

Is there something/somewhere else I should be checking? 

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Just tried a different battery to rule that out... nothing.

 

IS there some part other part of the electrical system that's not going through the fuses?   I would think any kind of a small short on the unfused part of the +12V main wiring would cascade into a full blown short pretty quickly.

 

 

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Not everything goes through those fuses. There are certain wires called, "fusible links" that are designed to melt like fuses, but look just like regular wires. These vehicles have numerous computers and receivers that need to stay powered in standby mode. Otherwise, when you went to start your car and turned the key, you would have to wait for the engine computer to boot up so it would know how to run. Also, there are antenna receivers that are always in standby just waiting for you to hit the unlock button on your key fob.

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understood on the fuseable links.  But those are typically designed to protect circuits with high transient inrush currents.

There's something that's pulling a significant enough current to brightly light the bulb and even generate sparks when I go to connect the cable back up.

Put an ammeter on it and it's pulling 600 mA.   That's a lot of current drain...

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Interesting... watching the ammeter...

It starts out at 600 mA, then after 10 seconds it drops to 250 mA.    Consistentyly does this... I hook up the ammeter, starts at 600 mA.... then after 10 seconds, drops to 250 mA.

 

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ok, now I'm realy scratching my head...  

after 2 minutes it drops to 25 mA.   That seems within the realm of being nominal for this kind of car.

SO maybe it's just the battery is not holding a charge... which is odd since I think it's only 2 years old (a Bosch).

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