My 2000 RX has the same issue, very randomly and very infrequently, happened maybe 4 or 5 times over nearly 20 years in recent years. Every time it happened the battery terminal voltage was 4 ~ 5V.

I have a DC current clamp meter to measure the current draw at battery positive terminal where it has just enough room to put clamp meter on. However, even if I close and lock all doors, the hood is open, so the computer will not go to sleep?

Not like some other cars under the hood there is a push switch to tell computer whether hood is open or closed, I don't know how to cheat the computer that hood is closed for valid current measurement.

By the way, my driver side master door switch was replaced with a genuine Lexus switch many years ago. It was for door locking not battery draining issue.

 

Did you ever figure out how to make the computer think the hood is closed? I'm trying to track down a parasitic draw that started recently in my 1999 RX, with about 50K miles (not a typo).

 

It used to be actual switches controlled things (Hood/Door depressed a pin connected to a switch), but nowadays most cars have sensors on the LATCHES so if the latch is closed, the computer sees it as the panel is closed even if it's open.

Just remember to unlock the latches before trying to close the panels!

 

A few months ago, my battery died. I had it replaced, & after about two weeks, it was dead. Back to the dealer, got another new battery, two weeks later it died again! This happened 3 times! Dealer days he checked the alternator, starter, all the usual suspects. They can't find the problem. My SUV is currently sitting in my garage, dead again. Anyone have suggestions? Please help!

 

If the vehicle is being repaired by the dealership then they are responsible to find the problem. You have paid them and they should fix it.

Battery problem are due to battery itself, charging system and drain. If you do not drive the vehicle enough then the charging time may not be enough to recover the loss during starting.

Once the vehicle is turned off and locked, the drain is reduced in stages and it never goes down to zero. You can hook up an amp meter (VOM setting + connection) to see what is the drain. For more detailed discussion please search on "parasitic draw".

You can keep pulling fuses to take circuit off line to see which sub-circuit is pulling the current.

Salim

 

I hesitate to say Ive completed my repair of the same problem but wanted to give information that may help you. I had researched this for a while, taking my time as the rx300 wasn't on the road yet. I found both circuits, ECU-B, and the dome - c was drawing power by testing across bat terminal and the disconnected negative cable. I had my alternator tested by AZ, but they couldn't test for parasitic draw. I saw a video on u-tube about ohm testing the power lead to check diodes, mine never passed the ohm test and I was always suspicious of the alternator even though mine passed AZ test. I ordered a new diode pack and regulator for it since it seems to be in good otherwise. after replacing it, I had an ohm reading in one direction like the video said. Knowing the dome circuit was part of the driver's door ECU, I purchased a used door control. Not completely sure if it has cured my issue yet but will test the system today.
I also found (on here) that one person spoke up because they found no completed answers, the blogs where just dropped and no conclusion, so he concluded that his was the driver's door control ECU and his alternator.

 

Doing an Ohm test on my alternator, it registered ohms either way, + or - so I ordered a diode set and regulator which cured the alternator ohm issue and a door window control since unplugging it reduced my draw. Hope this helps.
Well, this wasn't the issue after all.

 

One issue I had on my RX was an old lojack device that was sapping the battery.

 

I havent read this before but it sounds like a probable solutuion. I will look today, fingers crossed as my door window control and new diodes in the alternator didnt work.

 

I ripped my dash apart today and didn't see any taps into the stock wiring. I also removed dash items and unplugged them as I went while watching the meter which was monitoring the voltage across the neg term and cable. Nothing seemed to change, then suddenly it read 60ma, so I plugged things back in, it was at 60ma then suddenly it went to .55 amps again. Lost again!

 

Instead of getting into the dash, start by the pulling fuses.

Turn the headlights off [not auto]. Monitor the current by placing the meter where you can see it from the cabin. Remove the key from the ignition. I would start by locking yourself in the cabin and do double click remote lock. See the vehicle go to sleep in two steps. Then start pulling one fuse at a time. You can put them back if the current draw does not change.

Salim

 

Hi-
The battery drain problem disappeared for a long time on my '03 RX300 I started this thread with 4 years ago, but now it's BACK. My battery stays up for
maybe 2-3 weeks one time, but is dead in a few days another. Obviously this is not a car you can leave at, say, a valet parked airport parking lot where
you can't disconnect the battery while away.

Sometimes the battery stays fine for a week-or two days, and other times it goes flat in a few days, which is MOST frustrating.

The ODD thing IMO is that I suspect most modules stay active down to a certain voltage and probably drop out (total conjecture
on my part) and stop drawing current, leaving the battery at whatever voltage the drain dropped out at.

But my battery measures about 2 1/2 volts as did another poster above. A continuous draw (like a resistor) would draw the battery to zero (eventually) rather than something like 2.5 or so.

Since this returned this summer, I leave a float charger on the car, but it's clearly a PITA.

Someone mentioned a bad alternator diode. I guess you disconnected the battery and used an ohm meter, reversing the leads after each measurement. It should show continuity one way on the test leads, and infinity the other way around unless a diode is shorted, in which case it will show continuity (low resistance) both ways?

Did someone verify latching the hood latch tricks the hood-open-switch to the closed position?

With regard to the driver's door window switch, if it is bad, what are the symptoms? Does a light stay on or anything? The only light I see with the doors closed (not locked)
is the Security Light flashing when the door is closed.

We've had the vehicle for 10 years now, and it only has 55,000mi, so it doesn't get used daily (even less in the pandemic), so it would be nice to be able to get a couple or three weeks on the battery and still have the car start. If the battery is 90 amp hours, to drain the battery half way (leaving 45 amp hours to crank the engine) would be 1 amp draw for 45 hours, or .1 amp (100ma) for 450 hr (18 days) or .05a (50 ma) for 36 days if I did the math right.

I guess it's back to the drawing board to start the search (again).

 

Oh good, I get to type this again because it timed out on me.......ugh! My assumption was incorrect, I thought it was my door control, bought a used one, and retried but didn't seem to make the difference so I started unplugging everything I could... radio, heater, display, cd changer, relays, etc.. When done suddenly the voltage draw went from .55 amps to 60ma, hurray! But still skeptical, I plugged all back in while watching the meter. Got done and was at 60ma but it went to .55 amps again in a very short time. Still no good results. The good thing is that this is an extra vehicle so not dire, just extremely frustrating. It seems like the ecm not sleeping is the hidden reason but I cannot prove anything at this point.

 

I did the fuse pulling out of the car but not locked, I found the typical fuses for dome and ecu-b are the circuits connected with the draw. I will try your idea and get back to you. Thanks!

 

Sorry Salimshah, I replied kind of out of order here. I looked for a lojack type device spliced anywhere and saw nothing that looked aftermarket. Where was your LoJack located?