Question about 2002 Lexus RX 300

1 Answer

Battery keeps draining when car sits for several days.

Battery discharges when vehicle sits idle for several days. I have replaced the battery, alternator, dome light, and door switch all in the last 4 months. The car is still discharging the battery. There is a low voltage drain somewhere in the vehicle, but where? It appears this is a common problem in these vehicles as I have read about other vehicle with the same issue. HELP PLEASE!!!

Posted by on


1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Lexus Master
  • 5,488 Answers

Try this to see if you can find the drain: Wait until the car has been off for a half hour, so computer is in sleep mode. Open hood and remove underhood light bulb. Take off negative cable from battery and hook up a test light between cable end and battery post. If you have a drain, bulb should be brightly lit. Start removing fuses one by one until light goes off. When a fuse is pulled that turns light off, that is the problem circuit. Check everything on that circuit to find what is staying on.

Posted on Jan 23, 2013


6 Suggested Answers

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

A 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
The service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
Good luck!

Posted on Jan 02, 2017

  • 7 Answers

SOURCE: battery drains overnight

some time the radio will put a drain on the batt. if it has a short. pull the radio fuse, charge the batt. and let it sit over night to see if it drains.

Posted on Jan 02, 2009

  • 3 Answers

SOURCE: I suspect a weak battery, but how do I know it's not a bad ALT?

when your car is running disconnect the positive cord from the battery. if the car stays on, than it is your alternator, if not its your battery. also if the car stays on, the head lights go dim if the alternator is malfunctioning

Posted on Mar 18, 2009

  • 450 Answers

SOURCE: front dome light always on and drains battery

switches go bad in the doors. Easy to replace, fairly cheap.

Posted on Nov 17, 2009

  • 166 Answers

SOURCE: 1990 lexus ls 400 security system went off now

Okay you may want to check to see if the sensor on door lock cylinder hasn't fallen off from the lock itself. Pull of the door panels and check the wires at the door lock cylinder. Hope this helps.

Posted on Mar 25, 2010

  • 2382 Answers

SOURCE: son (college student/part time

Hi, causes of excessive current drain from a car battery include things like lights that remain on (trunk and hood lights, interior lights, brake lights, etc.) and also relays that may be stuck on, or modules that are not going to sleep or powering down. A fuel pump relay that sticks on may keep the fuel pump running after the engine is shut off. A switch or relay that powers a rear window defogger can stick on, pulling current from the battery after the ignition is off. An electronic suspension module, ABS module or keyless entry module may remain active long after it should have powered down.An accessory such as a DVD player, game console or cell phone charger left plugged into a rear seat power receptacle may be pulling power from the battery. So before you spend a lot of time trying to figure out where the amps are disappearing, check all of the vehicle's power receptacles to see if something is plugged in that may be using power.


If the key-off current reading is above specifications (typically, more than 50 mA one hour after the vehicle has been shut off), the current drain is too high. It's time to start pulling fuses and relays to find the fault. Refer to your vehicle owner's manual or a wiring diagram to identify the fuses and relays. Then pull the fuses and relays one at a time until the current reading drops. Avoid pulling the fuses for the PCM or other KAM-sensitive modules until you have checked all of the other circuits.
Once you've found the circuit that is causing the excessive current drain, check the relay, switch, module or other components in the circuit and replace as needed.
Sometimes a bad alternator diode can cause a car battery to run down. A good diode should only pass current in one direction. If it leaks current in the opposite direction, it may keep the charging circuit on when the engine is not running, causing the battery to run down.

Posted on Oct 06, 2010

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

92 Saab keeps dying, won't hold charge....

You have the battery and the alternator and the alternator belt and if they are working fine there must be something that is draining the battery. You need an auto electrician to check what the drain is. In such cases,on various vehicles, the BCM, body control module, proves to have something to do with it. Get A GOOD AUTO ELECTRICIAN to check if there is a particular component
draining the battery

Jul 18, 2015 | Saab Cars & Trucks

2 Answers

Battery tested

sound like alternator has bad diode allowing battery discharge

Oct 16, 2013 | 2009 Pontiac Torrent

1 Answer

Electrical system drains battery when vehicle not in use

Normal for a 3 year old battery. it has internal resistance that discharges it self.

Disconnecting the battery will not help.

A way to see if vehicle is causing the discharge,but it will dump the radio and clock settings....take off one of the battery terminals and put a test light (12 V.) between the terminal on the battery and the cable end. If the test light comes on,there is something ON in the car.

If the computer memory is dumped due to low voltage,the car has to "re learn" all of it's setting and will usually not idle well at all!

Please have the battery load tested after it has been fully charged.

Dec 25, 2012 | 1998 Oldsmobile Bravada

1 Answer

The battery keeps running down when the car sits idle for a few days. The alternator has been tested and verified to be in good working order.

most obvious cause is a diode in teh alternator but it could be the boot light thats another favourite ,or just the battery is sulphated up and needs desulphating as follows -discharge battery with 6 watt bulb when completely flat put on a trickle charge ,when fulkl discharge again and then recharge ,4/5 times and the battery amp hour capacity will improve ,then it will take a month to go flat which is about right on a modern car unless it has a shut down mode ,

Nov 24, 2010 | 1998 Buick Riviera

1 Answer

I have a 2007 GMC Envoy. I've had to jumpstart the SUV for the last 2 days. Could it be the battery?

Either the battery, the battery cables/connections, the alternator or alternator cables/connections (in the extreme a drain could cause battery discharge). Have battery tested. Look for signs of corrosion around cables. If vehicle won't start after sitting but will restart when turned off, suspect battery. If won't restart after driving, suspect alternator.

Jul 09, 2009 | GMC Envoy Cars & Trucks

1 Answer

When we turn key car is dead. Car has been sitting for 2 months.

replace your battery, a battery discharges every day you dont run the alt. to charge it up... after a week or 2 weeks the battery would be dead, just from a car sitting not being started... if you are not using the vehicle, it is a good thing to replace the battery, and every couple days just start the car up and let it run a while to charge the battery.... if you are going to have to leave the car for a while without starting it, then disconnect the battery, and remove it from the vehicle... you can buy a cheap trickel charger for the battery when it is out that will keep it charged till you decide to put it back in.... hope this helps you...

Jun 14, 2009 | 1999 Volvo S80

1 Answer

Engine keeps dying after I turn it on.

I had the same problem when I did battery maintenance on my 1988 Montero Sport. The problem was explained to me, that the car's electronic pollution control computer data was erased when the battery is disconnected or the battery totally discharges. The car's computer uses this data to regulate idle speed and other engine factors. The solution given to me was to recheck the battery connections (make sure they are clean, and tighten down), start the vehicle, and just let it sit and idle for about 15 - 20 minutes (without racing the engine or driving the vehicle). This will rebuild and repopulate the car's computer engine data it needs to make adjustments. Hope this helps.

Jul 15, 2008 | 1998 Mitsubishi Montero Sport

Not finding what you are looking for?
2002 Lexus RX 300 Logo

487 people viewed this question

Ask a Question

Usually answered in minutes!

Top Lexus Experts


Level 3 Expert

79186 Answers


Level 3 Expert

918 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22326 Answers

Are you a Lexus Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides