2008 Lexus RX 350

Looking for help in troubleshooting a problem with battery draining after 2-3 days if car is not started. New battery and charging system checks OK. Have had to replace the battery 3 times in last 2 years, and twice in last 5 months.

Troubleshooting completed

Used ammeter between negative battery cable and negative terminal to measure current. With all fuses in, current starts at ~680ma, drops to ~320ma after 1 minute, drops again to ~110ma after 5 minutes, and finally drops to ~80 ma. The current stays at 80ma most of the time, and occasionally drops to ~60ma.

Started pulling fuses one at a time. Only 2 fuses affect the current.

ECU-B, Fuse 24 (7.5 amp) under hood. Has several circuits - power window, multiplex communication system, gauge and meters, instrument cluster lights, air conditioning system, garage door opener, illuminated entry system, power back door, driving position memory system, navigation system display, moon roof, tilt and telescopic steering, power seats, outside rear view mirror, windshield wipers.

When ECU-B is pulled, current reduces to ~60ma

ECU-ACC, Fuse 28 (7.5 amp) under driver side dash. Circuits on this fuse - navigation system display, power rear view mirror control, shift lock control system, multiplex communication system.

With ECU-B and ECU-ACC pulled, current goes to zero, so ~60ma on this fuse.

I exercised all switches and checked to make sure that lights, etc. were off when the car is powered down - all looks OK.

1. What should be the normal current after car systems power down? Is 80ma normal?

2. Any ideas on what components are most suspect to cause problem?

Thanks for any help on this!

 

Many cars I've tested are between 60 and 80 milliamps doesn't sound like there is anything wrong with your RX. 80 milliamps is 1 watt just about any battery should be able to maintain 12.4+ volts for at least 30 days with that kind of draw. If batteries keep dying I would look closely at the charging system, the cables, grounds etc.

 

Thanks, Lexus2000. A shop checked the charging system, so I have not looked at it myself. Will check it out.

 

Hook up your amp meter and let it be for several hours keep checking. Sometimes modules act up randomly although not usually (or maybe ever) on a Lexus.

 

I watched the ammeter for a while after powered down to 80 ma, and also left it connected for a couple of hours and checked it periodically. Did not see anything “wake up” but could have missed it. When I remove the ammeter and reconnect it, the system does “wake up”, as the current increases to ~600ma and then reduces back to 80ma after several minutes. Unfortunately, I do not have a meter that records or saves max value.

I did check to see that some of the circuits on these fuses are switched and power down with the ignition switch, and would think that eliminates many of the circuits on these fuses.

 

Also, with respect to the charging system, I am able to reduce the current flow to zero by removing the two fuses listed in the original post. If the alternator, cables, etc were the problem, I expect that I would still see a parasitic drain - am I thinking about this correctly?

 

The alternator always gets power, at least part of the unit. Your thinking is right.

 

Where is the key fob when the car is sitting? If its within 25 ft it may communicating with car causing both fob & car battery to energize and constantly discharge. Don't forget about the extra key hanging by the garage door.

 

This is an older car and the key does have buttons to lock/unlock, etc. I believe the battery is dead in the key as none of the functions work. I have checked the current with the key near the car and away from the car and there is no difference. When I did extended testing, the key was in the house, not near the car. Thanks for the reply.

 

I'll 2nd this...
These numbers look within spec and similar to my RX330 with no parasitic draw issues.
If there is something failing intermittently these can be the hardest glitches to track down.
PS- compliments to OP for an excellent job on explaining the complaint and what was done already.

 

There may be an intermittent problem, and I haven't been there when it occurred. I plan to get a clamp on ammeter with high/low memory and see if something this detects a high intermittent draw. I appreciate the help from everyone.

 

Ever find out what the problem was? I’m having a similar problem. Thanks.

 

Me too!

Any final updates, @imintenn ? I have my fingers crossed your excellent sleuthing and observation skills might give us some guidance.