Lexus RX 400h: Problems & Solutions



  • katzjamrkatzjamr Member Posts: 146
    For many with these vehicles the 12V battery has been a week link. I love my 400h, however many have reported early problems with the OEM battery. Once it goes completely dead it may never be reliable. I would have it checked for the ablility to hold a charge and its general health. Have the dealer replace it if its questionable. Also more importantly any time your 12V battery goes dead make sure the dealer reprograms your 400h. You may notice lower than average gas mileage until this is done. Believe it or not non functioning items like the sunroof and the windows are a symptom of a bad battery in this lexus.
  • lxpatellxpatel Member Posts: 34
    Thank You,

    I have not noticed any changes in Mileage, but all the radio presets and Avg MPG in the energy menu have been resetted. Do you really think it needs to be reprogrammed? And if so what do they reprogram?
  • kjoebkjoeb Member Posts: 2
    Interestingly enough, my 06 cruise works great on the hills on I44 in SW Missouri. MPG is poor to say the least, but the cruise is good. Strange Lexus is saying that is functioning as designed (FAD). I don't think there is an engineer anywhere that would do that on purpose.
  • Kirstie_HKirstie_H EdmundsAdministrator Posts: 11,126
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  • lxpatellxpatel Member Posts: 34
    I just had the Auxiliary battery replaced at the dealer, they put 84 month 500 Cold Cranking Amp battery, i wanted to find out what CCA came from the factory if any one has a RX 400h that has not had the Auxiliary battery replaced by the dealer.
  • wwestwwest Member Posts: 10,706
    You may have made a mistake, a big one.

    The 12 volt battery in your RX400 is kept charged via a voltage downconverter/inverter from the hybrid battery.

    Too much battery loading, battery too big, might destroy the downconverter.
  • lxpatellxpatel Member Posts: 34
    Well, Lexus installed the battery, and 8 yr warranty plus Lexus extended warranty to 100k, hope fully downconverter is covered item.

    One other note.

    They did reprogram something which made the rear power windows work from the driver's door switch as well as the roof which started to function properly
  • drgkjedrgkje Member Posts: 21
    just got a new 400H. one of the scary things the salesman said is that if you run out of gas, you cannot just add gas, restart and carry on...the car has to be towed to the dealer. did not find any such statement in the manual.

    anyone has any experience or info?

    btw, love the car, rides great, a couple unusual feelings and noises but we were prepared as had read about them in this forum
  • varixvarix Member Posts: 72
    I have a 2 month old 400h with 2K miles on it and today the rear door would not open electrically, rather it stuttered and made a grinding noise and then stopped after a few seconds. It did this 3 times but later in the day it worked OK. it could always be opened manually. Any one with a similar problem/solution?
  • katzjamrkatzjamr Member Posts: 146
    it is true that you do not want to run out of gas with this vehicle. what will happen is you have three chances to start the car after running out of gas. if it does not start after the third time, it will electronically shut down to protect the main battery. it then will have to be towed to the dealer to be reset and started. the reason for this is to prevent people from operating the car on electric only when there is no gas in the tank and the engine cannot run to support the battery. toyota is preventing you from possibly ruining the main battery and needing expensive replacement. also for most cars the fuel pump is in the gas tank and fuel surrounding the pump keeps it cool. when you run very low consistently in can cause you to need to replace that pump sooner. when the low fuel light on the dash lights up, you have about three gallons left. i used to be one of those who ran low on fuel before filling up. i dont do that with this vehicle.
  • drgkjedrgkje Member Posts: 21
    Thanks for the detailed explanation. I have to tell the family to WATCH the gas gage.
  • hilandr05hilandr05 Member Posts: 18
    Only 500 miles on my 400 so I have not gone back to the dealer yet. Before I do, I wanted to check if anyone else has experienced this.

    At speeds over 30 MPH there is s noise coming from the back that sounds a little like a metallic fluttering. I thought it might be a tag or something loose underneath, but nothing found. With someone in the back seat to help listen, it seems to be narrowed down to coming from under the seat, which would mean possibly something in the battery area. Could it be something with the battery ventilation operation?
    Anyone else have a similar experience?
    At speeds above 60 the road noise takes over and most of the time I cannot hear it. So I know, the solution is to drive fast!

  • hilandr05hilandr05 Member Posts: 18
    500 miles on my 400 averaging 28 MPG
  • roycrawfroycrawf Member Posts: 4
    On our Highlander the license plate was fluttering. On the RX400 the latches for the self retracting cover were rattling. Took a while to find both. For the latches, just push them down into the latched position when the cover is not installed.
  • mkkidmkkid Member Posts: 11
    It took my more flexible son contorted in the luggage area of my 400h to find this same rattle. It's exactly what you found and repositioning the latches stopped a noise that drove me nuts for an entire 4 mo vacation trip!! Told my dealer, but they seemed amazed like no one else had ever complained about it.
  • lexrexbluelexrexblue Member Posts: 38
    The dealer installed some little adhesive sound insulators on my latches. It seems to be working. They heard the sound, too.
  • andyskiandyski Member Posts: 2
    Just got my RX back from the dealer yesterday. I brought it in for (among other things) the same issue. Mine turned out to be an exhaust system heat shield under the vehicle, which I suspected originally. That's why you hear it from the battery vents: the soundproofing probably isn't as thick there. They "made an adjustment" and now the sound is gone!
  • colomarkcolomark Member Posts: 3
    Is there any chance you can provide contact information for the dealer that fixed this? My RX400 does exactly the same thing and beyond adding some insulation on the battery vent sheet metal they have not been able to identify the problem. Maybe I can get them to call your dealer. The battery did ratle, but the main noise changes with the wind so I knew it wasn't the only problem.
  • andyskiandyski Member Posts: 2
    No problem. It's Hoffman Lexus in East Hartford CT. Their web site is While I was there I asked them to do the ISC learing procedure, since my mileage was only averaging about 21.5 mpg with mixed city/highway driving. They did the procedure and my mileage increased by approx. 2 mpg. I noticed that the electric motors run a lot more now, especially once the engine heats up. Good luck with your issue!
  • wwestwwest Member Posts: 10,706
    that if the need for the catalyst being kept up to temperature is the reason the ICE needs to be run more often/longer than otherwise why not provide a good insulation jacket for the catalyst such that it does not cool so rapidly.

    The only shortcoming I can see would be the possiblity of overheating the catalyst when the ICE is REQUIRED to run continuously. Seemingly that problem could be easily overcome via the activation of a blower system to reduce the overheating probability.

    More weight and complexity but that would be more than overcome by the improvement in FE.
  • hilandr05hilandr05 Member Posts: 18
    Thanks for the great info Andy!
    I went to the dealer to pick up my registration paperwork (things are a little different in Florida) and I was going to have them look at the noise. On the way there, I could not hear the noise, so I didn't take it to service dept. Of course on the way back on the turnpike, there was the noise.
    So I followed your information and sure enough, the heat shield. It is just thin metal and is secure on the outboard side. On the inboard side it flexes and is close enough to the underside of the car that certain wind conditions cause it to flutter and make the noise. I bent it down slightly and no more noise. When I take it in for first service I will see if they have something to make it more secure.
    If they don't have it, sounds like (OK, pun intended) they need a service bulletin on the problem.

  • stevedebistevedebi LAMember Posts: 4,098
    You are suggesting adding insulation to the converter and then going to extra lengths to cool it down. That is a lot of complexity.

    However, this still would not help the short trips, since the converter still has to warm up for the first time...
  • colomarkcolomark Member Posts: 3
    Thank you. I really appreciate it. Let's see if they can fix it tomorrow.
  • colomarkcolomark Member Posts: 3
    From what we can tell after a few days of driving the car in high wind conditions the dealer fixed this noise. It ws the heat shield. Thanks for your help convincing them I wasn't nuts since they did not hear it in their noisy wind free city location.
  • lexus400lexus400 Member Posts: 8
    Please do call Lexus. I have been dealing with a gal at Lexus and they are the ones that wanted a return test drive with the service manager and then the district manager. When this started, they told me on several occasions that I was the only one with this issue. They need to hear and have it docummented that other people are having this same issue. To date, they are unable to provide solutions. If I had felt this on a test drive-of which they did not have a 400h to test drive, I would not have ordered. When I did return with 500 miles, they told me there was a solution in the works--hope it just wasn't to get me past the 30 days when I could have returned the car.

    Keep us all posted! I don't want to sell the car as a used car within 6 months of purchase.

  • answersanswers Member Posts: 1
    I have also had this problem. Acquired my vehicle in 7/05 and thought it was just the heat of the summer and the A/C. However, since the winter months and not using the A/C but using the heater, the smell is still there. It smells like hot water musty and moldy. I have had it in the Lexus dealership at least 4 times since I purchased and they still cannot find the source. We tried the A/C recirculation button on and did not make a difference. We have asked our dealer for a replacement vehicle since this is definately a defective car.

    During this last visit to the dealer they provided me with a loaner 400H with 25,000 miles and it did not have the smell. I would prefer to stay with the hybrid engine if it is just my car that is the lemon. But, it sounds like they do not have all the bugs out of the hybrid engine yet.
  • wwestwwest Member Posts: 10,706
    There is an aftermarket modification available that you might want to show to your dealer. See and their EED, Electronic evaporator dryer.

    And by the way unless you're really diligent about turning the A/C off it normally operates all the time.
  • ke2feke2fe Member Posts: 37
    An ISC procedure was mentioned to update the software in the 400H. What is this procedure and what does ISC stand for?


  • dibdocdibdoc Member Posts: 1
    We had this happened twice. The first time the vehicle would not start after it occurred and had to be towed in, when they examined it they could not find any problem. It re occurred a few days after we got it back, but it went out after the car turned on that time. We have also had two defective stereo systems, a faulty rear hatch door and are getting frustrated
  • dadcatdadcat Member Posts: 29
    ISC stands for Idle Speed Control. The details of the procedure are in the TSB at the following link:
  • drgkjedrgkje Member Posts: 21
    I feel (just a feeling) that my 400H's engine runs too frequently and the gas mileage is only about 23 but don't have any gear chattering. The car was at dealer's lot for a couple months before deliver, won't be surprised if they jumped it but did not do an ISC. Do you know what the correct idle speed should be or any way to find it out?
  • drgkjedrgkje Member Posts: 21
    P.S. the gas mileage at 23 is a fact
  • ke2feke2fe Member Posts: 37
    How is the message saying "maintainence required soon" or "maintainence due" reset or turned off? I do my own maintainence. (Oil, filter, brakes, etc)
  • nighnigh Member Posts: 16
    I have a 400h with 21000 Miles on it and have never had a single problem with the "stuttering" mentioned. Very smooth ride. And, as far as the dealer cost for an oil change, the Annapolis Lexus dealer will even pick up your car from your home or office and bring it back to you. My husband and I just call and make an appointment for service and reserve a loaner (free) and go about our business. They call us on our cell phone when they are finished. We have free car washes for life, and they always wash it when serviced. They are always friendly and punctual. We have no problems with them... :)
  • sakumarsakumar Member Posts: 1
    I know about Lexus Personalized settings, but having recently bought an RX 400h I noticed on Page 44 of the manual that the Automatic Door Locking/Unlocking functions are user settable.

    But after trying the procedure (ignition ON, move gear lever to "N", within 10 seconds hold down door lock for 5 seconds) I wasn't able to change it to "lock on vehicle speed".

    Anyone else tried this and is there a special trick to getting it to work?

  • PF_FlyerPF_Flyer Pennsylvania Furnace, PAMember Posts: 9,372
    No doubt you've noticed new discussions popping up all over the forums. What's happening is that we are closing large, generic discussions like this one and creating smaller dicussions that focus on different aspects or issues concerning the vehicle.

    For example, here in the Lexus RX 400h Group youwill now find:

    Lexus RX 400h Test Drive - What Did You Think?
    New Lexus RX 400h Owners - Give Us Your Report
    New Lexus RX 400h Engine Problems
    RX 400h Navigation/Bluetooth Issues
    Changes You'd Like To See in the Lexus RX 400h
    Lexus RX 400h Brake Issues
    Lexus RX 400h: Driving Tips & Tricks
    Lexus RX 400h Transmission Questions
    Lexus RX 400h Tire/Wheel Questions
    Lexus RX 400h Suspension/Steering Issues
    Lexus RX 400h: MPG-Real World Numbers

    to mention a few of the new discussions.

    When you are ready to post, please check the dicussion list here at the main Lexus RX 400h Group page to find the appropriate discussion to post in. Should you have an issue or question that doesn't seem to fit an existing discussion, please feel free to start up a new one.

    Thanks for your understanding and help in making this group a great source of info!
This discussion has been closed.