Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Lexus RX 400h Electrical/Lighting Questions

PF_FlyerPF_Flyer Pennsylvania Furnace, PAPosts: 5,854
edited April 18 in Lexus
Discuss electrical and lighting issues here.

Need help navigating? - or send a private message by clicking on my name.
Share your vehicle reviews



  • Lexus is currently installing a "security" kit to discourage theft of the HID lights. It involves installing dots, and a security bracket. It is free, but the kits are backordered so you need to make an appointment. Mine is currently for a week from now. They highly recommend it; especially if you park in the city. They even had problems with the lights stolen from their loaners.
  • krellukrellu Posts: 31
    I just spoke to a service advisor at lexus and he said that this kit is already installed in the 400h.Also said it is in stock for the rx330,in case anybody is interested.
  • It may be installed on the newer 400h, but not on mine. Mine was built in May.
  • krellukrellu Posts: 31
    Mine was built in march.
  • krellukrellu Posts: 31
    I just spoke to someone at customer service at lexus headquarters in Ca.
    800-255-3987.They said no rx400h had these kits installed.First they are working on the rx330 and then possibly the rx 400h.
  • I know that I have to drive to Queens soon and park the car. I don't want my 400h damaged so rather than waiting for Lexus to contact me, I called my dealer who is wonderful and they set up the appointment. They understood the problem because even their loaners have had the headlights stolen when parked in the city. I've decided that the slowest answers seem to come from the Lexus headquarters!
    I originally heard about the kit on another Lexus owners site so I just thought I'd share the info because nobody wants their car damaged or the headache or expense. In the suburbs we're relatively safe, but as soon as the car gets parked in a big city we're sitting ducks. I guess I was just fortunate the car was in a garage most of the time in Philly and lucky when it was parked on the streets for a relatively short time. I'm not planning to tempt fate too long!
  • Got my new 400h on Friday in the UK and it's great - except that, while sitting in the car transferring my phonebook, loading CD's and playing with the ICE video system for an hour or two - the auxiliary battery went flat and wouldn't start the car.

    Rescue truck driver said its because it has a very small auxiliary battery for the size & complexity of the car.

    When I finally jump started it the engine ran for a few seconds and then cut out because the traction batteries were presumably OK.

    Seems weird that the car can be immobile because of a low aux battery when there's all that juice sitting in the traction batteries.

    Anybody know why the design doesn't allow for starting the engine from the main batteries via a voltage converter?

    Anybody else had aux battery problems?
  • wwestwwest Posts: 10,706
    It is my understanding that the 12 volt battery is (re)charged via a DC-DC down-converter from the ~270 volt hybrid battery. Since the down-converter replaces the more typical engine driven ~90-120 amp alternator it should at least have an equal level of capacity.

    So I would agree, it seems really odd that the down-converter, presumably rated at 50 amps minimum, wouldn't supply enough 12 volt "juice" to support the electronic needed to "signal" a need for an engine start.

    Actually what seems even more odd is that the 12 volt battery wasn't being continuously charged via the down-converter as you sat there "twiddling". No reason for that not to work even in the accessory position.

    Also makes me wonder if instead of calling for a "tow" you had simply placed the system in "run" for ten or fifteen minutes to let the downconverter recharge the 12 volt battery.
  • OK - I've taken some measurements and I think I understand what's happening.

    When your sitting in the car "twiddling" with the ignition in the "accessory" or "on" position you can easily discharge the small battery quickly because there is no charging taking place.

    After you turn the key to "start" and the car enters "ready" mode there is a steady 2 - 3 amp trickle charge into the aux battery regardless of whether the engine starts or not. (When the engine starts I guess this goes up to conventional 50A or whatever charging rate but I haven't checked that yet.)

    You're probably right about waiting instead of calling the tow truck - but it would take a few hours at 3 Amps.

    Bottom line is - when twiddling stick to "ready" mode (but not in a closed garage in case the engine decides to fire up!).

    Does anybody know if there's a more technical user or workshop manual available for these cars - no one here seems to understand exactly how they work - including the dealers!
  • wwestwwest Posts: 10,706
    Yes, I bought the Toyota shop manuals for my 03 Prius right after buying it, fairly pricey though.

    There is also a Toyota internet site where the same info is available on a subscription basis.
  • lexi4lexi4 Posts: 8
    1st away for a week. Won't start. jump. ok. sat overnight week later won't start. dealer replaces aux. battery. 2 weeks later. sat overnight won't start. dealer replaces aux. battey. They have no idea.

    Does anyone have an idea / fix for this? no other gremlins. Can we use a larger battery?

  • engnrngengnrng Posts: 4
    Just joined the forum, as we are looking to buy a 400h, already own a Prius (2 years). Assuming 400h electrical system is wired same as the Prius, high voltage batteries are isolated from 12v system except when car is on. This is a critical safety feature for several reasons. The 12v battery is small because all it needs to do is boot the computers that control the ice and high voltage systems. When you turn the key to start, all you are doing is booting the computers. If your battery had enough juice to boot the computers, then leaving it in the ready state would charge the aux battery. Whenever I am fiddling with stuff on my Prius, like the nav system, I leave it on in the ready state. Every few minutes the ICE comes on for a few seconds to recharge the main batteries.
  • Hi,
    could anyone send me photos of the high voltage harness (Batterycable, U-V-W cables of generator / Motor..) and HV connectors of a lexus hybrid?
    Would be very great if you could help me!!


  • I read your comment about the stolen HID lights. My friend's were taken twice in 6 months from his RX330. The dealer said there isn't anything to do, but you seem to have found a solution. I would appreciated your giving me any helpful ideas. I don't know how to get back to this forum since I've never used it. I found your reply through a search. Either please email me at or tell me how to find your answer here. Thanks!
  • I have had several episodes of battery failure recently. For my previous Lexus vehicles, and now my hybrid, I listen to the radio while using the accessory mode - and have never had a problem. In fact, even my daughter has used the Entertainment/DVD system for almost 20 minutes while the car was in accessory mode - and no problems. However, just this week we had problems with the battery. Three times the battery failed. Has anyone had such battery drainage when in Accessory mode operation. We are seeing this problem, during the bitter cold weather. Is the weather a problem? Thanks for your comments. Also, we have seen a drop in mileage. During the summer and fall, we had around 27-28 mpg. Now it is 20. Is anyone experiencing this?
  • PF_FlyerPF_Flyer Pennsylvania Furnace, PAPosts: 5,854
    The extreme cold by itself reduces your battery's starting capacity. Add in the drain of extended use of Accessory mode, and you may wind up with a no start situation.

    Mileage for all vehicles drops during the winter months for a collection of reasons. People tend to warm up their cars, fuel formulations change, slippery road conditions... it all chops away at your mileage in the winter.

    Need help navigating? - or send a private message by clicking on my name.
    Share your vehicle reviews

  • I have to confess that I haven't looked at this forum in a long time. I'm not sure what you're referring to. I had the Data Dots installed on my headlights (they put stronger brackets in, too) back when I wrote about it. They also put many stickers around the car. I've had no problems even in parking lots in Newark, NJ. I understand that the newer 400hs come in with them installed already, however, I don't know if the stickers are visible.
    Unrelated, you can purchase datadots from, too, but it isn't the same as the Lexus installation.
  • krellukrellu Posts: 31
    Have a grill guard installed.
  • Thanks for the insight on the battery. Again on the mileage question - is 19-22 a normal range for the winter? I used to get 27-29 easily during the past year. No matter how I cautious/concientious of a driver I am, just cannot get over 22.
  • supcommsupcomm Posts: 4
    The battery indicator show only 6 bars out of the 8 total as being charged. No matter how long I drive, I cant get the last 2 bars to show charged. Anyone know why this is or has this problem? Should I take it back to the dealer? Thanks.
This discussion has been closed.