Unfortunately, the service manual information is INCORRECT, or at least not clear about what it considers a taillight.

The TAILLAMP FAILURE message also applies to the tiny bulbs in the front headlights. This has been discussed in these forums previously but perhaps not everyone saw the discussion.

You can easily test this by unplugging any of the tiny front headlight bulbs or switching them out for LEDs. You will get a TAILLAMP FAILURE message, when in fact the location of the bulb is in the headlamp, not taillamp.

 

My 01 didn't apply to that rule, I drove for 3 years with 3/4 of those T10 bulbs not working up front. I didn't even know that they were out.

EDIT: It didn't even care when I had LEDs for license plate lights.

 

That's correct. That message will display if a tail light bulb (5 watt bulb) or brake light bulb (dual filament 5-watt / 21 watt bulb) is out (both type bulbs in rear only).

 

In my case, the tail lamp failure warning light did not come on when the small bulbs inside the headlight assembly were out. I only found out that they were burnt out when I went to replace my ballast in both sides. If the failure lamp only lights when your lights come on it should be fairly easy to find the problem. It has to be associated only with the lamps that light when you're lights come on. Remember that the failure lamp will light up if one of the filaments in a dual filament bulbs is out. At least in my case it did. Make sure you find every bulb in the taillights. There are small ones on the side that you really can't see very well inside the access hole. Also check to make sure all of the contacts inside the light socket are in good shape iand have enough spring to make sure all contacts are touching firmly

 

Roman, as I noted in post # 6, suggest you PM Yamae if you intend to bypass/disconnect any ecu. Here's a relevant post from Yamae: https://www.clublexus.com/forums/ls-...cf20-21-a.html

 

As I mentioned, prior Lexus/Toyota models utilized a separate failure detection module, whereas in the LS430, it is integrated into the luggage room JB/ECU.

As Yamae mentions at https://www.clublexus.com/forums/ls-...ml#post9171768, "Toyota has completely changed the design and the one for a LS430 is totally different. The function is included in the other unit called a multiplex rear junction computer."

In that thread, Yamae found a circuit diagram for the LS430 detection circuit. See attached for the correctly-rotated pic.

 

I just have posted another idea which only requires to change the sensing resistors at below.
https://www.clublexus.com/forums/ls-...ml#post9345251

 

Excellent work Yamae and thank you for that info. Now we see that the ECU works by detecting a voltage drop via the current-sensing resistors, which matches the generic Lexus lightbulb failure detection high-level circuit diagram in my post #7.

RomanTPA, let us know if replacing those surface-mounted resistors disables the taillamp failure detection circuit. Here is an example of a 0.4 Ohm 4527-package automotive current-sensing surface-mounted resistor - https://www.digikey.com/product-deta...40CT-ND/713550. Your local electronics shop may have small quantities of resistors for cheaper.

 

Yamae, thanks, as always, for your helpful post.

 

You are welcome, Tom. But it's you guys who confirm that the method for a JDM is also effective for a USDM or not. A Japanese UCF30/31 Celsior is mostly the same with a LS430 but there are some differences. I hope my analysis result is effective for your LS430.

 

I agree that you should replace ALL of the lights in the rear of your vehicle first including the small side lights using non-LED lights whether they appear to be functioning correctly or not~a tiny break in a filament might be the cause of the problem.

The LFCM is located behind the upper panel in the left rear of your RX-300. It takes longer to remove all the panels to get at the LFCM than it does to replace it! Make sure you keep the screws & washers with the parts that you need to remove to gain access to the LFCM! A new LFCM from your Lexus dealer can set you back almost $500!

I watched my mechanic while he temporarily bypassed the brake light failure on the wiring harness that leads into the Light Failure Control Module by using a wire clip to join between the brake control wires PRIOR to their entering the plug that connects into the module. The wires are the second upper & lower in from the left side of the connector with the connector clip facing upwards. The function is still controlled by a blade fuse so it's safe for your vehicle but the function failure idiot light stays on in your dash as long as you leave this temporary fix in place. And, of course, now your brake lights will work.