Lamp Failure Sensor - 1997 Lexus Ls400

[George Z.]

I have a 1997 Lexus LS400. I recently had the "Lamp Failure Sensor" trigger the light that turns on in the dashboard and I found out that it had 1 brake light and both license plate light bulbs burnt out. I changed out all 3 bulbs and I confirmed that there are NO more light bulbs that are not functioning or turning on in the car when examining it in the night-time.

However, every time I turn the car on (which is only in the night-time) and I have the "automatic lights" turned on, as soon as I depress the brake pedal, this Lamp Failure Sensor triggers the light in the dashboard every single time.

Any suggestions as to whether this light keeps returning? Do I need to swap out & change this "Lamp Failure Sensor" which I found it is located in the left side of the trunk compartment. Or is it possible that some of the brake light connections are possibly corroded and sending out this signal to trigger the light to come on in the dashboard (even though all the lights are working properly in the car).

Thanks in advance for your help.

George

[1990LS400]

The problem could also be a bad bulb with a loose filament that hasn't burned out yet, a bad ground, or a bad bulb socket.

I had a similar problem on my previous 90 LS400 for over a year. I finally traced it down to a loose connection on a trailer light wiring harness that had been installed years earlier and which either vibrated or got pulled lose.

I'd suggest changing all the back bulbs first -- especially if it has been over five years since they were changed ... they usually get blackened with age anyway. If that doesn't resolve the problem then look for a corroded ground or bad socket. I think it is fairly rare for the sensor to fail.

I thought it was funny a few years back when another forum user reported a similar problem and I told him about my loose trailer wire harness. It turned out that he also had a loose connection in a trailer wire harness ... odd because so few LS400's are wired for trailer lights.

[billydpowell]

also check the brake light in the back window.

[jcrome04]

The tail lamps are dual filament bulbs...

Have someone check them when the brakes are depressed.

When I got my LS I replaced all the bulbs in the back. Was a little spendy but the lights are a lot brighter, and now I don't need to worry about any burning out!

One of my high mount brake lights must have been installed by a dirty hand.. This is a good example of why to be careful when installing bulbs.

http://us.lexusownersclub.com/forums/index...c=45718&hl=

[fsuguy]

Hey guys,

I need some help with my brakes, I think - here is the problem:

When I first got the '92 (about a year ago), the brake lamps and some of the tail lights were not working; tracked the problem down to a break in the circuit on the light failure sensor. Soldered that, and put a dab of jbweld to keep the circuit on the board (it looked like heat had lifted it off and also melted the circuit connection, which caused the original problem). Anyway, a couple of days back my stop light fuse blew and replacement immediately blew as soon as I stepped on the brake pedal. Went through a whole set of new fuses (25 amp) without any change.

Here's what I did to check:

I disconnected the right brake lamps and checked and fuse blew; disconnected left brake lamps and fuse still blew; disconnected both left and right brake lamp assys, and fuse still blew; disconnected light failure sensor, and fuse does not blow! So, I think the LFS is the problem(?) I checked the LSF but nothing obvious seems to be the problem except for one of the nichrome (i think that is what it is) sensors looks like it is subject to high temps (appears like tarnished silver).

Do you think it may be the LSF causing the fuse to blow, or something else? How can I fix this without springing for a new LSF ($438) for what is essentially a 2X2 circuit board with about 8 resistors ($10.00), 6 capacitors ($10.00), and a couple of otherwise inexpensive components. I need to let the potential rear-enders know I am stopping, and this scares the heck out of me, since I have been rear-ended (totaled a really cool customized Pontiac T/A about 20 yrs ago, with fire and explosions, etc.)

Also, have you seen this type of problem before?

TIA

fsuguy

:P

[George Z.]

I just wanted to follow-up on this thread and let you know that I changed the "3rd-tail lamp" light bulbs (which are bulb #921) and when I put 2 Sylvania bulbs from AutoZone and I started the car and depressed the brake pedal, the light no longer stayed illuminated in the dashboard.

Apparently, the 2 bulbs which were in the 3rd tail lamp brake light were very cheap ones (that were still working, might I add) - but they seemed as if their design had very thin wiring or elements that were sending an inaccurate signal to trigger the light to remain on in the dashboard.

Hope it helps & thanks for all of your replies !!!!

George