c17boom

can I bypass the brake lamp failure sensor on my 1999 rx300??

salimshah

Lot easier to fix the problem, if you describe it a bit.

Like the failure lamp turns ON the first time you apply the brakes. or ON all the time.

Culprits are one of the three tail brake light bulbs.
Brake Fluid level.
Brake switch.
Float in the master-cylinder.

Once the problem is isolated, you can make the best choice for yourself.

Salim

carguy07

I think he is talking about the light that tells you that a brake light or tail light is out. It is super sensitive and can false even if all the bulbs are working. Mine was coming on intermittently for a while. Then a bulb finally went out. Once I replaced that bulb it has stayed off.

c17boom

All brake lights went out at once, no idiot light on dash, all bulbs are fine, have not checked the master cylinder yet, mechanic changed the brake light switch, sensor was next in line he said, part is big money, heard online other people bypassing the sensor and it works fine, thought I would ask the pros before attempting
Thanks

carguy07

So you have no brake lights and no warning light lit on the dash? Master cylinder would have nothing to do with this. There is a little box that controls the light that tells you when a bulb is out, but I have never heard that this can make the brake lights stop working, just throws the warning light on the dash. Sounds more like a short somewhere to me.

salimshah

Still some more questions ...

Is any fuse that keeps popping? Have you confirmed all are good (specially the brake light circuit?
Do you have any trailer hitch electrical connection? Is there rust on it?
Do you recall what caused the brakes lights to malfunction?
How about tail lights, do they turn on when you have the lights on (best way is to check when it is dark)
Lastly do all the instrument panel warning lamps turn on when you move the ignition key from acc -> on/run ... please check the owner's manual to see what should turn on.

Kind of pointless to state that driving with brake lights off is not safe and not legal ... I know you are trying to fix them, but just wanted to list here.

Salim

c17boom

OK, My master Mechanic narrowed it down to this part, He is the best I have worked with around here (Charleston SC). Lexus dealer wants 363$$ for the small plastic box that is stored in the left side cargo area, I pulled the part out yesterday morning went to all parts houses in my area, they looked at the item like it came from Mars.. Next stop salvage yards, these are gold mines for Lexus owners,, Bottom line found 1 rx300 in tri county area and it had the hidden Brake light failure sensor part # 8937320240 took a chance on it being in good working order. IT works perfectly, with a little bit of asking the right question and 25.00 I am glad to say the little sensor is at home on the road again.. and yes when this little box guits you brake lights will not work. oh and they are on every Lexus model I found in the home for 2nd chance parts. I am on the look out for a spare from another 2nd chance parts house.. Thanks for your very valuable help on this very mind bending problem..
c17boom

salimshah

Glad it worked out for you and your baby is back in good health without any compromise.

Salim

carguy07

I found that this box existed when I was trying to chase down why mine was falsing that a light was out. I figured I would just pull the bulb in the dash if it did not stop. This the first time I have heard that the box can kill the tail lights. If you get a chance pop your old one open and see what's in there. I vaguely remember someone saying that it was just some solid state parts like resisters that could be replaced.

c17boom

I did open the sensor up, and it looks like a memory board for adding memory to a computer..
Thanks
c17boom

salimshah

There is a hitch adapter box [logic to mix turn signal to on-of brake light of trailer] and current sensor box for brake light. Current sensing circuit has to be built in series with the load (brake-light), so it is not surprising that you get an OPEN. Normally, one would think the fuse would blow first. We have not seen many members post such a problem. It is new learning for me.

Salim

bwilhite

Hey guys, I've had my tail light failure indicator on for about a month now. It illuminates when I press the brake pedal, so I read the manual and focused on those bulbs. Replaced all of the bulbs (including the high mount), checked the connectors to make sure they were clean, and applied dielectric grease. They all work, but the indicator is still on. Found this thread while doing some trolling, and wondering if it's the failure sensor that's the issue. Where's that box located? If it's not an easy fix, I'm happy to remove the bulb from the indicator or crash the car into a telephone pole because I'm tired of looking at the !#$% light....whichever's easier.

salimshah

Did you replace the bulbs with the proper rating?

Do you have a trailer hitch electrical connector. If there is moisture/corrosion in there, it can trip the sensing circuit.

Salim

bwilhite

Thanks for the reply. There's no trailer hitch on the car and I replaced the burnt bulbs with sylvania's from Autozone. They were the correct part number and had the correct number of filaments in each bulb. The high mount was burnt out, along with right brake light on the rear quarter panel. One of the filaments was burnt out of the bulb in the hatch if I remember correctly, as well. Funny thing is, I think the high mount had been out for a while before the indicator came on. Either way, the bulbs are all new and the light's still on. My first choice is to fix the problem instead of bypass the sensor, but I can't think of what else it could be. Do you know where the sensor box is located, or would it just be easier to pull the indicator bulb? Thanks!

salimshah

I would still try to go for the fix.
Please check the wattage of each bulb and make sure they match with what RX has been speced for. Sometimes the bulb are physically the same but not the right wattage.

Have some one stand behind (preferably right after dusk) and apply the brake. Confirm all 3 are lit up and see if left and right have the same intensity.

Also check if the master cylinder has fluid above the min level.

I am running out of ideas ... maybe some one can suggest some other things to look for.

Salim