Sep 12, 2012 // Other Mods //
Lamp Sensor Fix
(4) rear brake lights do not work, except for the LED brake light on the
(4) rear taillights (same bulbs, different filaments) work OK
are OK and the filaments for the brake lights in the bulbs are OK
probably, the Toyota Lamp Failure Sensor (LFS) has malfunctioned.
LFS (P/N 89373-14080) is in the brake lamp circuit for the (4) rear lamps.
It is NOT in the circuit for the LED lamp which explains why the LED lamp
continues to work. Its purpose is to sense when a lamp filament has burned
out and notify the driver by a warning lamp on the instrument panel.
there is no sensor to detect when the LFS itself malfunctions, and the
driver is simply left without brake lamps (except for the LED)
(at least 4 known cases) the LFS has malfunctioned simply due to a cold
solder joint, or a cracked trace on its printed circuit board. These can
be easily repaired and will save the owner a bundle. (Most Toyota dealers
charge over $225 for the LFS part alone.)
LFS is in a small light blue plastic case (about 2 x 2 x 1) and
is located in the left rear quarter panel of the Supra, in the well behind
the wheel. Its easily accessible by removing two plastic covers in the
Phillips head screwdriver
wattage (<25 watts) soldering iron
Required to Fix:
about 20-30 minutes
your soldering iron plugged in so itll be ready the rest of this
will only take about 10 minutes
the rear hatch and peel back the carpeting on the left rear side (see
out the black plastic plugs covering the fasteners for the left side
plastic panel, and the small triangular panel covering the left rear shock
the 5-6 phillips head screws for the side panel, and the shock tower
the (2) Toyota black plastic rivets one is on the shock tower panel,
and the other is holding the left side panel to the rear panel (covering
the taillamp). Look closely for it, its there, but its buried!
the shock tower panel off, and the left panel out careful with the
left panel be sure to disconnect the interior lamp from its harness,
and if you didnt find that 2nd plastic rivet the panel is
not coming out!
the light blue plastic tab protrudng through the sheetmetal. It will
probably have the hatch release cable and another harness running right on
top of it. This is the LFS.
into the well opening and hold the LFS with your left hand, and push on
the blue tab with your right it should pop right out.
the LFS from the well, and remove the plastic harness connector.
it over and see how the back fits on remove the back to expose the
printed circuit board.
you look carefully at all the traces, you may be able to see a crack or a
cold joint. Several list members who have had this problem reported
finding the fault this way. With your soldering iron carefully try to
bridge the crack with the existing solder on the board (theres plenty),
or touch up the cold joint. Try not to add new solder as it may bridge
traces where its not supposed to!
my eyes were too old, or my LFS simply had a cold joint which I couldnt
detect. After staring at this board under a magnifying glass for 10
minutes, I took the easy way out and touched up every solder joint.
reassemble just yet, but reconnect the LFS to its harness and see if you
have brake lights now. If you do congratulations! Youve saved
yourself at least $300-400 in dealer service charges.
you dont have brake lights yet, and you didnt resolder every joint
on the board (as I did) try this approach now, maybe you have more
than one fault. Try not to add any new solder!! On my LFS I noted there
was plenty of solder and I had to be careful that the excess didnt
bridge adjacent traces.
youve had success reassemble everything! If no success, reach deep
into your pocket for that $237 for the Toyota dealer. (If its any
consolation, Jeff Watson at Jay Marks will sell it to you for $150)