G_ride

iTrader: (1)

My car has the tail light failure warning light on my dash. I heard that you could pull the bulb from the dash to get rid of the tail light failure warning. Has anyone here done that? And if so please, explain how you did it? Thanks. By the way I have the LED tail lights which causes the tail light failure warning. I already tried 3 sets of resistors even called the dealer to see if they could somehow turn it off, but no luck.

randal

The warning light circuitry works by detecting the current draw of the tail lights. Since you are now pulling less current, the circuit "thinks" the bulbs are burned out. But you already know this. So, couple of questions: How do you have the resistors connected? (across "parallel) with the existing LED, I presume). Then, what value are the resistors? I am not sure of the trip level of the current sensor but would guess you would need a resistance of no greater than 24 ohms across each tail light connector.

socal3

iTrader: (2)

I hope this tread stays alive cause I have the same problem. I just bought my LS so I will check in on mine soon.

StanVanDam

On the 2002, each rear tail cluster has a total of 6 bulbs:
1 x 21W backup light
2 x 5W tails
1 x 21W stop light/rear fog light
1 x 5W tail light
1 x 21W rear turn signal light

Watts = Volts * Amps
Watts = (Volts squared)/Resistance = (Amps squared)*Resistance

Assuming the operating voltage is 12 volts:

5 Watts = 12 Volts * X, solving for X = .416 Amps
5 Watts = 144 / R, solving for R = 28.8 Ohms

21 Watts = 12 Volts * Y, solving for Y = 1.75 Amps
21 Watts = 144 / R, solving for R = 6.857 Ohms

You'll need to figure out:
* Which bulbs are replaced by LEDs (ie. if every standard bulb is replaced by exactly 1 LED, this makes it easy).
* How the lighting ECU calculates the tail light failure (ie. by total current draw across both clusters or by individual clusters, or by current draw from individual bulbs, or by resistance across individual bulbs, etc). Resistance across a burned out bulb would be read as excessive or infinite, with no current draw.
* How the bulbs are wired to the lighting ECU (series or parallel or maybe even both). This affects how you add up the above numbers.

Determine the current draw of the LEDs via the spec sheets or by connecting an ammeter in series, and then you'll know what the amperage difference is from standard.

You can then determine the required resistance using the formula Resistance = Volts/Amps.

randal

I seem to recall seeing the circuit that Lexus uses for this application although it was probably for an LS400. IIRC, they use hi-side current sense with an op-amp comparator. One sensor per tail light side. And I believe the comparator tripped somewhere just north of the 2/3 full current mark.

Now, given that there are 3 tail light bulbs @ 416 ma each, you would need to pull 1.25 amp to simulate all bulbs. It makes sense that the sensing circuit would need a little more than 2x416 ma (832 ma) to determine if just one bulb were out. I do not know how much current the LED's draw but you will need to meet this 2/3 current mark minus the LED draw. It would probably suffice to just meet two bulbs worth of current and hope that the LED's push you over the comparators trip threshold. This would, of course, have to be done on each tail light side.

So, 12v/832ma = 14.4 ohms @ 10w. A rather hefty resistor that is going to get warm so placement would be crucial (ie: keep it away for anything you do not want to burn). All in all, it might be simpler to just mount two tail light bulbs on each side in the trunk. A waste of energy either way... but simple.

StanVanDam

Not a bad idea, one could theoretically fashion these extra taillights into additional trunk lights since the standard single trunk light is pretty dim. Solve 2 problems with 1 fix.

socal3

iTrader: (2)

Not a bad idea at all