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997.2 LED reverse light bulb upgrade - I thought I had it figured out!

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997.2 LED reverse light bulb upgrade - I thought I had it figured out!

 
Old 04-01-2019, 02:16 PM
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gsxrjjordan
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Default 997.2 LED reverse light bulb upgrade - I thought I had it figured out!

Hey all - did some searching yesterday and can't seem to find anyone that figured this out, but I'm hoping the collective group here can!

I feel like the incandescent bulbs ruin the 'modern' look of my Cararra White 997.2 TTS, so I've been on a mission to replace them with white LED's. These've been out 9yrs, surely everyone's figured this out?
I get to the reverse lights and had seen them listed as 1156's, but lo and behold, they're Phillips PH16W modules (bulb itself is not removable from the module)


... and you've got to do a little work to get in there. Protip - use a few dabs of RTV silicone to hold the rubber seal in place in the tail light housing when you reassemble the tail light cover.




So I ordered some "CANBUS error-free" LED replacement modules (come with a very good looking light and a ~40ohm resistor pack) from Amazon - apparently E9x BMW's and Audi A8's use the same module in their reverse lights.


Installed the first one and tested, worked perfectly! No errors and beautiful, bright reverse light (new one on the left)


... installed the second one, and got a "Check Reversing Lights" message on the dash, and reverse lights illuminate for a second or so, then die out.
Swap a single incandescent to the left and a new LED to the right, works great. Install the second LED, error (so not the new module, or the tail light).
Both LEDs test fine on the bench, both resistor packs are right under 40ohms.

Phillips incandescent module is typical ~1.2ohm resistance
The Phillips incandescent module pulls about 1.2A, whereas the LED modules themselves pull about 200mA without the resistor pack, and 500mA with the pack. I wired in a potentiometer in series with the resistor pack and was able to get just under 1A current draw, but still got the error.

Question is two parts I guess:
1) Does anyone have LED reverse light bulbs that work for 997.2?
(without errors)
2) If not, does anyone know from any Porsche documentation what the light control module is testing for when it errors out? I'm happy to make a conversion module if I knew what I was designing for, but without knowing what it's seeing, it's a shot in the dark.
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Old 04-01-2019, 02:51 PM
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Sounds like you know what you're doing. I got a little lost on what you tried (and didn't read that closely), did you test the resistance of the incandescents while they were illuminated?
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Old 04-01-2019, 03:45 PM
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Sounds to me like you just need to figure out the resistance of the two original bulbs, then subtract the resistance of the new LEDs and the install a resistor in the circuit that tricks the computer into thinking the original incandescents are still back there.

If the replacement of one of the old bulbs doesn't trip the warning message, then it sounds to me like there's quite a bit of wiggle room to get the resistance right and make it work.
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Old 04-01-2019, 03:55 PM
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?watching this one.
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Old 04-01-2019, 04:12 PM
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I can personally tell you that these work. I purchased and installed them in my 997.2. NO errors, NO issues.

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
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Old 04-01-2019, 11:06 PM
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These are the days you wish radio shack was still in business. I think you are on the right track, but just need a larger resistor pack.
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Old 04-02-2019, 03:59 AM
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Thanks guys - I don't think this is a resistance measurement issue - usually that's blinkers, and a flasher relay that need a resistor along with a cap to set flash speed. I haven't done any OEM work on light control modules/etc, but I believe they're using current measurement to detect a short or open circuit.
The LED uses a driver circuit and the resistor pack not to match the resistance of the incandescent bulb, but its current draw. As you add resistance, voltage goes down, and I'd imagine the LED driver is using a DC-DC converter to keep forward voltage on the LEDs constant, but without knowing how it's set up I can't "guess" a resistor value that'd hit a target current draw.

Originally Posted by SweetWater View Post
I can personally tell you that these work. I purchased and installed them in my 997.2. NO errors, NO issues.

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
Interesting! That company is actually in San Diego near me, I'll stop by tomorrow. Thanks for posting! This might be easier than I thought haha.
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Old 04-02-2019, 08:46 AM
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Originally Posted by gsxrjjordan View Post
Thanks guys - I don't think this is a resistance measurement issue - usually that's blinkers, and a flasher relay that need a resistor along with a cap to set flash speed. I haven't done any OEM work on light control modules/etc, but I believe they're using current measurement to detect a short or open circuit.
The LED uses a driver circuit and the resistor pack not to match the resistance of the incandescent bulb, but its current draw. As you add resistance, voltage goes down, and I'd imagine the LED driver is using a DC-DC converter to keep forward voltage on the LEDs constant, but without knowing how it's set up I can't "guess" a resistor value that'd hit a target current draw.



Interesting! That company is actually in San Diego near me, I'll stop by tomorrow. Thanks for posting! This might be easier than I thought haha.
Whatís wrong with the lights he suggested? Why donít you just use those??
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Old 04-02-2019, 09:34 AM
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I am having similar problems trying to get some LED reversing lights for my 957 and I have tried quite a few with no success. As already mentioned, I don't think it is purely a resistance issue because I have tried several combinations. There is one (slightly weird ) option though - connect a relay in parallel with the original lamp circuit (with original filament bulb tucked away somewhere) and have THAT switch an LED. It kinda defeats the object of the conversion but at least you have a wide choice of LEDs to choose from

I have just ordered some 'Canbus compatable' LEDs from Aliexpress so I will keep you posted
https://ae01.alicdn.com/kf/HTB1Cj4ia...anBus-1156.jpg

Last edited by RazMan; 04-02-2019 at 09:56 AM.
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Old 04-02-2019, 02:15 PM
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Originally Posted by gsxrjjordan View Post
Thanks guys - I don't think this is a resistance measurement issue - usually that's blinkers, and a flasher relay that need a resistor along with a cap to set flash speed. I haven't done any OEM work on light control modules/etc, but I believe they're using current measurement to detect a short or open circuit.
The LED uses a driver circuit and the resistor pack not to match the resistance of the incandescent bulb, but its current draw. As you add resistance, voltage goes down, and I'd imagine the LED driver is using a DC-DC converter to keep forward voltage on the LEDs constant, but without knowing how it's set up I can't "guess" a resistor value that'd hit a target current draw.



Interesting! That company is actually in San Diego near me, I'll stop by tomorrow. Thanks for posting! This might be easier than I thought haha.
If you can take the housings apart, then that's as hard as the install gets. The holes for mounting are not 100% lined up with ours, but a washer on both sides takes care of the space. Mine are installed and fit tightly.
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Old 04-02-2019, 02:49 PM
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LED's already look dated as the new cars all have the LED "neon" look now .... Why bother ...If they aren't broke leave em alone .. more headache that it's worth...
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Old 04-02-2019, 05:31 PM
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Suncoast has them. Have installed on both of 911s Iíve owned and no issues.
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Old 04-02-2019, 06:27 PM
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Did you flip the led bulb around? Iím sure you already know that they only work one way.
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Old 04-10-2019, 04:13 PM
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Sorry for the delay in updating, neither the newborn or my toddler are interested in letting me on the computer haha.

rileyracing1 I disagree I guess. I agree that not all LEDs look the same, and that newer cars tend to have 'bluer' white LEDs, but I felt like the incandescent reverse lights contrasted with the Carrera White paint to make me want to follow through on this.
Another comparison shot between the factory incandescent:


... and the LED with the same 'manual' settings on my Pixel


jkw911 I did reverse polarity - LEDs by themselves are obviously polarized, however the modules (with driver circuitry) are not. They work equally well (same current draw) regardless of input polarity.

It turned out that the ones SweetWater suggested, sold locally here in San Diego by DDM Tuning, worked. Thanks for the tip! DDM load resistor measured out at ~24ohms, for reference.

Here's all three lined up together - sorry for the epoxy floor pic that's hard to look at up close lol. Stock module on the left, my first Amazon purchase on the right, and the DDM LED in the back


The only trouble was that instead of using a 'module' like the stock light, they cheated and soldered some tin hoops to the base PCB - on one side it was just a little tight but screwed in fine, the other was extra tight, and needed the rings 'pinched' to screw in straight


Comparing the original Amazon LED on the passenger side and the new DDM Tuning LED on the driver's side - very similar, but not identical. I don't have a preference between them - but no errors with this combo...


... so I finished by installing the other DDM LED module on the pass side. Pic was before I screwed the tail lights back in the fenders.


Mark this one solved! Thanks boys!
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Old 04-10-2019, 05:35 PM
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Awesome!
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