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PostPosted: January 12, 2018, 11:56 am 
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Joined: October 10, 2010, 10:26 am
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Location: Bakersfield, CA
I'm having an odd issue with my aftermarket LED check engine light flickering when not truly lit (on)..

I'm running a late model (2009 Ecotec 2.0) GM turbo engine/ECM, and the stock in-dash CEL calls for an "L37" standard bulb.. in my case, since I'm not running the donor car's dash, I've just wired in a small LED bulb as my CEL, but it does this odd flicker thing I'd like to resolve..

What is known: The ground to the bulb is good / The LED CEL comes on solid when it should (when I throw a code it lights up super bright and stays on solid red)-it seems to be functioning perfectly for it's purpose / The "flicker/pulse" is very dim- it's actually hard to see unless you're looking for it (this flicker is NOT the CEL trying to flash as if there's a problem... this flicker is almost like ghost voltage :leave: ) / The flicker is very steady at about 6 or 7 pulses a second, and it does not matter what the engine rpms are, it stays steady / battery-alternator-charging system seem to be working perfectly-battery lugs are tight / the LED CEL bulb will not flicker until I start the car (does not flicker with key 'on' or 'acc' without the motor running)... also for what it's worth, I'm running the same type/size LED as my car's 'charging idiot light,' and I'm not getting this odd flicker through it..

So it seems I've wired in an LED where a standard bulb wants to be; surely I can't be the first person to get this odd flicker.. My guess is I need to trick the LED into proper function with an inline resistor(?) or dummy load(?).. what I don't understand about electrical theory could fill a library, so I'm obviously out of my depth .. I've Googled a bit on this, and keep tripping up on the proper functioning/flashing of a CEL, not the errant malfunctioning of an LED..

Any thoughts on how to make this LED stop this annoying behavior?

thanks-

--ccrunner

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PostPosted: January 12, 2018, 12:39 pm 
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Joined: June 15, 2010, 8:29 am
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Location: Duxbury, MA USA
OBD2 checks to make sure the "check engine light" bulb is good. This is probably where the power is coming from. Should not be hard to work up a circuit to run most of the voltage around the LED. You want to keep the voltage on the LED below its forward voltage when you want it off. You need low enough resistance in the circuit to keep the ECU from throwing a fault code for a blown or missing bulb.

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PostPosted: January 12, 2018, 12:41 pm 
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The first thing that I would suggest is try adding a 1N4001 diode (or some other general purpose 25V or more diode. Even a 1N4148 should work.) in series with the LED and see what happens. It will require another 0.7V before the LED starts to light up. Low voltage spikes will have a tougher time activating the LED.

If this doesn't work, an LC should work too. But I think the diode fix will work.

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PostPosted: January 12, 2018, 12:47 pm 
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Series diode was my first thought too. I dont know what his inspection situation is, but if they dont check OBD2 port that will work almost for sure. If they do check, it will fail for missing check engine light bulb.

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PostPosted: January 12, 2018, 1:00 pm 
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So what happens if the CEL bulb is out? How will it notify you the bulb is out? Inquiring minds want to know. :roll:

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PostPosted: January 12, 2018, 2:15 pm 
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Location: Bakersfield, CA
rx7locost wrote:
The first thing that I would suggest is try adding a 1N4001 diode (or some other general purpose 25V or more diode. Even a 1N4148 should work.) in series with the LED and see what happens. It will require another 0.7V before the LED starts to light up. Low voltage spikes will have a tougher time activating the LED.

If this doesn't work, an LC should work too. But I think the diode fix will work.

Thanks for the replies guys.. I didn't think to include that this car (1963 Volvo 1800S) is California smog except as it's older than 1975 -no smog checks on this car ever.. I just need the CEL to work properly to alert me to trouble, and stop winking at me when there's no issue.. I can try the suggestion "...adding a 1N4001 diode (or some other general purpose 25V or more diode. Even a 1N4148 should work..." for sure, but if that doesn't kill the flicker, Rx7, what is an "LC?"

**also, remembering that I don't know doo doo about the black magic of electricity :roll: , the 1N4001 goes inline on the positive lead to the LED(?), with the cathode end toward the LED(?)

--ccrunner

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My '72 Honda N600 build log (bike engine in a microcar)...
viewtopic.php?f=36&t=14452

My '63 Volvo 1800 with a turbo inline 4 build log (LNF Ecotec compliments a Svelte Swede)
http://locostusa.com/forums/viewtopic.php?f=36&t=16309


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PostPosted: January 12, 2018, 2:40 pm 
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I'd try a 1K resistor and a .1uf cap in parallel with the LED.

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PostPosted: January 12, 2018, 3:24 pm 
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rx7locost wrote:
So what happens if the CEL bulb is out? How will it notify you the bulb is out? Inquiring minds want to know. :roll:

If you interrogate the OBD2 port the code shows up. Is really only an inspection thing, but it will cause a "fail" if your state (like where I live) requires that it be working.

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PostPosted: January 12, 2018, 4:10 pm 
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ccrunner wrote:
rx7locost wrote:
The first thing that I would suggest is try adding a 1N4001 diode (or some other general purpose 25V or more diode. Even a 1N4148 should work.) in series with the LED and see what happens. It will require another 0.7V before the LED starts to light up. Low voltage spikes will have a tougher time activating the LED.

If this doesn't work, an LC should work too. But I think the diode fix will work.

Thanks for the replies guys.. I didn't think to include that this car (1963 Volvo 1800S) is California smog except as it's older than 1975 -no smog checks on this car ever.. I just need the CEL to work properly to alert me to trouble, and stop winking at me when there's no issue.. I can try the suggestion "...adding a 1N4001 diode (or some other general purpose 25V or more diode. Even a 1N4148 should work..." for sure, but if that doesn't kill the flicker, Rx7, what is an "LC?"

**also, remembering that I don't know doo doo about the black magic of electricity :roll: , the 1N4001 goes inline on the positive lead to the LED(?), with the cathode end toward the LED(?)

--ccrunner




Yes, the diode goes in the Positive lead with the cathode end (band) toward the LED. You can't do it wrong and hurt anything. If you have the diode in backwards. If it is in backwards, the CEL will not work at all, even when it should. Just reverse the diode.

If that improves, but doesn't fix it, you could try 2 diodes in series.

LC is inductor (L) and Capacitor (C).

300D50's answer might work but will reduce the brightness of the LED, possibly noticeably. An LED requires a current limiting resistor which may be within the LED housing. It may be a separate resistor. Depending on the LED style you have, you might be able to add a cap simply across the actual LED and use its current limiting resistor as 300D50's 1K resistor. We can go there if necessary.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

My RX7 powered Locost is now for sale http://www.locostusa.com/forums/viewtopic.php?f=40&t=18460

or visit my Cushman Truckster resurrection log: over HERE


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