Clearing Up Misconceptions on the CAN Bus, PWM, and Flickering Headlights - Page 2 - Jeep Wrangler Forum

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Old 01-25-2015, 07:50 AM   #31
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I would love to see what you find. Fascinating stuff. Thanks for the work!
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Old 01-29-2015, 07:12 PM   #32
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I am going to install driving lights on the front bumper, the relay for them is supused to be triggered by the high beams . Can a rellay be operated with the pmw to the headlight?

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Old 02-07-2015, 01:09 PM   #33
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I have a question that may or may not be related to CAN bus. I purchased front and rear Ace bumpers on a Black Friday sale last November. These bumpers have integrated LED light bars, a 20" two row in the front and two 6" single rows in the back. I wired the front into the fog light harness and the rears into the reverse light harness. The LEDs seem to work just fine. But ... now my HVAC goes nuts when I start my car. Nuts, meaning that for several seconds (30 or so) it cycles through various temperature, vent and fan configurations while the rear window defrost light flashes. Related? Maybe not. But it seems like a CAN bus thing.

Thoughts?
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Old 02-07-2015, 01:29 PM   #34
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Quote:
Originally Posted by Fla Tom View Post
I am going to install driving lights on the front bumper, the relay for them is supused to be triggered by the high beams . Can a rellay be operated with the pmw to the headlight?
They can, but generally you'll need a capacitor to even out the voltage flow so that's enough to drive the relay trigger without it going nuts. There's some HOWTOs on how to do that out there. It's pretty easy.
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Old 02-07-2015, 01:31 PM   #35
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Quote:
Originally Posted by terrabit View Post
I have a question that may or may not be related to CAN bus. I purchased front and rear Ace bumpers on a Black Friday sale last November. These bumpers have integrated LED light bars, a 20" two row in the front and two 6" single rows in the back. I wired the front into the fog light harness and the rears into the reverse light harness. The LEDs seem to work just fine. But ... now my HVAC goes nuts when I start my car. Nuts, meaning that for several seconds (30 or so) it cycles through various temperature, vent and fan configurations while the rear window defrost light flashes. Related? Maybe not. But it seems like a CAN bus thing.

Thoughts?
Easiest thing to do is to temporarily disconnect the LEDs just to see if you have a difference in behavior.

Chances are it isn't that, but something else related to the bumpers that is confusing it. Did you perhaps damage the front ambient temperature sensor (mounted on the grill frame)?
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Old 02-07-2015, 02:40 PM   #36
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Quote:
Originally Posted by dcgibbons View Post
Easiest thing to do is to temporarily disconnect the LEDs just to see if you have a difference in behavior. Chances are it isn't that, but something else related to the bumpers that is confusing it. Did you perhaps damage the front ambient temperature sensor (mounted on the grill frame)?
I don't know. Ambient temperature still reads on AVIC. How would I check? Where is this sensor located?
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Old 02-07-2015, 02:51 PM   #37
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Scribed...got the same ACE Bumpers coming!!
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Old 02-07-2015, 03:21 PM   #38
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Quote:
Originally Posted by terrabit View Post
I don't know. Ambient temperature still reads on AVIC. How would I check? Where is this sensor located?
If it still reads in the EVIC you're fine. It's located on the driver's side, behind the front grill, in front of the radiator. You can see it easily without taking the grill off. It looks like the end of an electrical connector with a wire going towards the driver's side headlamp.
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Old 02-08-2015, 01:35 AM   #39
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Quote:
Originally Posted by dcgibbons View Post
If it still reads in the EVIC you're fine. It's located on the driver's side, behind the front grill, in front of the radiator. You can see it easily without taking the grill off. It looks like the end of an electrical connector with a wire going towards the driver's side headlamp.
Thanks!
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Old 02-09-2015, 09:35 AM   #40
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Is there a possible difference between a vehicle destined for the US vs a Canadian vehicle?
I have heard rumors that they system may be set up different? Aside from DRL, I wouldn't see a reason for it to be different.
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Old 03-17-2015, 10:40 AM   #41
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so ok, I bought and installed some LED driving lights and wired them into the switch for the factory driving lights on the turn signal stalk. also put an LED light bar on wired direct. no problems with the light bar, but the LED driving lights flicker on start up and shut down of the engine, but work fine when switched on
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Old 03-17-2015, 11:31 AM   #42
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I'm in Canada. I purchased the procal, reset my DRL's to fogs. Purchased the Trucklite anti-flicker modules, Flea Bay LED's. Only problem I had was that the LED lights I had were H13 plug, Truck lite modules were H4 output.

I snipped the harness of the LED's and installed spade connectors which were then connected to the H4 harness.

Installed, no flicker, nice light.

I also purchased LED headlights with a heat sink only. I didn't like the idea's of fans as a point of failure.
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Old 05-11-2015, 09:48 PM   #43
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I replaced my stock fog lights with Rigid LED cubes. Why would this "system" cause my LEDs to blink randomly while the can has been parked? Is there a simple fix?
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Old 06-04-2015, 02:30 AM   #44
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I replaced my stock fog lights with Rigid LED cubes. Why would this "system" cause my LEDs to blink randomly while the can has been parked? Is there a simple fix?
*exact* same thing happening on my 2015 JKUR. If they were red and blue, you would think it was a cop light.

Any ideas?
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Old 09-28-2015, 09:31 AM   #45
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Question: Would installing a relay to run the headlights directly off of battery power result in brighter lights? Seems my stock lights are pretty dim, hard to see anything when it's raining. Seeing as the battery is 12-13v, and the headlights are running 8v, this sounds like it could be a fast and easy way to increase brightness. Thoughts?

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Old 10-03-2015, 11:51 PM   #46
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Disclaimer: I'm new to jeeps but since my sons new jeep seems to have a TIPM problem, I will be taking a deep dive into this system and the CANbus might become a target of my interest. But for now the relays (and probably the solder joints based on my experience with a 96 GC ECM) seem to be the weak links. But I have not laid hand on any of this jeep yet (its still at the dealer hoping they can find the problem) but I have some experience with the circuits being discussed.

My 2 cents...
The answer to your question is that it depends on the drive signal. Short story made long, it depends how the 8v is measured. If 8v was measured by the peak of the waveform then a straight 13.5 V would certainly shorten lamp life, but if measured with a meter, the signal would be "averaged" by the meter and the reading it displays would depend heavily on the frequency, pulse width and duty cycle of the signal and the capacitance, if any, of the headlamp assembly circuit.

In the ideal system with no capacitance resulting in 8V DC, a 50% duty cycle would mean a 16V voltage supply (not impossible, but pretty unlikely in this case). 75% duty cycle would mean 12V supply and an unmodulated 13.5VDC to the lamps would be fine. Point being we don't know until we see that signal.

I have a lot of trouble accepting that a 1-2% increase in fuel economy is the result of this headlamp modulation, but the author of that post appears to have some credibility so I'll differ to his experience.

I'm also not sure why the PWM is a good option for headlamps. Is it possible that high beams simply use 100% duty cycle?

I also read that replacing with LED lamps cause flicker and adding capacitors into the circuit fixed this. It probably does, but the PWM driver is probably designed to drive an inductive load so the additional capacitance could damage the circuit driver. Seeing how close to component design limits it appears Chrysler designs these assemblies, modifications can possibly cause unexpected behavior.

Just adding to the discussion.
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Old 10-04-2015, 07:05 AM   #47
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Chopper,

Check out this wiring harness from Susquehanna Motor Sports:

HL28130JP H13 to H4 Upgrade Headlamp Harness - Jeep JK Wrangler 2007>

It does exactly what you suggest and I and many others have installed Hella or Cibie H4 lamps in conjunction with this harness.

You can also have them add a wire to use as a trigger to another relay. I'll use that feature to let a pair of driving lights come on with the high beams.

No affiliation; just a satisfied customer of SMS.

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Old 12-10-2015, 11:10 AM   #48
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great information here. thanks for putting in the work for new people like me to find.
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Old 02-27-2016, 12:41 AM   #49
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great write up and very informative. thanks!
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Old 04-03-2016, 08:41 PM   #50
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Great info here thanks for the sticky
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Old 04-14-2016, 01:42 PM   #51
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Thanks for the info.
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Old 05-01-2016, 08:58 AM   #52
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Great post. Some information on human vision from my perspective as a TV engineer might add some more light to the discussion.

In American the NTSC TV signal (the old 640x480 resolution) had a refresh rate of 30 frames/60 fields per second and most people don't see flicker with it. The PAL standard common in Europe and elsewhere used a 25 frames/50 fields per second rate and I heard a few people complain - mostly Americans. Film projected is shot at 24 frames per second. These field rates were chosen to match normal human persistence of vision - the amount of time the image remains on the retina. With white light it's very noticeable and back when we had big CRT tubes for our computer monitors some would notice and complain about their white word document pages flickering at the 60 hz refresh rate. Boosting the refresh to 72 hz normally solved that problem if that rate was available.

I would guess the PWM for the Jeep headlights has to be around 40-50 hertz which is pretty darn low because people are noticing it. LEDs are capable of flashing on and off at rates thousands of times faster. A simple capacitor designed to the refresh rate time constant would "slur" the square waves pretty well.
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Old 05-04-2016, 01:50 AM   #53
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TVs were run at 60Hz because the AC frequency is 60Hz in the US, and in countries where the AC frequency is 50Hz, their TVs were run at 50Hz. I suppose that saved money since you didn't need to include timing devices in the TV's electronics. -shrug-

PWM circuits are often run at some fraction of the frequency of the processor or bus they are controlled by. Yeah, a capacitor would probably do the trick.

At some point I'd get super lazy and get an embedded board that can listen for the canbus signal to turn on/off the headlights and just use that to drive my own headlight control circuit, lol. Wait, that's the opposite of super lazy.
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Old 08-18-2016, 10:32 AM   #54
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So what I don't understand is why then my LED lights (and HID for that matter) would not flicker when the engine was not running but would start to do so when the engine was started and all the chatter starts up on the CAN. I also had an interesting thing happen. I put truck-lites in a couple of weeks ago and mistakenly took the high beam power from after the anti flicker modules to drive the relay that turns on my light bars on high beam. This made the light bars flicker and the relay buz. Without the anti flicker modules the light bar problem went away but the truck lites would flicker after engine start (not before). Solved by taking power for the relay from before the anti flicker modules.
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Old 08-18-2016, 10:51 AM   #55
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Originally Posted by XKCOMMANDER View Post
So what I don't understand is why then my LED lights (and HID for that matter) would not flicker when the engine was not running but would start to do so when the engine was started and all the chatter starts up on the CAN. I also had an interesting thing happen. I put truck-lites in a couple of weeks ago and mistakenly took the high beam power from after the anti flicker modules to drive the relay that turns on my light bars on high beam. This made the light bars flicker and the relay buz. Without the anti flicker modules the light bar problem went away but the truck lites would flicker after engine start (not before). Solved by taking power for the relay from before the anti flicker modules.
The PWM flicker is a result of the alternator and other systems so the car being off the only draw is the lights there is nothing to cause the flicker.
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Old 08-19-2016, 12:13 AM   #56
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The PWM flicker is a result of the alternator and other systems so the car being off the only draw is the lights there is nothing to cause the flicker.
Right.

The CAN "chatters" even when the engine is off; even when your key isn't in the hole. If your lights are turned on, the interior CAN bus is talking to the TIPM who in turn is controlling the lights. Its just the way it works.
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Old 11-05-2016, 05:47 PM   #57
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So is there a way to fix this flicker? I'm not auto-savvy unfortunately, but my headlights flicker all the time when they're on. I don't have a ton of cash to invest into this just yet either so I was hoping for a fix for the stock lights in the meantime.
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Old 11-06-2016, 01:46 AM   #58
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Originally Posted by RavingLoonatik View Post
So is there a way to fix this flicker? I'm not auto-savvy unfortunately, but my headlights flicker all the time when they're on. I don't have a ton of cash to invest into this just yet either so I was hoping for a fix for the stock lights in the meantime.
an anti flicker harness, you can get one for a reasonable price on amazon
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Old 11-06-2016, 01:31 AM   #59
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Originally Posted by dcgibbons View Post
Right.



The CAN "chatters" even when the engine is off; even when your key isn't in the hole. If your lights are turned on, the interior CAN bus is talking to the TIPM who in turn is controlling the lights. Its just the way it works.

I have seen this when I installed a pair of LED spot lights to the fog light connectors. The lights would flash on very briefly every 45 seconds or so. This is the system checking the fog lights for an open circuit and occurs with no key in the ignition. I fixed it with a circuit I made with a capacitor, resistor, and diode. This was before I knew there was such thing as an anti-flicker adapter.
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Old 11-06-2016, 03:04 AM   #60
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Wow great info, I'm surprised I missed it.

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