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Can somebody please explain this DRL lighting circuit to me?
Hello everybody. It's been a long time since I last posted about anything.
Below is what I believe to be the wiring diagram for the lighting circuit for a 2002 4Runner with DRLs. Is that correct? I'm not sure if there was any difference between the Canadian 4Runner lighting circuit and the US one in that year but FWIW, my 4Runner is a Canadian car so has DRLs.
For starters, does anyone have a higher res version of this diagram they could share or please point me to where I can find one? I've looked around a bit and haven't been able to find anything better than this one as of yet. I searched this forum and downloaded a different 2 page version of this diagram from another thread in this forum but the resolution is also not very high. If you zoom in on it enough to be able to read the text in most places, the text is so pixelated and blurry you can't read what it says.
Second of all, I was wondering if someone could give me a general overview of how this circuit works? I am an engineer so I have some idea of what's going on (i.e. I understand how relays work and all that) but I'm not an electrical engineer so my ability to understand everything about how this circuit is working is not there.
Here's the reason I want to know more about how this circuit is working. I have another (non Toyota) car from 2008 that uses H13/9008 type headlamp bulbs and I replaced them with a high quality 6000K LED bulb that was designed to mimic the filament placement and light spreading characteristics of the H13/9008 bulb and the conversion worked great. The light pattern was exactly the same as it was with the OEM H13/9008 bulbs (I checked this to make 100% sure), my DRLs work perfectly and there have been no issues whatsoever with the conversion/ugrade. The only real difference is that I have much more light and can see a lot better with the LED bulb replacements. The 6000K coloring is a decent pure white and although it is cooler than the OEM bulbs, it has none of that annoying blue tint that higher K bulbs have that make it very hard for oncoming drivers to see well. I hate those things and wouldn't use them in my car.
I would like to do the same thing with my 4Runner because the stock H4/9003 bulbs don't put out a lot of light and I'd like to try replacing them with a properly designed LED replacement that again, is designed and constructed to mimic the light pattern of the H4/9003 bulb. I'm hoping I will have as good of a result as I got with LED replacement bulbs on my other car.
In doing the research on doing such an upgrade on a Gen3 4Runner on this and some other forums, I read that there could be some issues with the switch and that I might have to make some modifications to the lighting circuit make everything in the lighting circuit work normally again after dropping in the LED replacement bulbs. These possible issues include, the DRLs not working and the high beam indicator light not working but I believe at least some of these issues were with US non-DRL Gen3 4Runners which have a different lighting circuit than my '02 DRL 4Runner.
Has anyone installed these lights or something similar on their '02 DRL 4Runner? What issues did you have if any? What problems/issues did you to have to overcome and what did you do to remedy them?
Okay. For some reason Amazon sent the lights to me on Prime even though I do not have a Prime account and did not take the offer of free Prime for 30 days with the purchase so I got them today instead of Thursday when I was expecting them to arrive. The first chance I got, I went out and installed the lights and answered my own questions about what issues I'd be facing if I swapped in those LEDs for the H4s and did nothing else to the lighting circuit. Here's what I found out:
DRLs work but they flicker a little. I don't know if it's enough to bother anyone driving around in the daytime. Brightness seems to be about the same as low beam.
No flicker when headlights turned on and set on low-beam.
High beams work fine and high beam indicator in instrument cluster is lit when they're on. No flicker on high beams either.
No report yet on beam pattern. Will have to go to a place where I can part 20 feet in front of a vertical wall after it gets dark to assess. Will use that opportunity to adjust the aim of the headlights if needed. Will report back.
Color of beam is pure white, no bluish tint at all. Glad I chose lights that were 6000K and not 6500K.
Assuming the beam pattern checks out okay and is just like the original beam pattern, it would seem then that the only issue is the slight flicker of the DRLs. It's not that serious or noticeable so I could probably get away without doing anything about it but I'd like to fix the problem if I can. What's causing that to happen? Does Toyota pulse the DRLs to make them a little dimmer than full on low beams? The DRLs use the high beam filament don't they? Are there any possible remedies for the DRL flicker (besides going back to the original H4/9003 bulbs)?
So why are the DRLs flickering? Is the current to the DRLs being pulsed to produce a dimming effect? If yes, what device is doing that? Where in the circuit diagram is the pulsed signal coming from? What wire is carrying that signal?
If the signal being sent to the DRLs is pulsed, I'd like to find a way to replace it with a solid signal sent through a resistor to dim the DRLs. I may have already found a way to do that on YouTube but I need to understand the circuit better and I'm hoping someone here will be kind and generous enough to help me better understand how this circuit is working. Please and thank you.
Okay, I managed to find a complete FSM for Gen3 4Runners on-line and have extracted the schematic for the '02 4Runner headlight circuit with DRLs and an explanation of how the circuit works. I have attached those 4 pages to this post in PDF format. I now have a basic understanding of how the circuit works. I don't think they could've come up with a more Rube Goldberg setup for that circuit if they tried but maybe I just don't understand all the thinking that went into its design.
From the explanation in the pdf it appears that the DRL circuit actually uses the low beam filaments of the headlamp bulbs and not the high beam filaments as I've seen stated in so many places. Did I understand this correctly?
It says, however, that when the DRLs are on, the headlights light up dimmer than full brightness but it does not explain how that is accomplished. That is what I want to know.
So, after learning all this my main questions are still unanswered: How is the dimming of the DRLs being accomplished and what in the circuit is doing that? And how does this relate to why my DRLs flicker when I put in LED replacements for the original H4s? Is the current going to power the DRLs being pulsed? If yes, what's doing that? My hunch is that it would have to be D8, the main DRL relay but that's just a guess.
If anyone wants the link to this 2,153 page FSM that I found online, let me know and I can post it. The cover of the FSM says it's for all years of Gen3 but at the bottom of each page it says 2002 4Runner so I think what I've got is just the part of the manual that's for the 2002. AFAIK, 2002s weren't much different than 2001s so this manual should be useful for 2001 owners too. I don't know enough about these cars to know what the differences are between 2002 and the '96 - '00 4Runners and how applicable this FSM might be to them.
I will try to help. I have read a lot of these ewd's from toyota and fixed a lot of wiring issues.
I see where toyota states that the drl have reduced output. The only way I see this could happen is if the D9 daytime running light relay stays OFF. Thus the ground for the headlight bulbs will then go thru the D8 DRL light relay (main). Then a resistor in that relay will dim the bulbs. I don't think it is pulsed, I think its a standard resistor built into that main relay. When you turn on the actual headlights, the D9 daytime running light relay energizes, and thus gives the bulbs a straight shot to ground.
If you want to spend the $20 you can get these diagrams and all the other repair manuals direct from toyota. techinfo.toyota.com
I will screen shot the drl power circuit highlighted.
Thank you for your help, @BBQ Tables . I believe you may be correct. I read very carefully the description of how the circuit works in the pdf I attached to my previous post and it says that when the DRLs are on, the circuit grounds through Terminal 1 to Terminal 2 to ground through the D8 DRL Relay (Main) but when the headlights are turned on, the circuit grounds through DRL Relay no. 4 Terminal 1 straight to ground. From that I would deduce that whatever is dimming the DRLs is between Terminals 1 and 2 on the main DRL relay (D8). That could indeed be a resistor. I'll have to put the meter on it when I have time to examine that relay.
The curious thing about their description of the circuit is that they do not mention how Terminal 6 of the main DRL relay and the red wire between that terminal and Terminal 3 of the Head Relay are used. Does that power the DRL Relay (main) after it is first activated through the parking brake switch?
At any rate, if the difference between the two lighting circuits is whatever is between Terminals 1 and 2 on the main DRL Relay and if that's just a resistor, do you think my DRLs flicker when the LED replacement bulbs are installed because they aren't quite getting enough current or voltage because of that resistor's in the path? If that's the case, I could potentially solve that by adding a wire with another resistor in between those two terminals (a parallel pathway) to increase the amount of current going through the circuit to where it's just enough to prevent the LEDs from flickering but still less than full power to keep the DRLs from being full brightness.
Terminal 6 is a ground from the main relay box to the headlight relay to power the headlight bulbs, either when the drl are needed (parking brake off, engine on), - or - when the headlight switch is turned on (but it will probably already be on due to the drl).
That red wire is actually a ground since the load is inside the relay.
Its down further in the system outline section and also the service hints.
Yes you should be able to test the voltage drop and resistance between 1 and 2 of the main relay to get an idea, or check the voltage at the bulb on drl function to see if it is close to the spec for the LED's, some are dimmable, but I don't think many headlight bulb LED are dimmable...
Adding another resistor in parallel will decrease the total resistance and increase the voltage. Or remove the W-G wire and use your own resistor to ground, as the lights will shut off when the head relay shuts off.
Just unplug the connector near the driver headlight and battery, it will disconnect the DRL, DRL does run at a lower voltage. I'm not a fan of LED as the headlights ice over and typically LED in a Halogen bucket don't mix, Auxito has excellent sales team I see. I went the 80/100W Hella and wire harness route, and added the fog lamps anytime option.
Okay, so I finally got out and did a little bit of investigating today. I discovered that when the truck is n DRL mode, there is a steady (no pulsing) 11.3 volts going to the low beam filaments or LEDs in my case. When the headlight switch is turned on, it's 13.2 V (or was it 13.5 V?) going to the low beam and if I turn on the high beam it's 13.2 V going to both the high and low beam filaments/LEDs. So it appears to confirm that the DRL Main relay dims the DRLs by means of a small resistor that drops the circuit voltage down to ~11.3V. I haven't pulled that relay out to measure the resistance from terminal 1 to 2 yet so I don't know how many ohms that resistor is but I suspect it's not a very big resistor.
Auxito customer service was nice enough to send me a set of Can Bus Decoders for free and said they should eliminate the DRL flicker problem. I was skeptical of that but thought I should give 'em a try anyways so I did. Much to my surprise, they worked! Flicker on DRLs is now completely gone! Voltage going to the low beam filaments/LEDs in DRL mode is now 13.2 V and same for headlights switched on in low beam mode. So as it stands, I have no more flicker in DRL mode but my DRLs are slightly brighter but are only at full on low beam brightness so not near as bright as full on high beam brightness. During the day, I doubt that ~2 volts worth of extra brightness will make much of a difference to oncoming traffic and when it gets around near dusk I always switch my headlights on so my tail lights are on so there would be no difference then either. I'd be at full low beam brightness either way and that never seems to bother anyone.
To get the system perfect, I can measure the resistance between terminals 1 and 2 on the main DRL relay and try grounding the green and yellow wire going to Terminal 1 through a different resistor to see if I can get the DRL voltage down to maybe ~12V to dim the DRLs a wee bit below full low beam brightness but still keep it high enough to prevent the LEDs from flickering.
Before any of that though, I need to take the truck over to a place where I can park it 30 feet from a vertical wall and evaluate the beam pattern to make sure it's as close as can be to the beam pattern you get with the standard H4 bulbs in. If the beam pattern checks out okay, I'll keep running with the LED bulbs but I'll try to dim the DRLs down as much as I can without causing any flicker. If the beam pattern is crap, then I'll scrap the LEDs and go back to using H4s and look at other alternatives to make those headlights a little brighter.
Now that I think of it, I don't quite understand how the Canbus decoders got rid of the flicker and bumped the voltage getting to the headlamps up to 13.2 V in DRL mode. Can somebody please explain that to me?
11-27-2023, 12:29 PM
