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I'm in Lakeland Florida.

I am in Pinellas county if you get in a pinch. Not too close . but not to far either.

I am trying to remember if there was another post recently similar to this issue ??


* It was a high beam problem on a 7th gen camry. Turned out to be a fuse issue.
 

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Are you using a meter to verify if there is power coming to both the fuse input & output, if not to the relay terminals. If not I strongly suggest you get a meter.
 

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It would be helpful if posters would put some demographics on the year, and trim level of their highlander, as well as overall area they live in...
Not sure about trim (or how that affects ) , but the op mentioned in the first post it is a 2010 highlander.
 

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Guys, please check your years. All the wire diagrams posted so far are 2011+ with separate high and low beam bulbs. 08-10 uses a different architecture for switching the H4 bulb. There was some confusion about the 2011 diagrams above though, just know they use a mosfet (see below) to control the DRL on the high beams. The mosfet can act like a relay or do PWM (pulse width modulation) to run the bulb at 40% for DRL. The 08-10's do the exact same DRL strategy for the low beams.

Unfortunately this is not going to be an easy replace a relay kind of fix. If you have DRL's (and most 08-10's do), there are NO relays for low and high beam on the 08-10 highlander. That symbol is a mosfet (semiconductor...basically a big transistor/solid state relay) See attached wire diagram. Basically in blue is what you did when you connected 12V to the fuse, you bypassed the mosfet and backfed the other bulb through the parallel circuit.

If these have failed, you will be replacing the entire engine compartment junction block as the mosfets are not user serviceable parts (this is why I built a relay harness to protect the mosfets when I put in high power HIDs).

To get to the connectors your going to need to remove the fuse block from the car and partially demo it. I've never done it so can't give any advice there, sorry.
But:
-You know the bulbs work once your put 12V to the fuse, so everything downstream of the fuse is good.
-You know the ECU is good because the combination meter (edit: sorry old habit, that's the gauge cluster) is showing the high beam symbol.
-You need to check the connection between the ECU and the engine compartment junction block and make sure its getting the right signals from the ECU.
-----in the wiring block pic, I circled a wire and wrote a 1. That is the high beam control wire. That wire should be 12V to ground when the high beams are OFF and GND when the high beams are ON.
-----in the wiring block pic, I circled a wire and wrote a 2. That is the headlight (lowbeam) control wire. That wire should be 12V to ground when the low beams are OFF and GND when the low beams are ON.


If your inputs are good, and your output is good when bypassing and powering a fuse, that leaves you with only 1 option, the mosfet has failed and needs replacement.
Hard to believe those 'electronic' relays aren't plugin , as they are subject to failure as much or more than a mechanical type.
 

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Not sure about trim (or how that affects ) , but the op mentioned in the first post it is a 2010 highlander.
it's helpful when reading through a string of posts, to know what year/trim is being talked about. shouldn't have to go back to 1st posts in a topic to understand the relationship of what's going on...and trim helps too.


Seems most don't put this in their profile to show on every post.
 

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Discussion Starter #27
Are you using a meter to verify if there is power coming to both the fuse input & output, if not to the relay terminals. If not I strongly suggest you get a meter.
I have used a meter to verify that there is no power going to either fuse on the high beam fuses, either left or right beams, on both the input and output. I'm at a spot that I'm unsure how to proceed due to my own lack of knowledge. I'm not really wanting to take the fuse box apart to check the mophets just because I'm nervous that I couldn't get it back together. I did take the cover off the column of the steering wheel but I'm unsure how to test if the switch is working properly. I do know that when I activate the high beams the indicator on the dash lights up like they are on Also, the vehicle is a 2010 Highlander limited edition v6.
 

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Discussion Starter #28
it's helpful when reading through a string of posts, to know what year/trim is being talked about. shouldn't have to go back to 1st posts in a topic to understand the relationship of what's going on...and trim helps too.


Seems most don't put this in their profile to show on every post.
I just updated my profile. Thanks for the suggestion. :smile:
 

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it's helpful when reading through a string of posts, to know what year/trim is being talked about. shouldn't have to go back to 1st posts in a topic to understand the relationship of what's going on...and trim helps too.


Seems most don't put this in their profile to show on every post.
OK? Confused, would think one would at least read the first post describing the issue, let alone other posts afterwards showing suggestions. I have to admit where there are posts with lots of pages I don't read through them all either, but at least the first post from the op.

He updated as mentioned, but I don't see it ?? Do you have to click on his profile and look there? I do see his location now.
 

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I have used a meter to verify that there is no power going to either fuse on the high beam fuses, either left or right beams, on both the input and output. I'm at a spot that I'm unsure how to proceed due to my own lack of knowledge. I'm not really wanting to take the fuse box apart to check the mophets just because I'm nervous that I couldn't get it back together. I did take the cover off the column of the steering wheel but I'm unsure how to test if the switch is working properly. I do know that when I activate the high beams the indicator on the dash lights up like they are on Also, the vehicle is a 2010 Highlander limited edition v6.
Let me know about this. Not opposed to making a run or meeting halfway somewhere someday.

I need to research the electronic relay thing as seems weird that they are plugin replaceable. From what you posted already you have no power to fuses supplying power to high beams. You would need to find the wires to the electronic relay and measure there next. Harbor freight has cheap or free even digital multi-meters.
 

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I would suggest making sure there is either power from the pink wire connector 2D pin 9 and the black wire connector 2G pin 1. Also make sure that when you are testing this that the high beam switch is ON. If you are testing it off, you ain't doing much.
 

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Discussion Starter #33
I have the Exact same problem with my daughters High Beam...
Yes, I took it to a local mechanic and was told I need to take it to the dealership. Their scan tool couldn't see anything wrong. For now, we just do without high beams but I think about it all the time, especially when I'm driving it.
 
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