[martinma899]

Hi everyone, thanks for taking your time to read this.
I've had a fair share of troubles working with my aftermarket headlights. A little background: last year I installed aftermarket headlights on my 2012 accord sedan EX-L 4 cyl. The headlights use H1 bulbs for high and low beam. I then bought some H1 LED beams to make my accord look sexy.
Then when I was installing my left low beam LED, due to probably a design flaw in the aftermarket H1 LED, there was a short between the light's positive and ground at the light's base. That blew my left low beam fuse. I then figured out the short and replaced the fuse, and the low beams ran ok for about 8 months. However they were quite dim, both the left and the right, from that point on. Not at all as bright as the high beams, which were the same bulbs. I didn't think much of it. I thought it was just a design problem in how the headlight's lens doesn't work as well with this kind of LED. Also I swapped in fog lights from V6 model parts, so the fog light's been compensating for the very dim low beams.

Jump to a week ago, when my left low beam completely went out. I thought no big deal, maybe just a bad connector. So I worked on testing the light connectors and all observable wires behind the headlight. Nothing, all no resistance, all continuous. I tested the LED bulb by itself on a 12V source, works very well. I do get 12V sometimes at the light, and sometimes I don't. When I do get 12V, the left low beam is very dim. As my testing went on I noticed my right low beam is also getting dimmer than before.

Then I tested some more, and found some weird results:
I installed a halogen H1 bulb on the left low beam that I know is good. That instantly blew the low beam fuse.
I replaced the fuse, put the H1 LED bulb back on, disconnected the car battery and let it sit for a few minutes. When I connect the car battery again and turn on low beam, the left low beam becomes very bright, the normal brightness you'd expect. The right low beam is still dim. I turn off the light and on again, left low beam becomes dim or completely cuts off. That tells me it simply can't be a connectivity or bulb problem. If so then it is impossible for the bulb to suddenly return to normalcy.

All of these testing lead me to think that it is an MICU problem. By shorting my left low beam circuit 8 months ago I probably damaged the low beam control circuit, which made the low beams dim. Now it is finally giving out. But if I disconnect the battery and let it reset, it can somehow magically muster out a little more life and normalcy.

I guess the question is, can short circuiting your low beam and blowing the fuse damage the MICU low beam control modules? Anyone experienced this?
I have an HDS system and I will be running the MICU tests tomorrow.

Edit: likely not the combination switch's problem. I replaced the combination switch with a known good one and made no difference.

Thank you.

 

[Miker]

My first thought is that the circuit for the low beams is used for DRL.

Is that true on the 2012? The low beams run at < 100% when used as DRL's but run at 100% when "turned on" ?

Maybe the new H1 LED's don't like to be run under powered (if my question above is true) and are affected by this.

 

[a1smith]

My first thought is that the circuit for the low beams is used for DRL.

Is that true on the 2012? The low beams run at < 100% when used as DRL's but run at 100% when "turned on" ?

Maybe the new H1 LED's don't like to be run under powered (if my question above is true) and are affected by this.

According to the service manual, the DRL circuit pulse width modulates the voltage to the high beam headlights.

 

[a1smith]

All of these testing lead me to think that it is an MICU problem.

I have an HDS system and I will be running the MICU tests tomorrow.

Here is the link to the service manual if you don't already have it.

Honda Accord 2008-2010 Service Manual (Downloadable PDF)

Here is the service manual if anyone wants it. Downloadable PDF

www.driveaccord.net

Exterior Lights starts on 22-200

Low beam circuit description on 22-206 - note that driver's MICU controls left low beam and passenger's MICU controls right low beam (after driver's MICU sends it CAN message to turn on low beam)

It seems like there are multiple DTC's for the headlights - have you checked to see if any of those are present? The service manual lists them and outlines actions to take for all of them starting on page 22-216.

There is a MICU Input Test starting on page 22-226. They tell you to troubleshoot MICUs first using B-CAN Diagnosis Test Mode A (page 22-134). You need the HDS to do that so you're all set.

 

[martinma899]

There is a MICU Input Test starting on page 22-226. They tell you to troubleshoot MICUs first using B-CAN Diagnosis Test Mode A (page 22-134). You need the HDS to do that so you're all set.

Hello, thank you so much for your reply.
I have checked lighting codes with an HDS system same as the dealer's. Unfortunately no lighting codes at all.
I have the factory manual. I'm stepping through it at the moment.
I will try the MICU trouble shoot procedure and see what I find.

 

[martinma899]

According to the service manual, the DRL circuit pulse width modulates the voltage to the high beam headlights.

The high beam 100% mode and daytime running light mode have been working fine. It occasionally throws a DRL warning light when in DRL mode, but generally the high beam LEDs are working normally at 100% in high beam mode and they are dimmer in low beam mode. That has been normal.

 

[martinma899]

Hi everyone, I think I figured it out. Yesterday I forgot about something I did back in January. I remembered it just now. When the 10A left low beam fuse first blew back then due to the short at the base, me being very stupid, put a 30A fuse in the low beam circuit, and then proceeded to blow the 30A fuse due to the persisting short. Basically I ran 30A through the left low beam control module where the fuse is 10A. I know this is the very fundamental principle of never put a bigger fuse than specified, but I learned it the hard way. The left low beam circuit's components probably got burnt up which could not supply the proper current. It is a miracle that it lasted 8 months before completely going out. Considering the lighting circuit is usually 18 gauge wires, they are not rated for handling 30 amp either, so there might be harness damage too. However the wires I did check were all good and there were no signs of burning.

I did use the HDS to test out all kinds of light signals. The MICU is sending the correct signals of light on/off and nothing wrong observed there.

I will be trying out swapping the driver's side fuse box/MICU first.

Let my story be a tale of warning. But you learn by making mistakes I guess.

 

[mtts60]

I would not start with the MICU at this point, you said it was working. If you have a wiring diagram, find both ends of the low beam wire(s) and check for continuity. Once you find a bad wire, splice in a jumper and see if that fixes the problem.

 

[martinma899]

I would not start with the MICU at this point, you said it was working. If you have a wiring diagram, find both ends of the low beam wire(s) and check for continuity. Once you find a bad wire, splice in a jumper and see if that fixes the problem.

Thanks. Looked at the circuit diagram, the left low beam power wire runs from the low beam headlight connector to driver side MICU port F21, red/yellow wire. If that wire is good then it's new MICU time

 

[mtts60]

That's good, but don't forget the wire from the MICU to the affected headlight.