Strange LED Headlight issues

[Xedos9er]

Hello,
I have a very strange issue with my LED headlight on my 2015 PCX (european Version). Sometimes my low beam light switches off, when i turn on the turn indicator. Today i noticed, that my low beam was all the time off, till I switched on and off the turn indicator. After that it worked fine, till i switched on the hazard lights. At the moment it turns off, when i switch on the hazard lights, but not every time. Also strange, when hazards are on and low beam doesn´t work, it turns on, when in turn on the high beam, but switches off again when I switch to low beam.
What´s going on here? I already exchanged the LED Control Unit, looks like it did not help at all??

I also checked all the plugs, they look fine. The pcx has only 500 miles

[PCX150Rider]

A call to an "Exorcist" perhaps?

Seriously though. . .that is one far out set of problems.

You are from where? Europe you say? The U.S. version doesn't get the "hazard lights" although would be nice to have.

Since the symptoms are so varied and fluid I'm thinking the problem could perhaps be caused by an intrusion of water somehow causing short circuits. Did you use a high pressure hose or power washer on your PCX recently. . .or leave it outside in harsh wet conditions for a long time?

Time for the experts to jump in here. . ..

[Mel46]

Hmmm... There is something going on that is common to both the headlights and the hazard lights. Perhaps you can get an indication of some kind by looking at the wiring diagram. Attached is one for a 2014 but it looks like it is for the LED version, so it should be fine.

Honda_PCX2014_wiring.pdf

(67.41 KiB) Downloaded 234 times

[Xedos9er]

Hi,
I already checked the wiring diagram, the turn indicators/hazard lights use the same ground like the low and high beam for switching on and off. Since the low beam is permanently on, it just uses a bringe from the L_GND output pin to the LO IN pin. I checked this bridge by opening the wiring harness and measuring the resistance. Btw, i understand now why the Low beam is working when switching on the high beam: if the LED Control unit is seeing ground on the HI IN pin, it outputs automatically on both outputs LO and Hi out. And if the Low beam is failing I also see, that there is no voltage on the Output pin, that means the control unit somehow sees no ground on the input pin, bit the connection is fine and the control unit got exchanged by a used one

[Mel46]

Check the wiring itself to see if there is a intermittent short or ground. It could be a loose wire or the ground wire is broken but is still connected at the ground point, which would cause intermittent connections. Also check for corrosion in the connectors, and run the wires to make sure none of them has rubbed the insulation off. The ground is common to both hi and lots beam.

Also check the dimmer switch. Which reminds me, the gray/blue wire goes to plug "6P BU" and dissapears in the wiring diagram. It eventually attaches to the ground for the turn signal. (Check that connector.) Assuming that it turns into a ground and goes to the LED Control Unit, it could mean that the dimmer switch is going bad or the Control unit. Since you already tested the Control unit see if you can borrow a dimmer switch and plug it in instead of the one on the bike.

[cessna151]

Just throwing this out there... Are you making observations of the actual headlight itself or just the indicator on the dash? Perhaps the dash indicator is faulty.

[Xedos9er]

It´s the headlight. The low beam has no indicator. At the moment it´s working again. Last time i removed all insulation tape on the wiring to the LED Control Unit connector to check the wiring. Did not see anything, but to get sure I recrimped the bridge (see attached screenshot).
Seems like it´s working now. I think it´s a matter of time, till it fails again. I ordered an used wiring loom, if it fails again, I will exchange the whole wiring loom. Don´t have the time to do more time consuming failure investigation.

[Mel46]

I believe that any wires in the Honda wiring diagram that have green as their base color eventually go to ground. That means that the one you circled goes to ground somewhere. Just FYI.

I am glad that you have it working now.

[Gil]

Check the plugs for rust, I installed a used wiring harness for the turn signals into my USA PCX, this pass summer. After the install I noticed that the light bulbs weren't working, it turned out to be rust on the ground wire to the bulb socket. So, check your plugs for rust, any surface rust might cause weird side effects.

[Mel46]

...and that is what I have been trying to point out. Plugs are notorious for holding water, which causes corrosion. When I was in the military I spent two weeks trying to trace down an electrical problem that turned out to be an unrelated plug that the wire just happened to run through. Water had gotten trapped in the plug some how and was causing corrosion, which sent the signal to all sorts of different places.