Why are my headlights blinking off while driving?
October 16, 2009 9:20 AM   Subscribe

The headlights on my 2004 Dodge Durango randomly blink out for a few seconds while I'm driving. As you can imagine, this is a bit unnerving, not to mention dangerous, on a dark road at night. It is not consistent. It may happen a few times one night, then not again for a week. I do not have the automatic headlight feature. It does not seem to be connected to using the brakes, or turn signals, or anything like that. It's not even connected to moving as it has happened while the truck is not in motion. The 2nd generation Durango's do not have a headlight relay, which was my first thought on a part to check. The lights are apparently digitally controlled. I took it into the dealer and of course, the damn lights wouldn't act up there and the on board computer is not reporting any error codes, so the dealer didn't do anything but overcharge me for an oil change and tire rotation. I'm worried the lights will go out for good at a very inopportune time, like on one of our two trips in the next month. Has anybody had this problem, or have a guess as to where I should be looking for the cause?
posted by COD to Travel & Transportation (8 answers total)
Two probable causes:

the bulb is ready to go--get it replaced
bulb is loose due to being hit ---get it replaced

I've had this happen on my 04 Maxima. Both reasons were the cause.
posted by stormpooper at 9:22 AM on October 16, 2009

Point of clarification - both headlights blink out together and come back on together.
posted by COD at 9:38 AM on October 16, 2009

posted by Oireachtac at 9:45 AM on October 16, 2009

It's a long shot, but there's a TSB for that year Durango pertaining to a fuse that's incorrectly installed, resulting in intermittent loss of power to some accessories. Upon a google search, more details about which fuse and where it is weren't exactly forthcoming. It's Dodge TSB #0800704, if you care to do a more extensive search yourself.

If the lights are cutting out entirely and not flickering, I'd be somewhat inclined to start ruling out a loose connection. If you smack the plastic headlight housing, a loose connection will typically cause a flicker at that point. I'd start looking for a bad switch or other input to the control module that runs the lights, if that's how the circuit is set up. If the control module receives a signal that the switch is off and correspondingly turns the lights off, it won't store a fault. It thinks everything's working fine.
Now, since it's a digitally controlled system, there's a chance that the switch isn't current bearing. That is, it's voltage coded and, instead of the current flowing through the switch like a light switch in your home, it's more like a switch position sensor whereby the control module sends a small reference voltage to the switch and each switch position has a corresponding resistance that the control module measures and then provides the corresponding illumination. These systems are increasingly common in automotive applications since it reduces the amount of wiring in the vehicle, especially the amount of high-current wiring in the passenger compartment.
If there's a problem with the reference voltage, the control module might be getting an erroneous signal. However, that will certainly cause a fault code to set. Most control modules keep a close eye on their own supply voltage and will store a fault if it's inadequate.
But, if the supply voltage to the control module cuts out entirely, it'll shut the headlights off and likely not store a fault, since there'll be no power available to operate the computer.

Like I said, it's a long shot, but check to make sure all the fuses are correctly seated per the TSB. If one of them is loose, it could provide power just fine until jostled enough to break the connection.
posted by Jon-o at 9:49 AM on October 16, 2009 [1 favorite]

That's going to be tough for the dealership to troubleshoot. Maybe a wire's shorting out somewhere. A good test would be to take the vehicle out at night, drive it on a smooth surface, then a bumpy surface to see if that makes a difference.

I'm not quite sure what you mean when you say the lights are digital, but there's usually a fuse somewhere. You might want to track that down and make sure it's in firmly, or replace it altogether.

Also, I've found that it's possible to find answers for problems like this on web forums that are specific to your vehicle. Here is what a Google search yields.
posted by SteveInMaine at 9:51 AM on October 16, 2009

Yeah, I asked at Dodgetalk.com first - got pretty much the same answers there that I'm getting here.

Thanks for the info on the TSB. Agreed it's a long shot - but worth following up on. I can't find the full TS online, not for free anyway. However, I'll bet somebody at Dodgetalk has a subscription and will send it to me - they do that all the time there.
posted by COD at 10:13 AM on October 16, 2009

because of the difficulty in determining the actual cause of this problem, it may be simply cheaper to replace all of the affected hardware. not sure how much that would involve, but I would probably replace the fusebox, and all of the wiring from there to the headlights. I'd also replace the interior switch--the one you use to turn the lights on.

but i'd check jon-o's tsb first.
posted by lester's sock puppet at 10:26 AM on October 16, 2009

Regardless of your headlights being digitally controlled there has to be a relay somewhere to handle the high current switching. It might not be the traditional mechanical relay under the dashboard. It might be an electronic relay switch that is near the headlights.

As Jon-o says, your headlight relay, mechanical or electronic, might not be controlled directly by the driver's light switch. The light switch might send a signal to the computer and the computer actuates the relay. I would look first at the driver's light switch and wiring going into the computer. Then I would look at the wiring from the computer to the relay and the relay itself.
posted by JackFlash at 2:41 PM on October 16, 2009

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