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The Saga of the Left Cornering Light and the Solution

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I've posted several things on here regarding the perpetual "Check Left Cornering Light" error on my 2004 Cayenne S. I have now, after hours and hours of troubleshooting, figured it out... better yet, I think I know why it has been such a perpetual, intermitent issue even though the dealer had seen it three times (under warranty at the time). Each time, and the first two times I tried it, the light bulb was replaced, sometimes with success, sometimes not. It might work for a few trips, but then would start erroring again... back to the dealer (or my garage), replace the bulb, pray for success and so on.

I want to note that I changed out the wiring harness for the headlight assembly (for both left and right) and that did not make the issue go away. The reason I did that was because one of the clips was broken on each side (presumably by the dealer when they were working on it, but hey, why tell the customer if you broke something they can't see). On the bright side it ruled out the wiring harness being the issue and satisfied my anal rententive nature to not have anything broken (seen or unseen).

The second thing I noticed was that my side/parking/running lights (seems they have a lot of names, it's the W5W bulb directly under the headlight) were both burnt out on each side. The car wasn't yelping about that though, but since they share a wire with the cornering lights I thought that might very well be relevant. It sort of is in a way... the car determines if the there is a problem with a light bulb by measuring the OHMs (which I read elsewhere on this forum), it seems to be very sensitive to that and will declare the bulb dead at the touch of an issue. I replaced the bulbs, but the left cornering light issue was still present.

Now, for the real solution... which, kind of stupidly, all has to do with putting the headlight assembly back in place.

When replacing the assembly (and I know this seems obvious but the dealer was screwing this up too), you have to REALLY get it put back in place. On the bottom of the assembly, you'll see a little hook molded there right in the center where the metal bar is supposed to hook into. However, it is possible (and apparantly likely) to replace the assembly, turn the little lever and assume everything is back in place... I did at least a dozen times while screwing with this. You can even tug on the assembly a bit and it all feels snug... only it's not.

It takes a lot of faith, but what you have to do is push down and in on the assembly with a little bit of force (mostly just to hold it in place... don't risk breaking the clear plastic). At the same time, you have to turn the tool towards "lock" with a strong degree of force... a lot more than you will probably be comfortable with. Once you do that, you'll hear a very disheartening "snap" and at that point everything is back in place as it should be.

As an FYI, when removing the headlight you hear the same snap.

If you get a reallly bright flashlight, you can actually peer underneath the headlight assembly and see all of this take place... there is about a 1/8" gap there if everything is aligned right.

I know this may seem brilliantly obvious to a lot of people out there, but since I never ran across the solution anywhere on the 'net I figured I would post it.

Now error code free,


Edited by jharness
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I can confirm the reluctance to turning the tool hard enough to get the snap. I swear when I heard it I thought I had broken something. Until it snapped into place I was getting lots of errors sometimes induced by simply driving over a bump.

Once it "KAAAA BLAMMMMMED" into place all has been well.

So did the dealer never get it seated properly this whole time?

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Nope, they sure didn't. Once it went out of CPO warranty I started looking at it. I probably could have argued with them to still cover it, but the dealership is WAY out of my way and dealing with a loaner car kind of sucks as well. I just got tired of them so I decided to troubleshoot it myself. I'd get frustrated and just leave it alone for a month and then come back to it when I had another idea of what to do.

I should point out that each time I took it in to the dealership it wasn't just for the cornering light... I was always getting 3-5 little things fixed as well or an oil change. So I'm sure they were just changing the bulb, testing it without driving it and calling it good.

I did see the same behavior as well when hitting a bump, that would kind of kick it into erroring out even if I thought I had everything seated properly.

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