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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 5783
Experience:  GM Grand Master Technician 2007. 14 years experience.
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GM Yulon xl: 02 yukon xl 1500 2wd. The problem started with

Customer Question

02 yukon xl 1500 2wd. The problem started with by low beams suddenly not working one night. The next night they worked. Took it to have it checked and they could not find any problems, but replaced the relay just in case. The problem progressed to where they do not come on at all anymore, nor do my DRLs, only parking lights (which seem very dim), and the high beams work. I had it checked again and was told it was the ambient light sensor and that the dealer has to fix it. I took it to the dealer and they thought said the diagnosis was unheard of and they did nothing. I've looked online for further troubleshooting and saw that there is an ambient light sensor that is located behind the radio that could be the problem or else a grounding issue. I just called the dealer and they said they've never heard of such.
I'm selling the vehicle tonight and would like to give it my best shot to get the light working. Any suggestions? Where do I check the ground wire under the hood?
Submitted: 1 year ago.
Category: GM
Expert:  GM Tech (Cam) replied 1 year ago.
Hi there, I am Cam. Sorry for the delay in getting to your question. Can I get your first name please? Can you also tell me if tilting the wheel up and down seems to change if the lights work or not?
Customer: replied 1 year ago.
Kristen...
No tilting the wheel does not change whether the light work or not
Expert:  GM Tech (Cam) replied 1 year ago.
Kristen, one moment while I study the schematic to see if it sheds any clues on what to test. In the meantime, can you tell me if the dimmer switch feels perfect or does it seem even slightly different than before?
Customer: replied 1 year ago.
I honestly have always left the dimmer switch in the auto on position. When I had this issue checked the first time, they told me that the dimmer switch may just need to be exercised more. To me it seems normal. This issue has been ongoing for 6 months so I've tried exercising it to see if the lights would work. Here's another thought for you. Before they stopped working completely, I was able to crank the engine, open the hood, then either tap on the fuse box or barely remove the cover and they would come on...but while driving they would go off for about 3 seconds then come back on about every 5 minutes. I've also noticed recently that the hood lamp is sometimes on and sometimes off. When troubleshooting yesterday the hood lamp came on when I opened the hood. After checking that the headlight bulbs weren't burned out, i noticed that the hood lamp was off...and would not come back on.
Dash lights, rear lights, inside lights etc...work fine.
Customer: replied 1 year ago.
it seems maybe I'm not getting power from relay to fuses? When engine powered off and dimmer switch turned to on position (not auto) the light on alarm does sound
Expert:  GM Tech (Cam) replied 1 year ago.
In your glove box is a sticker, on that sticker, do you have code Z75?
Customer: replied 1 year ago.
I need to go off line for a few and I'm not near the vehicle. My friend Spin is at my house where the vehicle is located. He checked and there is not a Z75 code. Z88 AND Z82
I'm going to enter his phone # ***** the call me box. I'll let him know to expect your call.
Expert:  GM Tech (Cam) replied 1 year ago.
Thats fine, without is what I needed to know, .
Expert:  GM Tech (Cam) replied 1 year ago.
Sorry I meant to accept the offer. IF you can request it again I can call.
Expert:  GM Tech (Cam) replied 1 year ago.
But looking at the wiring and schematic, if the high beams work properly meaning both the flash to pass and simply pulling back and releasing, then it is most likely the dimmer switch or the wiring from the bulbs to the dimmer switch. the system applies power to the bulbs directly through the relay, then a ground path is provided through the dimmer switch. SO provided the wiring and bulbs are good, its a switch. The test i would do is this. I would turn the lights on then at the dimmer switch in the steering column, I would manually apply a ground to the yellow wire beside the purple to see if the low beams do come on. If so then your dimmer switch, properly called the multifunction switch is bad. They are a common issue on these.