Odd headlight issue.
Thread Starter
Drifting
Joined: Mar 1999
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From: Mont Belvieu Tx
Odd headlight issue.
Here is an... odd.. one. My '99 Vette started to develop an issue where the passenger headlight would not come up every time I flipped the lights on. But sometimes it would. But, a few days after this started ... now when I lower the headlights (both previously UP), the passenger headlight lowers and continues to make a loud grinding sound for several seconds after to comes to the lowered position. It is VERY loud and noticeable (and sounds horrible). Also.. the odd part: Now, after this started happening, if I flip the light controls to the first stop position on the control-stalk, the headlights pop up but are not on. This is not the normal behavior. Normally it would just on the dash lights, fog lamps and parking lights... (which is nice because I don't like to always have the headlights UP when in semi-dim conditions). So.... Why in the world would the headlights pop-up on the parking-lights stop on the stalk... and why is that grinding sound occurring?
--Coyote
--Coyote
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St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16-'17,'19,'22
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St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16-'17,'19,'22
Yes that's a common symptom of the headlight gears failing.
The machine gun sound (the grinding sound you hear) is def. telling me that. Been there and done that. It's an easy fix.
The machine gun sound (the grinding sound you hear) is def. telling me that. Been there and done that. It's an easy fix.
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Got to agree - I'd bet the plastic gears in the headlight motors are shot.
Le Mans Master
Joined: Feb 2002
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From: Waldorf MD
I agree with all the comments, a common problem and easy fix.
The "whys" behind this are as follows:
The headlights use an electronic black box, called the headlight module, (located behind the passenger headlights) to monitor the current that the headlight motors draw, when the motors hit their stops (up or down), the motor current spikes and the box shuts off the current.
What happens is the plastic gears wear down and they "slip". This slipping causes the "machine gun noise". When they slip, there is no current spike, so the motor keeps going until a "time out" limit is hit. But by doing this the "timing" is messed up and sometimes the lights will come up when only the parking lights are turned on.
The "whys" behind this are as follows:
The headlights use an electronic black box, called the headlight module, (located behind the passenger headlights) to monitor the current that the headlight motors draw, when the motors hit their stops (up or down), the motor current spikes and the box shuts off the current.
What happens is the plastic gears wear down and they "slip". This slipping causes the "machine gun noise". When they slip, there is no current spike, so the motor keeps going until a "time out" limit is hit. But by doing this the "timing" is messed up and sometimes the lights will come up when only the parking lights are turned on.
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Thread Starter
Drifting
Joined: Mar 1999
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From: Mont Belvieu Tx
I agree with all the comments, a common problem and easy fix.
The "whys" behind this are as follows:
The headlights use an electronic black box, called the headlight module, (located behind the passenger headlights) to monitor the current that the headlight motors draw, when the motors hit their stops (up or down), the motor current spikes and the box shuts off the current.
What happens is the plastic gears wear down and they "slip". This slipping causes the "machine gun noise". When they slip, there is no current spike, so the motor keeps going until a "time out" limit is hit. But by doing this the "timing" is messed up and sometimes the lights will come up when only the parking lights are turned on.
The "whys" behind this are as follows:
The headlights use an electronic black box, called the headlight module, (located behind the passenger headlights) to monitor the current that the headlight motors draw, when the motors hit their stops (up or down), the motor current spikes and the box shuts off the current.
What happens is the plastic gears wear down and they "slip". This slipping causes the "machine gun noise". When they slip, there is no current spike, so the motor keeps going until a "time out" limit is hit. But by doing this the "timing" is messed up and sometimes the lights will come up when only the parking lights are turned on.
(at least not over this one).
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From: Louisville KY
$13.00 for the plastic gear at Advance Auto Parts. Dorman Part # 42400. I went with the plastic one cause the last one lasted 13 years. Some recommend the brass gear but it's heavier and cost three times as much.
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St. Jude Donor '05, '12-'13, '15-'16, '21
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Sure the brass one will never go out but the plastic one was way cheaper and will probably last another 60-70k like my last one. At 140k if i even still have the car I dought I will care about spending another 13 bucks and an hours worth of work. I bought the brass one but I should of had that mentality before I paid 50 bucks for it.
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Sure the brass one will never go out but the plastic one was way cheaper and will probably last another 60-70k like my last one. At 140k if i even still have the car I dought I will care about spending another 13 bucks and an hours worth of work. I bought the brass one but I should of had that mentality before I paid 50 bucks for it. 
It is only one of many upgrades on this car.