Headlights Dim Occasionally
Thread Starter
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Headlights Dim Occasionally
Anyone know exactly why? There was past discussions about this but I don't think anyone nailed down the exact reason why.
If I'm driving at night I see my headlights dim now and then for no apparent reason. I can also see them dim some when I hit the brakes, so I'm thinking it's due to a sudden large electrical load.
I think when the air pump comes on for emissions it must have a high startup current and also causes the light to dim for a second.
I have a good Optima battery installed, and when talk of this started years ago some guys claimed putting a better battery in the car made this phenomenon go away ... but not for me.
I'm thinking it's a lazy voltage regulator that can't make voltage regulations fast enough for sudden big current loads on the electrical system.
Any thoughts?
If I'm driving at night I see my headlights dim now and then for no apparent reason. I can also see them dim some when I hit the brakes, so I'm thinking it's due to a sudden large electrical load.
I think when the air pump comes on for emissions it must have a high startup current and also causes the light to dim for a second.
I have a good Optima battery installed, and when talk of this started years ago some guys claimed putting a better battery in the car made this phenomenon go away ... but not for me.
I'm thinking it's a lazy voltage regulator that can't make voltage regulations fast enough for sudden big current loads on the electrical system.
Any thoughts?
Last edited by ZeeOSix; Nov 7, 2007 at 02:33 AM.
Team Owner
Joined: May 2001
Posts: 36,836
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Very possible. Oh and BTW, the AIR pump only operates for a (very) few minutes after a cold startup to help light off the O2 sensors more quickly. After that it does nothing and does not run.
Le Mans Master
Joined: Feb 2002
Posts: 6,937
Likes: 21
From: Waldorf MD
Check your battery terminals, if you can rotate them by hand, they are too loose. But only torque them to 11 ft-lbs, because overtorquing is the main cause of side terminal leakage (and your computer is below the battery).
Burning Brakes
Joined: May 2007
Posts: 817
Likes: 1
From: Killeen Texas
Ive noticed this too over the past couple weeks. One evening I just happen to be in front of the car with it running and the lights on. I heard the fans kick on and noticed the lights dim at the same time. So at least thats one cause....
Former Vendor
Joined: Nov 2005
Posts: 8,995
Likes: 2
From: Spring Texas
St. Jude Donor '08
ZeeOsix: You're correct. Invision an alternator as a electrical pump. This pump is dependant on engine speed to maintain voltage "pressure".
Headlight dimming is a symptom of a voltage drop. The C5 alternator is computer controlled and only puts out the nessicary amount of power. Low voltage when stopping is common because the engine slows down (and so does the alternator) For A4 owners, It's not uncommon to see power levels drop below 13.2 volts.
Headlight dimming is a symptom of a voltage drop. The C5 alternator is computer controlled and only puts out the nessicary amount of power. Low voltage when stopping is common because the engine slows down (and so does the alternator) For A4 owners, It's not uncommon to see power levels drop below 13.2 volts.
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Thread Starter
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Also, while driving at night about 5~8 miles after startup, I can see the headlights dim for a second or two (probably 3 or 4 times during the drive) while just cruising and not operating anything electrical on the car ... so I'm assuming it's probably the AIR pump kicking in and running the emission system checks. I'll have to dig out the factory service manuals and read up on the AIR pump operation parameters.
Intermediate
Joined: Nov 2007
Posts: 46
Likes: 0
From: Baltimore Maryland
Just bought mine this weekend. Noticed the same thing on the way home. Mine dim at the top of widow travel, stepping on the breaks, or using the turn signals. Turn signals really bother me, headlights dim with each blink. Radio dims too. Has a brand new Bosch battery, so I`m confused too.
Instructor
Joined: Aug 2007
Posts: 142
Likes: 0
From: Belmont (Outside of Charlotte) NC
My lights did the same. Went away after tightening battery terminals.
Former Vendor
Joined: Nov 2005
Posts: 8,995
Likes: 2
From: Spring Texas
St. Jude Donor '08
not in use(winter) it cycles to keep it lubricated.
Tech Contributor
Joined: Dec 2006
Posts: 10,962
Likes: 29
From: Van Buren Arkansas
Wounded Warrior Escort '11
I've got the super high mileage '99 and since I work the 2nd shift, I'm leaving here at work around 11Pm each night. Two places I see the dimming happen each and every night. First is at the freeway onramp which is only two blocks away of driving and it happens again like clockwork about 10 miles away on the freeway. Part of it is loads like the air pump system and I believe the other is the charging system switching over from a higher rate charge to a lower rate to accomodate the recharge from the loss due to the engine startup. Just a guess on my part. The voltage will drop from 14.1 to 13.7 then right back up within one second. I tend to think its normal.
Advanced
Joined: Nov 2007
Posts: 82
Likes: 0
From: D'ville Tx
My car did this for a little while as well. I checked the battery conections and they were fine. I was told to check the ititial ground from the battery. It was slightly corroded. I cleaned it and the lights very rarely act up unless i get on it hard.
Thread Starter
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Racer
Joined: Mar 2006
Posts: 278
Likes: 0
From: Mississippi Gulf Coast
Mine too. Guess can check the battery terminal. To me it isn't a big deal,(yet) just happen to notice that it does do it, and was curious if it was a common thing. It seems to be.
Melting Slicks
Joined: Oct 2007
Posts: 2,798
Likes: 8
From: It's true money can't buy happiness, but it is more comfortable crying in a Corvette than on a bicyc
St. Jude Donor '13
Mine did it. Installed HID Xenons and they claim lower current draw. Well they did it. Battery is new and recently replaced. Then I read the electrical problems thread. Turned out all my ground connectors on both sides of the frame were corroded. Took them apart and cleaned everything and now I never see the lights dim.
