Have a 2005 accord 4 cylinder. When the radiator fan turns on.. my headlights dim for about a second, then back to full strength. The rad fan used to turn on and off every 20 seconds... cold or warm. Everytime the fan (looking at my rad... there are 2 fans????) turned on the lights dimmed. i had it checked out and the dealer said the accords were prone to this... but i said every 20 seconds? They checked it out and replaced the relay switch... it helped a bit. Now its only every 40 seconds the fan turns on... lights dim... fan runs for 20 seconds... shuts off.... 40 seconds later... fan on.... lights dim.... you get the picture. I have 2 other people who have the same model and year and both say there lights dont dim when the fan turns on. Wierd eh? But the dealer says this is normal. Also... when the rad fan does turn on.... you can hear and feel the vibration in the car... any help would be apprechiated.

Thanks.

also... the lights dim about half the time when the ac is turned on as well. Could it be an underpowered battery?

 

Sorry but it is normal for the lights to dim/flicker. It's common to the 7th gen. Now why you can hear the fans come on and why they do it so often is a different story.
I can certainly feel when the A/C comes on which automatically triggers the fans but the fans by themselves? Never heard or felt it inside the car.

True to Honda efficiency, the alternator and battery are no larger than they have to be to do the job.

 

should have been more specific.... i can hear and feel the ac motor at idle and driving speed. i can only hear and feel rad fans (should there be 2, and both come on and off at same time???) when im at idle. Either at idle or full highway speed... when car is warmed up , either the ac or rad fans kick in every minuite.. and this is very annoying as the lights dim to about half power ... then back up again. Allmost like the car is going into a dip in the road and the road in front looses half its light. The dealer replaced the relay switch which has changed the frequency from every 20 seconds or so to about once a minuite. This should not "be normal". If it is... this is a majour flaw in the accord and thus should be a recall. All i can do if now focus on the friggen lights and count down from 60 to 1.. then "BAM"... lights dim. Very, very frustrating.

 

well those fans are there to help keep the car cool. if you can help the car to keep cool by itself without the fans....well they wont turn on as much. the condition and molecular makeup of your coolant is one of the biggest factors in keeping your engine cool. your ecu wont even think of allowing your car to vary its temp by even a little bit.. it will run those fans every couple of seconds to make sure the water in the radiator, which will soon be in the engine....is at the perfect temp. now

-your coolant should be half water, half antifreeze. if there is more than 50 percent antifreeze in your car it will significantly diminish your cars ability to keep cool.....so maybe have your coolant changed....and not at jiffylube dammit.


-the surface tension of the water in your radiator will decide how much heat it can transfer to the metal which is then dissapated. (surface tension is the ability to overfill your glass of water and for some reason it doesnt spill over). increasing this will help your car cool better. royal purple makes a great product that you can get at your local napa, which works absolutely oustanding.


i live in az so its around 75-80 out right now. my 91 ex will idle for about 30 min before the fans come on. they just really arnt even needed unless im on it real hard (which is every damn day)

o and your car has an electrical load detector on it. the alternator doesnt make more power than it needs to.....so when the system detects strain(which is the dimming of your lights) the computer send a signal to the (IAC) intake air control valve telling it that the RPM of the motor needs to be increased slightly. the time elapsed in-between these two events is the time that you see the dimming of the lights and the shake you feel in the steering wheel. after everything is balanced you should not feel any shake...and if you do then you may have one or more bad motor mounts.