Honda Car Forum

Bizarre, however while driving, my headlights will fade in
and out by 50% every 2-5 minutes. Its not caused by road
terrain. Any thoughts?

In article <fvv7q1l360rpec06gltkuttpqc2lr9sr3t@4ax.com>,
Fred@wonderful.com says...
> Bizarre, however while driving, my headlights will fade in
> and out by 50% every 2-5 minutes. Its not caused by road
> terrain. Any thoughts?

It's caused by the air conditioner compressor cycling in.
When you use the windshield defroster, by default the A/C runs also, to
dehumidify the air.

There is even has an explanation for it:

Headlights & Dash Lights Dim With Electrical Load

NOTE: This article applies to all Honda models
except Passport.
Soon after the change from daylight savings time to
standard time (the last Sunday in October), Tech Line
gets numerous calls about flickering or dimming
headlights and/or dash lights when the brakes or turn
signals are used.
This flickering or dimming happens when the battery
is supplying most of the current for the electrical load
instead of the alternator (something a customer is
more likely to notice when their headlights are turned
on).
Since the early ’90s, Honda vehicles have come with
an electrical load detector (ELD) unit in the
under-hood fuse/relay box. This unit allows the
ECM/PCM to regulate the alternator (switch it
between high output and low output) to provide the
best combination of fuel economy and electrical
system operation. The ELD sends a signal to the
ECM/PCM that’s proportional to the electrical
demand. The ECM/PCM switches the alternator
between high output and low output depending on
several factors, which include electrical demand,
battery charge level, and the driving cycle. When the
alternator is in low output, the engine load is reduced
and fuel economy improves.
If your customer complains about this flickering or
dimming, tell them about the ELD unit and how it
works. Unless the engine won’t crank, or the vehicle
has other symptoms of a weak battery, chances are the
flickering or dimming isn’t an electrical problem.

--Gene

On Sat, 17 Dec 2005 10:16:03 -0500, Gene S. Berkowitz
<first.last@comcast.net> wrote:

>In article <fvv7q1l360rpec06gltkuttpqc2lr9sr3t@4ax.com>,
>Fred@wonderful.com says...
>> Bizarre, however while driving, my headlights will fade in
>> and out by 50% every 2-5 minutes. Its not caused by road
>> terrain. Any thoughts?
>
>It's caused by the air conditioner compressor cycling in.
>When you use the windshield defroster, by default the A/C runs also, to
>dehumidify the air.
>
>There is even has an explanation for it:
>
>Headlights & Dash Lights Dim With Electrical Load
>
>NOTE: This article applies to all Honda models
>except Passport.
>Soon after the change from daylight savings time to
>standard time (the last Sunday in October), Tech Line
>gets numerous calls about flickering or dimming
>headlights and/or dash lights when the brakes or turn
>signals are used.
>This flickering or dimming happens when the battery
>is supplying most of the current for the electrical load
>instead of the alternator (something a customer is
>more likely to notice when their headlights are turned
>on).
>Since the early ’90s, Honda vehicles have come with
>an electrical load detector (ELD) unit in the
>under-hood fuse/relay box. This unit allows the
>ECM/PCM to regulate the alternator (switch it
>between high output and low output) to provide the
>best combination of fuel economy and electrical
>system operation. The ELD sends a signal to the
>ECM/PCM that’s proportional to the electrical
>demand. The ECM/PCM switches the alternator
>between high output and low output depending on
>several factors, which include electrical demand,
>battery charge level, and the driving cycle. When the
>alternator is in low output, the engine load is reduced
>and fuel economy improves.
>If your customer complains about this flickering or
>dimming, tell them about the ELD unit and how it
>works. Unless the engine won’t crank, or the vehicle
>has other symptoms of a weak battery, chances are the
>flickering or dimming isn’t an electrical problem.
>
>--Gene
Thanks Gene, however it continues with the climate control
off as well.