# Headlights Dim When Gas Pedal Released -- Battery Ready to Fail?
**URL:** https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298
**Category:** Factual Questions
**Created:** [December 8, 2006, 2:22am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298 "2006-12-08T02:22:19Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@fessie](https://boards.straightdope.com/u/fessie)
#### Post date: [December 8, 2006, 2:22am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/1 "2006-12-08T02:22:19Z")
Pretty much just that question - we’ve got a 2004 Accord, bought it in Chicago w/7k miles on it, now it has 45k. I’ve noticed the headlights dim a little when I release the gas pedal. It’s just a little slow to turn over when I start it in this cold weather, but I haven’t had to do any “pumping” (it’s in our garage overnight). Time for a new battery?
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### Author:  [@bouv](https://boards.straightdope.com/u/bouv)
#### Post date: [December 8, 2006, 2:24am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/2 "2006-12-08T02:24:38Z")
Actually, I think that might be the alternator. Once the car’s running, it shouldn’t be relying on the battery for power.
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### Author:  [@fessie](https://boards.straightdope.com/u/fessie)
#### Post date: [December 8, 2006, 2:28am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/3 "2006-12-08T02:28:36Z")
Aww, crap, those cost more, don’t they…hmmm…better check that warranty (yes, dh purchased an Extended Warranty on our Honda, don’t laugh).
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### Author:  [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)
#### Post date: [December 8, 2006, 2:29am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/4 "2006-12-08T02:29:29Z")
[QUOTE=fessie]
Pretty much just that question - we’ve got a 2004 Accord, bought it in Chicago w/7k miles on it, now it has 45k. I’ve noticed the headlights dim a little when I release the gas pedal. It’s just a little slow to turn over when I start it in this cold weather, but I haven’t had to do any “pumping” (it’s in our garage overnight). Time for a new battery?
[/QUOTE]
It sounds like a failing alternator and/or a bad ground. I’d get it checked out quick (either should be easily diagnosed by a competent mechanic) if you don’t want to find yourself stranded somewhere.
In my experience, modern sealed car batteries give little to no warning when they go; you just walk out one day, try to start her up, and she’s dead. The last battery lasted nearly seven years and ~200k miles; I’d be majorly pissed to have a battery die at 45k.
Stranger
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### Author:  [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)
#### Post date: [December 8, 2006, 3:02am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/5 "2006-12-08T03:02:42Z")
The battery is likely going bad.
It may however be ok and the conection is just corroded and in need of cleaning.
The alternator is a possibility, but not what I would rate as the most likely cause.
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### Author:  [@Rysdad](https://boards.straightdope.com/u/Rysdad)
#### Post date: [December 8, 2006, 3:07am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/6 "2006-12-08T03:07:04Z")
Another vote for alternator. At least they’re an easy fix.
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### Author:  [@simster](https://boards.straightdope.com/u/simster)
#### Post date: [December 8, 2006, 3:40am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/7 "2006-12-08T03:40:31Z")
another note to get the alternater checked out… a quality autoparts store should be able to test both and tell you definitively which it is.
Catch a bad alternator in time, save your battery… let it go long enough and you;ll be buying both.
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### Author:  [@fessie](https://boards.straightdope.com/u/fessie)
#### Post date: [December 8, 2006, 3:53am UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/8 "2006-12-08T03:53:47Z")
Thanks for the votes! I’ll call the dealership in the morning, that warranty’s got to be around here somewhere.
I’m supposed to take a trip out of town with my almost-3-yr-olds tomorrow - that poor family in Oregon has really been on my mind. No way can I hit the road w/my car’s performance in any doubt!
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### Author:  [@Frank](https://boards.straightdope.com/u/Frank)
#### Post date: [December 8, 2006, 1:56pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/9 "2006-12-08T13:56:22Z")
Though it appears the question has been answered, I’ll move this anyway.
Moved from IMHO to GQ.
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [December 8, 2006, 2:03pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/10 "2006-12-08T14:03:20Z")
I have a '99 Jeep Cherokee. Its headlights have dimmed slightly whenever the cooling fan comes on. It’s done this since new, and I have had no charging problems.
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### Author:  [@simster](https://boards.straightdope.com/u/simster)
#### Post date: [December 8, 2006, 2:09pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/11 "2006-12-08T14:09:15Z")
[QUOTE=Johnny L.A.]
I have a '99 Jeep Cherokee. Its headlights have dimmed slightly whenever the cooling fan comes on. It’s done this since new, and I have had no charging problems.
[/QUOTE]
but it’s only momentary, right? thats due to the initial load that big honkin fan puts on the system on start…
(used to have a 99 as well).
OP is implying that they stay dim until she speeds up the idle… classic sign that something is wrong in the charging system. (at idle, the alternator isn’t supplying enough amps)
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [December 8, 2006, 2:10pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/12 "2006-12-08T14:10:14Z")
[QUOTE=simster]
but it’s only momentary, right? thats due to the initial load that big honkin fan puts on the system on start…
[/QUOTE]
That is correct.
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### Author:  [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)
#### Post date: [December 8, 2006, 2:32pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/13 "2006-12-08T14:32:37Z")
[QUOTE=Harmonious Discord]
The battery is likely going bad.
It may however be ok and the conection is just corroded and in need of cleaning.
The alternator is a possibility, but not what I would rate as the most likely cause.
[/QUOTE]
Why? The battery provides power to start the car. Once the engine’s running, the battery is being charged rather than tapped for energy. If there is a power loss when the engine is running, power from the alternator isn’t getting to where it’s supposed to go, either because the alternator itself is bad or some other glitch in the connections.
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [December 8, 2006, 2:33pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/14 "2006-12-08T14:33:24Z")
A loose ground to the headlights, or corrosion in the connector that feed the headlights could also cause these symptoms. Car is from Chicago. IIRC Chicago uses salt in the winter. Salt causes corrosion.
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### Author:  [@fessie](https://boards.straightdope.com/u/fessie)
#### Post date: [December 8, 2006, 5:02pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/15 "2006-12-08T17:02:36Z")
Well, I just got back from the Honda dealer - the Service Consultant told me right off the bat that a little bit of dimming is perfectly normal. He ran diagnostics anyway, took about 10 minutes (enough time for me to have one of their donuts - yum!). Yep, he says, nothing’s wrong.
I hope he’s being honest w/me - we recently moved here and I haven’t taken the car to them before, but the other Honda dealers I’ve worked with in the past have been outstanding.
We also never lived out in the boonies before. It is absolutely pitch dark where I drive. Is it possible that, as a suburban dweller, I just never noticed it before b/c of the streetlights?
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### Author:  [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)
#### Post date: [December 8, 2006, 5:15pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/16 "2006-12-08T17:15:26Z")
[QUOTE=fessie]
We also never lived out in the boonies before. It is absolutely pitch dark where I drive. Is it possible that, as a suburban dweller, I just never noticed it before b/c of the streetlights?
[/QUOTE]
That’s definitely possible, and if your mechanic says it’s normal, well, he’s the authority. That seems kind of…weak, though. Even the crappy GM products I’ve driven (Chevy Corsica, Pontiac 6000) with their regular alternator failures didn’t perceivably dim whenever the car was at idle.
Stranger
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### Author:  [@According\_to\_Pliny](https://boards.straightdope.com/u/According_to_Pliny)
#### Post date: [December 8, 2006, 5:21pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/17 "2006-12-08T17:21:50Z")
I had a problem like that but the battery was fine.
The problem was a wire that had come loose from its binder strap and was scuffing back and forth across the wheel shroud as I drove. It therefore got a bare spot. When the bare spot glanced over the metal the wire would short out.
You couldn’t see the break on the insulation because it was on the wheel side, but you could feel it.
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### Author:  [@Leaffan](https://boards.straightdope.com/u/Leaffan)
#### Post date: [December 8, 2006, 5:35pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/18 "2006-12-08T17:35:44Z")
I had a Honda CRX that behaved exactly as you said: the lights dimmed when I stopped. The alternator finally failed after about a year of this, with one week left on my 5 year warranty.
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### Author:  [@fessie](https://boards.straightdope.com/u/fessie)
#### Post date: [December 8, 2006, 5:51pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/19 "2006-12-08T17:51:39Z")
Ahh Ahhh – my parents had a 1985 CRX! I loved that car, only decent automobile they ever bought & they let me drive it all the time (I was in college)! Forty-five mpg!
Wish they still made 'em.
Not that I could stick 2 carseats in one, but still…
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### Author:  [@Starving\_Artist](https://boards.straightdope.com/u/Starving_Artist)
#### Post date: [December 8, 2006, 6:28pm UTC](https://boards.straightdope.com/t/headlights-dim-when-gas-pedal-released-battery-ready-to-fail/383298/20 "2006-12-08T18:28:31Z")
I’d suggest a second opinion, **fessie**. I just did a Google search and found lots of hits regarding people with lights that dimmed but I found nothing to indicate that this is normal and I’ve never had a car in which dimming lights was considered normal.
I’d definitely get it checked out further before going on a trip.
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