Piston Slap: Dimwitted Honda Accord or Dying Alternator?

Sajeev Mehta
by Sajeev Mehta

Rishi writes:

I am a long, long time lurker but not a poster on TTAC (yet). I have a question regarding a 2004 Honda Accord EX four-cylinder. When I am driving, the headlights flash at different intensities depending on what gear it is in (its an automatic). When I accelerate, and it drops some gears, the headlights flash a bit brighter, but then become dimmer as the car settles into fourth. Could this be a sign of water damage or a major electrical issue? Thanks so much for your time.

Sajeev answers:

Well, Rishi, your alternator is not especially happy at lower engine revs. From what you said, running full throttle when you need functional headlights is the way to go.

Just kidding. Charging problems come from several sources, in no particular order: corroded grounds or battery cables/terminals, a weak battery or a dying alternator. There are several voltage tools you can plug into your cigarette lighter to get real time reading of when (and to what extent) your charging system is failing, or you can go to a parts store and have their staff test the system, complimentary.

Considering your vehicle’s age and that the problem is engine speed dependent, I suspect the alternator. Have it tested, and the battery. If the alternator is burning out the (original) battery too, it might not be a bad idea to replace both at the same time.

Bonus! A Piston Slap Nugget of Wisdom:

If you have an aftermarket stereo (and like to move-it-move-it) with a big honkin’ subwoofer, that’s another problem: adding a capacitor between the battery and the amplifier usually fixes it. And it’ll reduce the parasitic drag of one seriously thirsty subsystem on your car’s charging system.

[Send you technical queries to: mehta@ttac.com]

Sajeev Mehta
Sajeev Mehta

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  • George B George B on Aug 14, 2009

    Honda TSB 05-034 sounds like the solution. Probably obvious, but do the free and cheap maintenance stuff first. Clean corrosion off the battery terminals and add distilled water to the battery as needed to bring the electrolyte up to the correct level. The Delphi alternator in my 99 Accord failed at 45k miles. I complained to American Honda and they discounted the replacement cost even though it was out of warranty. The dealer service department said they had seen several failures for the Delphi alternator and none for similar Accords with the Denso alternator.

  • Patrickj Patrickj on Aug 14, 2009

    @Orangutan That would make it a Euro Accord with a Maryland license plate...

  • Golden2husky Golden2husky on Aug 14, 2009

    Most Mopars of the mid 80's through the 90's used a voltage regulator that was integrated into the power control module under the hood by the battery. It provided the power control and operation of the commands that originated in the logic control module that was inside the car by the passenger footwell. In later models, the two units were combined into one. Don't really why they were built that way, maybe to save money?

  • Wheeljack Wheeljack on Aug 15, 2009

    A 2004 car (and a Japanese one, no less) with an alternator problem already? Seriously? My old (1976) Ford truck had the original alternator on it when I sold it a few years back with a mere 188,000 miles on it. Oh wait, that can't possibly be right since all American cars are junk...or at least that's what I hear on the internet.