Mechanics

DOOR AJAR, TRUCK AJAR, BRAKE LIGHT BULB WARNING LIGHTS FLICKER ON ACCELERATION

1998 Honda Accord • 180,000 miles

When the car is cold upon accelerating these warning lights on the dash flicker. If I let off the gas they stop. Once the car is warmed up, they will flicker only on high acceleration. Note that the battery and/or brake light do not come on it's only the warning lights on the picture on the car on the bottom of the Fuel and Temp cluster. Just recently replaced the alternator since the original failed. Checked voltage and it's charging correctly. Car not driving weird in any way these just flicker for some reason. Should I be concerned? What might this be?
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Renn
October 14, 2013.



Voltage readings only tell part of the story about the charging system. If you find the battery voltage is between 13.75 and 14.75 volts with the engine running, you know the generator is doing something, but that's all. It also has to be professionally load-tested for maximum output current and "ripple" voltage.

There's six diodes in the generator. If one fails, you will lose exactly two thirds of the generator's maximum output current. That leaves you with not enough current to run the entire electrical system under all conditions. The battery will have to make up the difference.

With a bad diode, you lose one phase of the three-phase output. During the periods of the missing phase, voltage drops significantly. That variation in output voltage is the ripple voltage. That goes very high. That can affect computers and confuse them so weird things can happen. Most often people notice that as dash warning lights turning on for no apparent reason.

A totally unrelated cause of intermittent dash lights has to do with something rubbing and shorting inside the generator and that can occur at higher engine speeds when there's more centrifugal force acting on the rotor. That is harder to detect and it won't show up with a load-test.

A point to keep in mind is that due to how the voltage regulators work, AC generators, ("alternator" is copyrighted by Chrysler), can produce voltage spikes. GM has a huge problem with this. I haven't really heard of it being a problem on any other brands, but the battery is the key component in absorbing and dampening those harmful spikes. To prevent repeat generator failures, if you have them, replace the battery at the same time unless it is less than about two years old.

Caradiodoc
Oct 14, 2013.
Thanks for the info. Just out of curiosity even though the battery light nor the brake light flash or flicker that would still be an Alternator issue? I know that when the alternator went out all those light came on. Thanks again.

Tiny
Renn
Oct 14, 2013.
Sorry to ignore you for so long. I just accidentally found a bunch of automated e-mails in my spam folder.

By the '98 models the engineers had already hung a computer onto every system in our cars that never needed computers before. They are very intolerant of low voltage and voltage fluctuations. When a diode in the generator fails you lose two thirds of its current output, and during the time that missing phase is supposed to be there, the output voltage, (electrical pressure) drops. That's that ripple voltage I mentioned. That is what confuses computers, then they may shut down, and turn on their warning light to tell you, or the fluctuating voltage can interfere with a computer's sensor readings and cause it to do incorrect things.

With a bad diode, you will still find the correct system voltage of between 13.75 and 14.75 volts, and it might even be a little high, (which is a clue), due to the voltage regulator responding to those dips in the ripple voltage. Just like an air compressor, the generator can only maintain the desired voltage as long as you aren't drawing too much current. Once the requested volume, in air from the compressor, or current from the generator, exceeds the units' capacity, air pressure, or electrical pressure, (voltage), will drop. That's when computers start to do weird things.

The only way to diagnose a failed diode is with a professional load test on the charging system. That takes all of five seconds. It takes longer to wheel the tester to the car and hook up the cables.

Caradiodoc
Nov 4, 2013.