Unusual voltage at startup

[YouBetcha]

I've looked up and down for anything similar to this issue. Dealer has observed the issue but could not identify a cause. Car is a 2000 XLE V6 (1MZ-FE) about 100K miles.

For the first 3-4 minutes after a cold startup, my car's voltage rises and falls at a very consistent rate of about twice a second. Then, all at once, it smooths out (no transition between the fluctuations and "smooth" voltage). It does not seem like a loose ground/connection issue, because the fluctuation is so perfectly consistent, and I've looked at and jiggled everything searching for a loose connection. At it quits exactly the same way each time. Also, it doesn't matter what RPM the engine is running at, if the car is moving or parked, etc. It is always the same.

So, this car is like a UFO calling home for 4 minutes in the morning, because the headlights, interior lights, dash, all pulse at the very consistent 2 hz rate (not completely on and off, more of a brief flicker).

I have changed the battery and alternator (with a refurbished Denso alternator) but neither stopped the "flickering."

My only guess (based on what could possibly be turning on and off at startup) is that the car has CA emissions, could it just be the A/F sensors drawing a ton of power at startup? Add this to the cold northeast (we are really far away from CA) and lights on in the morning -- could it just be too much draw on the alternator? If that is it, I guess I'm not too worried about it but it is still annoying.

[toyomoho]

Use a voltmeter to check for these same fluxation at the battery. If so start checking the cables and connections for the battery and alternator, it is possible there is a bad connection somewhere.

The alternator should put out at least 80 amps; thought the 02 sensor heaters were always on. Take a notice of anything that cycles on/off in time with the voltage variation. Most cars have a cold start fuel injector system that stops after a few minutes of running. Start pulling fuses on circuits that are not needed to run the engine and see if the voltage stabilizes.

If for some reason you end up tripping the check engine light it can be reset by removing the EFI fuse.

[parimento1]

most likely a bad voltage regulator, there are threads about this if I remember on the Avalon forum.

[dc_98_cam]

Do you understand the basics about cleaning battery terminals .. and the alternator connections? The battery post surfaces must be bright and shiny ... use a small fine wire brush for this. Also, the interior contact surfaces of the battery cable clamps must be bright and shiny.

See if you can follow the positive and negative battery cable to their opposite ends ... remove bolts, clean thoroughly, and replace. It is usually a good idea to buy a can of spray type electrical contact cleaner from your electronics store ... Use this liberally on any terminal, clamp, and plugs before you reconnect them ... It gets rid of non-conducting grease or dirt.

Try measuring the voltage at the battery in the morning .... maybe turn off headlights and heater to see if that makes a difference.

For safety and damage avoidance ... always remove the negative battery cable first, and when you are ready to start the engine, reinstall the negative battery cable.