After reading through some really impressive posts, I thought I'd sign up to see if someone was able to help.

The situation: Steady-running 2007 Fit Sport, 159,000 miles.

1. Upon cold start, runs fine. However, the electrical system will erratically drop out for less than a second. Radio goes off, guages drop to zero, steering becomes stiff. Some warning indicators light including Electric Power Steering indicator. Engine does not stall. Within a second or less, electricity returns to normal and car functions normally. This can happen as frequently as once per minute or more erratically every few minutes or so.
2. When car is warmed up, dropouts stop.
3. Happens only when temperature is close to freezing temperature.
4. Happens erratically. Sometimes, even when cold, things run fine.

Because this is erratic, it's hard to get diagnosed by bringing it to a mechanic. Could someone provide guidance about what might be causing this?

Thanks in advance!

 

Check the battery terminals. I know on my hondas they tend to stretch and cause a bad connection. If not that it may be a loose fuse, bad ignition switch, bad ground somewhere. The possibilities are pretty wide and with it being intermittent you would have to have a good mechanic to find it. You can try wiggling things to see if you can get it to act up like the fuse boxes, ignition switch, wiring harnesses. This may help you localize it. You should probably get a power and ground distribution diagram.

You should probably get a code scan as that might point you in the right direction there may be codes stored in modules telling you that they lost communications etc. that may not trip an engine light

My wiring diagram search shows that
Fuse 3 (50A) underhood goes through the ignition switch and powers a lot including these three systems
check this fuse for fitment and condition.
I could not find any other fuses that power all three system but they may share connectors.

My first guess would probably be the ignition switch

 

battery to body ground wire
alternator fuse, mentioned above
alternator (brushes)

 

Thank you @tyrtill! I appreciate the thoroughness of your response. You've given me a lot to go on! Especially appreciate your identifying Fuse 3 as a possible link. I'll post more as this mystery gets solved.

 

Thank you @doctor J! I'll start with these, see what comes up. Appreciate your input, and I'll let you know what I find out!

 

Yesterday, it was chilly and wet, around forty degrees. Drove a few minutes to the grocery, parked, shut off the car. I noticed the key fob did not lock the doors, and upon checking, neither did the door lock switch inside. Put the key in the ignition and tried to start, and got absolutely no response at all. No lights, no starter, no nothing. Dead.

Called a tow company, but had to wait about two hours for the truck to arrive. For the hell of it, when the truck arrived I tried starting and it started right up. Damn! Drove a few miles to the repair shop. Along the way, frequent electrical dropouts, fraction of a second. Dash went dead for just a flash, during which the airbag warning light came on before everything returned to normal.

By the time I arrived at the shop, the dropouts were happening less frequently, perhaps because the car was warming up. When the mechanic tested it a little later, everything seemed fine.

I've given him the suggestions from @tyrtill and @doctor J - hoping we can get this figured out. Any other suggestions based on this new data would be gratefully received!

 

Really sounds like a bad battery connection or main battery ground

 

Thanks @tyrtill - they looked pretty solid when I checked the other day, but I'll have the mechanic take another look.

 

Quick update: The mechanic went through the list you all provided. Everything checked out with the possible exception of the alternator. We went ahead and replaced the alternator.

The car is running fine at the moment. I'll update once I'm confident the problem is fixed, or if it turns out there's still something weird going on, either way.

 

Update: All good. We haven't had a cold snap near or below freezing to fully test it, but so far things are running well. Replacing the alternator seems to have done the trick.