Was fixing some minor underbody curb damage to my 2009 Honda Fit, and found a power cable that terminates in a male US 120V AC plug, on the passenger side, complete with a protective rubber hood.

Could not find this on wiring diagrams.

Does anyone know what this is for?

 

Probably the optional block heater.

 

Engine block heater. Honda dealers do offer them. A popular accessory back east and up in Canada.

 

for a little ol' honda fit. would never have guessed. I suppose one of those could be handy here in northern new mexico where winter nights routinely drop into the 0..10F range, but haven't needed one so far.

thanks very much for the clarification.

 

It's really intended for when the temperatures go down to the -20 or -30 range. When I was young I used to use the block heater every night so that my car would start in the morning. That was in the good old days when cars had carburetors and the like. Nowadays with electronic ignition, fuel injection, ultra thin oil and computerized everything I haven't plugged in a block heater in a couple of decades. Even with that pukie little OEM battery the Fit starts up on it's own at any temperature. In a holdover from the old days I believe that block heaters are still mandatory and must be installed by new car dealers in my province which is why my Fit has one,

 

A block heater will heat up the oil, coolant and engine. Car will become hot inside faster. Will also reach operating temp faster, and pollute less at the same time.
Even with 0W20 synthetic oil, the oil can get pretty thick at -20 °F. So at the end, it helps protect the engine in cold climates.

I use mine (sadly not on the Fit, but on my other car) every time it gets around 32 °F during the night.

 

Actually the block heater does not heat up the oil which is sitting in the oil pan well below the engine. It will heat up whatever residual oil is still coating engine block parts which momentarily helps with the initial start up. Once upon a time I had a dipstick heater which replaced the original dipstick in my old car. It had a built in electric heater and also plugged into a wall outlet. Did a great job heating up all the oil in the oil pan. And I had a block heater and an electric battery blanket heater** and an interior heater to warm up the interior of the car.

**I still have one which I used on the Fit OEM battery for a few years. When I upgraded to the larger battery it would no longer fit around it and so it now sits in my basement somewhere.

 

It for sure heats the oil and coolant. Clearly if the block is warming so is everything inside of it.

https://www.minit-tune.com/blog/ever...-block-heaters

"A block heater helps keep your car engine warm while you’re not driving it. Once it gets plugged into a regular 110-volt outlet, the heater warms the engine block as well as internal fluids like the oil and coolant.

Cold temperatures make engine fluids sticky and viscous, which can make it more difficult to start a car. In extreme temperatures, your engine may not start at all. Warming the motor before you turn the ignition prevents wear and tear on your vehicle. It also has the benefit of getting hot air through your vents more quickly to warm you up inside."