I don't think you will ever find out because the pressure washer has a plug with 2, or maybe 3, prongs that fit into a standard electrical 110 volt A/C (alternating current) outlet. Your car has a 12 volt D/C (direct current) power supply and the outlets, formerly called cigarette lighters, are round and incapable of accepting the plug from the pressure washer.
What is the current draw of the equipment you will use in your car? Typical small appliances can be used with most inverters. If you'll be using heavy-draw equipment like some large power tools or large TVs (over 13"), then you'll need a larger-capacity inverter and a direct connection to the battery. Best check your owner's manual or check with Toyota dealer. Safety issues should be no different than using anything electric around water-be careful. Does the power washer have a three prong outlet-suggesting that the mfg wanted users to plug it into a ground fault outlet, something not possible on a car.
Most of the built-in automobile inverters I'm familiar with have a given maximum capacity rated at "100 watts". Why they rated them in watts , I don't know. This means you can use a 100 watt light bulb plugged into that connection. I've seen hair dryers, electric shavers, and computers plugged into these. I have seen some laptop computer draw too much current for charging from these auto 110v. outlet's too work. I don't have my charts handy at this moment but you, or someone, may can do the conversion from watts to amps for this. BUT, I'm dead sure you cannot use an electric pressure washer from your auto's 110v. electrical outlet. The motor on your pressure washer will draw too many amps for this. On the other hand-I have seen one situation where a customer bought a 5000 watt inverter and wondered why his battery kept going dead. The truck's charging system could not keep up with it's own electrical needs and his added load. My 2¢ worth, David
The Matrix alternator is rated 80A (12v), so you've got 960w max continuous, but of course a ton of that is used by the engine itself. A 12 amp pressure washer is going to pull 1320w continuous, so even before you worry about the inverter spec (and Thurman is correct, it's 100w) the answer is no.
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