Is it harmful to put power steering fluid in a Tacoma power steering systems that calls for ATF?

If you bought generic Power steering fluid, it must say on the bottle 'Suitable for Toyota"..even if it says 'suitable for ALL vehicles' that's not good enough. It will probably not do any harm, but the keyword is probably, and really should have Toyota ATF, taking no chances. Personally I would be uncomfortable with anything else in my Toyota

we only put a quarter of an once to top off the unit before we noticed, think this would cause any harm?

Probably that small of an amount won't hurt a thing, but FordNut is correct, only use what is specified for your vehicle. Using the wrong fluid in some vehicles can be a really expensive repair.

Thank you both very much, will have to determine why I have lost some fluid this weekend. Understand it is a 2001 and has 226,000 miles with no major problems as yet. knock on wood!

Fluid loss = leak. Find the leak and fix it. Best of luck to you.