That depends on the electronic ignition system. Read the manufacturer's recommendations in the owners manual. Most GM vehicles are now suggesting 100,000 miles on a set of plugs.
I called Toyota Canada and they told me they are lifetime spark plugs which never need to be changed. However, no matter what kind of plugs they put in the engine from day one are never lifetime. I have 110,000kms on my van right now and I am going to change them. I am starting to see a decrease in fuel milage so I guess that's when you should think about changing them out. Might not be the problem but never hurts to change them out. I am going to go with a really high end spark plug the NGK Laser Iridium plug which will last me over 100,000km's.
Follow the plug wires and find the plugs. Sometimes the plugs can be hard to get out.
The 2001 Toyota Sienna spark plug gap is .023. Most spark plugs will be pre-gapped by the manufacture of the spark plug.
I just spoke with a Parts person at a local Toyota dealer. He told me that the 2004 Toyota Matrix requires Iridium spark plugs, which retails for about $12 at the dealership, and it should not need to be changed until 120,000 miles.
Same relative position as the front plugs. They are just a lot harder to reach.
Good and tight, but don't break the thing.
Toyota says to change at 30,000 mile intervals in order to maintain Emissions warranty.
every 200,000 miles
Try to use Toyota speaker adapter plugs so you don't need to cut wires and mess the electric system up. You can get them from Ebay or Amazon.
It is feeling silly and my other answer is it is behaving badly
100K if they are platinum plugs, 50K if they are regular plugs.
every 100,000 km