Legal Question in Product Liability in Colorado

The first thing you can do is report the incident to the government agency that collects this kind of data (NHTSA): https://www-odi.nhtsa.dot.gov/ivoq/. If you and others complain about the same problem, it could lead to action by the government.

The second thing I would recommend is talking to your dealer where the repair was done. If in fact the plug failed after only 18 months, they may voluntarily take responsibility for it and fix your vehicle. If they refuse, you should consider talking to an independent repair person and having him/her document what happened. If you can find someone to testify that the plug was defective in design or manufacture, you can bring a lawsuit against the dealership and/or Toyota to repair you engine. You'll also probably want to find and talk to a consumers rights lawyer in your area if it looks like Toyota won't fix thre problem voluntarily.