My cars check engine light came on and I did a test and it came back with the P0420 code. I went and bought DuraLube Severe Catalytic & Exhaust Treatment but I’m not sure if I should fill up the tank then add the cleaner or if I should add the cleaner with the half tank of gas in the car already.
Bad catalytic converters are typically a symptom, not the cause. Everything from vacuum leaks to exhaust manifold leaks, even misfires can cause it. You need to do more troubleshooting, or it will probably come back. I have '99 Ranger with 291k miles and the catalytic converters are the originals.
I went and bought DuraLube Severe Catalytic & Exhaust Treatment
Since there are so many things other than the catalytic converter that can trigger that code why not check some of those out first?
https://www.way.com/blog/p0420-code-what-it-is-and-how-to-fix-it/
