My girlfriend's 2002 Accord most likely has some cracked ceramic material inside. It rattles occasionally. She took it to my mechanic just to have a look and get a quote, and they told her the cat does need to be replaced.

I can do it myself if rust hasn't welded the bolts, but we're trying to avoid the $500-700 OEM part. Has anyone replaced a catalytic converter with an aftermarket brand that fit correctly and didn't throw a check engine light? Or do we just have to give in and buy the expensive OEM Honda cat?

 

If you plan to change out the cat yourself, pay attention to the "Test Group Name" on this application chart.

https://ssl.arb.ca.gov/PartsSearchTo...earchTool.aspx

The Accords with the ULEV engine will require a cat that has more catalyst cells than those that are not ULEV. Getting the wrong cat will throw the same P0420 code. All these cat listed in the application guide is all CA legal parts.