bad cat
yesterday had to replace the first cat converter(the one just after the manifold). the CEL came on a few months ago so I replaced the O2 sensor. 800 miles later the light came back on with the same code p0421. I am sure I will be regretting not just replacing it with a OBX header.
Lani, i had the same problem a few weeks ago. the CE light came on and when i had it checked it came up P0421- Warm up catalyst below bank 1. I was in a panic. I only had the car(01' ES 2.0) for two weeks. after looking every where for help I bought a new O2 sensor. it is the one after the first...