Originally posted by litljenarey:
I searched, I know what the code is for. I know that it's cats for some people, O2 sensors for other people, and some people just erase the code and it never comes back....Why would it only happen when the heat is on??
Ford won't help me, I have 99K miles. I just bought the car last week, so I don't know much about them. Any suggestions on how to find out if that's really the problem?



Wait I see you added to your signature you have a Zetec.

Well then that just about eliminates the cat. therory, that mainly applies to V6s.

I would honesty take it to a shop because PO420 can be caused by about 12 different things. They have a scan tool that will say what sensor or whatever the problem is that isnt working how it should.

Anyways O2 sensor, MAF I've heard are the two I would start with if you want to toss parts at it. The MAF can be cleaned while the O2 sensor is about $80.

hope that helps