Mazda Repair: 1999 Coil Pack, o2 sensors, coil pack

Question
Hi,
Me again.... I replaced the coil pack and picked up the little car today.  At mile 5 - the CIL came on.  I had it read and it is a code P0420.  

What do you think - is the cat gone now because of the coilpack?  What is the cost of getting that replaced.  

I'm thinking of just driving this down to NO so you can play with it.  If you weren't 8 hours away that is!!!

Thanks for your advice.

Leigha


Answer
That code is a converter efficiency fault.  The most common failure is an oxygen sensor.  My first course of repair would be to have the surface areas of both O2 sensors cleaned.  Since a misfire was happening partial combustion could have fouled one or both and a misread is possible.  Have the MIL reset.   If it is a failure is will indicate it by MIL after two drive cycles.

The O2 sensors are read by the computer which is very picky and any out of perimeter calculations set off a fault, even small variations.

You have low mileage if I recall, converters even in low use older Miatas should see 80k+ so not likely a converter problem.