My wife's check engine light has been on in her 1997 4 door Explorer 4x4 with the 4.0 liter SOHC, automatic. I had checked it at Auto Zone several months ago and I thought that it only gave one code for the downstream O2 sensors, when I went back yesterday it gave the codes for both downstream sensors P0420 & P0430. It seems really odd, to me, that both would have gone at around the same time and I would like to exhaust all the troubleshooting options before I spend the $100 or so for two sensors that may not solve the problem. I would appreciate any ideas that could rule out any other possible causes.

Thanks,
Randy

 

I forgot to mention that the car is running good. I have not figured out the gas mileage, but compared to our other Explorer it does not seem out of line. I replaced the plugs and wires about a year ago.

Thanks,
Randy