I have a 1996 Explorer and the Check Engine Light has been coming on.
I took it to Autozone for a scan and they got CODE P0420 which is "Catalyst system efficency below threshold (Bank 1)" Can anyone please shed some light on this and give some idea as to what the problem is. Thanks.

 

Here's what I know. Your Explorer has an oxygen sensor after the catalyst to monitor the condition of the catalyst. (There's also one before the catalyst to provide feedback for fuel control.) So, either the catalyst is bad or the O2 sensor is bad and giving false information to the computer. There may be something else that is wrong that could give the same code, but I'm not aware of it. You should try to get your hands on the factory service emissions manual if you want to do this yourself. Try your local library.

 

Ok if it was a O2 sensor it would give you a upstream or down stream but this code gives you a catlist code so this means that the converter is not doing it's job it needs to be replaced. O2 sensors are good.

 

You never got back to me on the last question I asked you about the plugs & wires you installed .

 

Paul,
I have not found out what brand of plugs and wires my mechanic used when he did the tune-up, he has beeen off this week. Another thing I should note is I have noticed a considerable amount of water dripping from the tail pipe in the morning. I climbed under the vehicle and also noticed water dripping down from the catalytic converter shroud. I checked the coolant level and it is ok. Checked the oil dipstick and no evidence of milk in there and not alot of white smoke from tail pipe. The water that is dripping seems to be pretty clear. After a few miles there is no evidence of water dripping. I have had blown head gaskets in other vehicles in the past so I dont think thats what it is but not entirely sure, I HOPE NOT. Maybe this futher info. can help you with my CEL diagnosis.
Thanks Paul,

 

Kevin , If you live in a cold climate then what you are seeing is condenstaion , I wouldnt worry about that too much . All you have to do is remove the easiest spark plug to get to & see what brand it is . The reason I suggested this is because that engine seems very fussy about what spark plugs are used in it . Even though you may not notice it the various sensors that monitor the engine can detect a slight misfire & set the PO420 Code . I know a lot of newer vehicle mufflers have small holes to drain condenstaion , But I dont think the converter should have any drain holes . Thats another thing that can set PO420 is any damage , cracks , holes , leaks etc in the Cat Conv.

 

You are right on the plugs being a factor on drivability but i have never had a code set for the catlist because of the plugs when you have a plug misfire it will set a misfire code. i would not use anyother plug than a platinum or dubble plat. plug . then you won't have to worry about them for another 100,000 miles