1998 P0420 Code
 

My OBD2 code reader is telling me that I have a Catalyst System Efficiency Below Threshold (Bank 1).

Which side is Bank 1? Driver or passenger?

While searching on the internet I found the following:

*Leaded fuel was used where unleaded was called for
*A damaged or failed oxygen sensor (HO2S) Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
*The engine coolant temperature sensor is not working properly
*Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
*Retarded spark timing
*The oxygen sensors in front and behind the converter are reporting too similar of readings
*Leaking fuel injector or high fuel pressure
*Cylinder misfire
*Oil contamination

I know for sure my coolant temp sensor is not working but the electric fan turns on and off. Must be a separate temp switch!?

I checked for an exhaust leak by tightening the bolts on the exhaust manifold and found a broken one on the driver side closest to the firewall. On the same side, I also noticed a small oil leak coming from a plugged port on the head just above the exhaust manifold flange. It is dripping right onto the flange.

Looks like I found the Trifecta of problems....if Bank 1 is the Driverside.

Any help would be appreciated