I have a 2001 Subaru Outback. It recently started throwing two codes, P0328 and P0420. It is also idling rough, sluggish on the highway and gas mileage is going down. I changed the plugs and wires but that does not seem to help. Whats up with the family chariot?
The first code indicates a problem with the knock sensor circuit. Make sure the connections to it are ok. There seems to be a connection problem to it somewhere.
The other code is a Catalyst System Efficiency Below Threshold (Bank 1) code error. This means the CAT isn’t working as it normally should be. The CAT itself is most likely ok but something else is causing it to show a problem. The front O2 sensor on the passenger side(bank 1) may have a problem. Before you just replace the sensor it would be wise to check the signal of that sensor to see what is happening there to help locate the trouble area. There may also be an air leak in the exhaust system after the front O2 sensor.