I'll give you a start as the code definitions I'm using are for a '97 - SOMEONE correct me if I'm wrong!
136 Oxygen sensor - DTC P0136 and P0156 indicate the output voltage of the downstream HO2S is less than some calibratable functional window.
141 Oxygen sensor - Diagnostic Trouble Codes (DTCs) P0135, P0141, P0155 and P0161 indicate a short to ground, open, or short to VPWR in the HO2S heater circuit.
304 Misfire - Misfire Continuous Memory Diagnostic Trouble Codes (DTCs):P0304 - Cyl No.4, Fuel Inj.
So the first two relate directly to the O2 sensor
1)inspect the connections on/to the downstream O2 sensor - spray the plug in connectors with electrical cleaner(DO NOT CLEAN THE O2 sensor)a dab of silicone grease on the connectors. Look for burnt/squashed wires - cheap, easy to do
If a problem is found - correct it and reset the car computer.
If no problem is found - buy a new downstream O2 sensor - install it , reset
as for
304 -Possible causes:
-- Ignition System.
-- Fuel Injectors.
-- Fuel Pressure.
-- Evaporative Emission System.
-- EVAP Canister Purge Valve.
-- Base Engine.
-- Running out of fuel.
Has the vehicle recently run out of fuel?
Yes
OBD II system OK. COMPLETE PCM Reset to clear DTCs. RETURN vehicle to customer.
Best of luck
