The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, ad sets a P0420, or a P0430, depending on which bank it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter.
check for damaged parts loose connections oxygen sensors and catalyst convertor
If everything looks intact and that is your only code, you probably have a failing catalytic converter.
Catalyst efficiency below threshold (bank1) You may have a tired catalytic converter on bank 1.
P0420 = Catalyst Efficiency Below Threshold (Bank1). Sounds like you probably need to replace the Bank 1 (drivers side) Catalytic converter.
16803 - Main Catalyst, Bank1 Below Threshold 16803 - Main Catalyst, Bank1 Below Threshold
check for damaged parts loose connections oxygen sensors and catalyst convertor If everything looks intact and that is your only code, you probably have a failing catalytic converter.
Passengers side, after the catalyst.
where is bank1 sensor2 on the 1999 Mitsubishi montery sport 3.5
passenger side
On a 2000 Lincoln Town Car : Bank1 is the passenger side of the engine Sensor 2 would be in the exhaust AFTER the exhaust has passed through the catalytic converter ( downstream sensor , also called a catalyst monitor )
the one after the cat
It depends on which sensor, O2/camshaft,etc. The O2 sensor is a straight metal sensor that is screwed into the exhaust. There is an upstream/bank1-sensor1 or down stream/bank1-sensor2 after the catalytic converter. A camshaft sensor is an L shaped, usually black sensor that is installed into the head closest to the firewall(bank1).
O2 sensor circuit malfunction (bank1 sensor 2)
2, bank1 and bank2