Had head gasket replaced than engine light came right on P0430 2002 Nissan Sentra -

Question

Head gasket was replaced and when I drove car home the engine light came on, PO430. Sent car back to garage and they just kept clearing the engine light. They did tell me a couple of the o2 sensors were not in correctly so they switched it. I was sick of it so I took it to another garage. The second garage told me it must be the front converter and it will cost $1100 plus I need to replace all 3 o2 sensors. Than, sent it to a 3rd garage and they told me there are 4 o2 sensors and they would replace all for $1250. After reading, no one checked the correct placement of o2 sensors. Also, no one checked spark plugs. How do I know what catalytic converter it is> Someone told me the back cat was very rusty. Could it be the back catalytic converter? I never had a problem until they changed the head gasket.

Answer 1

P0430 3 way catalyst  function

Here is what  degrade a catalytic convertor, coolant seepage, prolong misfire, using oil, and yes a headgasket.In order for you to code up a P0430 the 02 sensor needs to be in porper working order, It is the rear 02 sensor that increases in activity this informs the ECM that the convertor does not have oxygen storage capability.You do not need to replace any of the 02 sensor just the catalytic, Before a catalytic is to be replaced the engine performance should be inspected,

Answer 2

If the car was not running properly it might have damaged the catalytic converter  or if you use low octane fuel and oxygen sensors, was the car burning coolant or mixing coolant with the oil? there is a very small chance that the catalytic converter is not bad and it is an oxygen sensor the sensor sensors can be tested with the correct scan tool. alot of the time catalytic converter and oxygen will have to be replaced to fix the problem. 

Everything else should be checked before replacing the catalytic converter

other possible causes besides catalytic converter:

Exhaust tube

Intake air leaks

Injectors

Injector leaks

Spark plug

Improper ignition timing