I have a 2006 Nissan Altima 2.5 4 – I replaced the pre-cat with a header because I heard that they would break apart and ruin the engine. However, now the engine light keeps coming on. Will an O2 sensor simulator fix the issue. I have tried to put a spacer on the header, but that did not help. I am told there are 2 o2 sensors, but only find 1. Thanks for any help!!
Removing Catalytic Converter
Replacing the exhaust manifold with a header is generally done for performance reasons (note* the exhaust manifold and catalytic converter are one assembly). There is nothing that would break apart and enter the engine as far as the catalytic converter is concerned. This is because it is mounted out the output side of the engine cylinder head.
Using O2 Sensor Simulator
The original setup includes two oxygen sensors. One before the catalytic converter and one after. The Oxygen sensor that is mounted before the (upstream)converter is used to determine air/fuel mixture. The O2 sensor mounted after the converter(downstream) is used to determine the efficiency of the converter. So if the simulator you are proposing to use is to fake out the downstream sensor, then yes it should take care of the check engine light issue.