my friend told me if O2 sensor doesnt work
it would make my car run a lot richer and that will eventually make my car to run slower....
bu other friend told me only if ur primary O2 sensor isnt working but secondary O2 sensor doesnt really do to car's performance.....

what is right?

 

The ECU uses the primary O2 signal to run the car. The secondary one (in the cat) just tells the ECU how well the cat is working, nothing more. The only problem with this is that the CEL you get with a bad cat sensor is that it will mask another code should one come along.

 

The ECM continuously monitors the 3way cat efficiency via oxygen sensor feedback. By comparing the switching frequency of front and rear o/2's it can determine the efficiency of the cat. The ECM reacts to the o/2 sensor signal and controls the time the injectors are held open to maintain stoichiometric ratio based on the signal received.

The rear o/2 monitors oxygen levels in the exhaust gas after the conversion process. Even if the switching characteristics of the front o/2 sensor shift, the voltage signals from the rear o/2 sensor control the air/fuel ratio to stoichiometric.
If the o/2 sensor fails feedback control changes from closed loop to open loop.

 

are u saying that the secondary (rear) O2 will also could effect the performance of the S2k?

cuz i think my S runs slower now i dont know maybe in my head but let me know thank you

 

I think the 2nd has some thing to do with performance. My car runs real rich when the CEL is on from the CAT O2. I put a 10 watt 13 ohm resistor on the wires that go's to the CAT and no more CEL. And the car runs great.

 

The primary heated oxygen sensor (HO2S) (Sensor 1) is installed in the exhaust system. It detects the oxygen content in exhaust gas and transmits voltage to the engine control module (ECM). The ECM monitors the primary HO2S voltage value and controls the amount of injected fuel (air/fuel ratio feedback control) so that the air/fuel ratio is close to the stoichiometric air/fuel ratio. The air/fuel ratio correction coefficient for correcting the amount of injected fuel is the short term fuel trim. If the primary HO2S voltage is low, the air/fuel ratio is lean, so the ECM uses A/F feedback control to issue a Rich command. If the primary HO2S voltage is high, the air/fuel ratio is rich, so the ECM uses A/F feedback control to issue a Lean command.



The secondary heated oxygen sensor (HO2S) (Sensor 2) is installed downstream of the three way catalytic converter (TWC). The HO2S detects the oxygen content in the exhaust gas downstream of the TWC during stoichiometric air/fuel ratio feedback control by the engine control module (ECM) from the primary heated oxygen sensor (HO2S) (Sensor 1) output voltage, and its output voltage is used to control the air/fuel ratio so that the TWC efficiency is optimized.


Basically, the Primary 02 is used for keeping the engine running in the AF#'s the PCM wants it to based on Load, throttle position, etc.

The secondary is used to monitor convertor function.

 

The resistor only addresses the 02 sensor's heater circuit DTC. It does nothing to fool the other DTC's covering sensor output. Stock S2k's run rich at WOT. Since your car no longer has a convertor scubbing off NOX, HC's and C02 as well as a slightly less restrictive exhaust, It's definitely running "dirtier" than before. You're smelling the HC's the convertor used to scrub out of the exhaust stream.

 

The only code my car ever gets is 2nd. o2 heater circuit. Should other codes come up?

 

There are both DTC's for 02 sensor voltage output, and convertor efficiency.