thanks for the advice.
Originally Posted by Mike
The upstream sensor is really only there for the computer to monitor fueling conditions(fuel trims). The downstream sensor is only used to see if the cat converter is working or not.
The only real benefit of changing the upstream sensor is if you have a diagnostic scanner that can reset the learned fuel trim values your ECU has stored. Otherwise, changing the upstream would be moot.
So, since the upstream sensor is working it is better left untouched?
What would be the effect of not replacing the downstream sensor?
I understand that it measures the O2 concentration in the exhaust gas so that the PCM is adjusting the injected fuel accordingly. Now, since the sensor doesn't report any value, does the PCM use a fallback program with assumed O2 values? Or does it estimate the values based on the upstream sensor?