Thanks, but let me rephrase. How do I tell if that is from the downstream sensor or the pre-cat sensor? Specifically, is this causing the car system to run rich?
From Kyle's previous post:
<begin snip>
With that being said, if the code(s) that you are pulling pertain to an O2 heater circuit failure on the DOWNSTREAM sensors...it will not cause the car to run poorly or decrease gas mileage. That is strictly a "wear" code for the rear O2s. The rear O2s are not the arbiter when it comes to fuel trim..that is still the job of the pre cat sensors. Likewise, O2s do not play any role in WOT operation....the PCM goes to power enrichment and a pre-destined fuel and timing map based on load and throttle angle. The rear heater circuit failure will only appear after the magic number of key cycles and is nothing more than a self-test that the PCM performs on the heater circuit in the O2s...how quickly the O2s lite gives the PCM an idea of their condition.
<end snip>
