Function of downstream O2 sensor on Pontiac Vibe?

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Mar 23, 2005
Hi Does the downstream O2 have any effect on engine management or does it read temp only and throw a code if out of temp range? I'm replacing the upstream due to degraded fuel economy and age - 150k. If the downstream does not effect engine management I am going to leave it.
As far as I know, a downstream sensor monitors cat efficiency and if the upstream sensor is malfunctioning, takes over for it. There's no need to replace it unless it's throwing a code.
if the upstream sensor is malfunctioning, takes over for it
It cant take over for it, the downstream O2 monitors that catalytic action has taken place by comparing readings pre and post cat. OP. If your changing one its good policy to change both, they do get lazy.
All it does is 'see' a change from the first one. If the readings stay the same, you'll throw a code - the cat is not working right.
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My '04 Vibe threw that catalyst inefficiency code(I don't remember exactly what it said now). Fuel mileage seemed to go down to me, but maybe I wasn't watching it close enough. So I did the spark plug anti fouler trick, cleared the code, and it never came back. That was about 15k miles ago. Car has 167k miles on it now. Mileage is as good as ever.
I wouldn't replace it. It doesn't matter if that one gets lazy. From its perspective, that just means the cat is working well.
Originally Posted By: Vikas
And a sensor extender, also known as spark plug anti-fouler, makes a sensor lazy.
I'm doing that this week. 95% efficiency P0420.. not fair. 1/2" drill bit and a vice so people say, just ordered the kit off amazon. Wonder if the insp people will look for it or recognize it..
Do you shop for inspection station or take it to your usual place who knows you and your vehicle? By the way, single anti-fouler may or may not work. You are better of purchasing a stainless one from ebay for $15. - Vikas P.S. $275 for that eBook! Methods for monitoring and diagnosing the efficiency of catalytic converters ... Wow!!!
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