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Old 02-26-2012, 04:20 PM   #1
limenuke
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Post-Cat O2 Sensor

I need to replace my post-cat O2 sensor. A CEL went on about 2 months ago - which I cleared- but it has not come back. Regardless, I'm finding it hard to stay below 12L/100km and I am not driving in a spirited way and I'm very conscious of how much I'm gassing.

I hear that the post-cat O2 sensor doesn't do anything for fuel...does anyone have any ideas?
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Old 02-26-2012, 04:48 PM   #2
T.Dot_E30
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Post cat 02s dont effect the mixture, They are there only to monitor the performance of the catalytic converters.

If you don't have a CEL, then i wouldn't worry about the o2 sensors until you are able to get a real-time reading to see if they are reading correctly.

Until then make sure the basics are in working order. Spark Plugs, Clean Air Filter, Fuel Filter, make sure there are no vacum leaks, maybe run some injector cleaner through the system and that the engine is warming up to normal operating temperature (a stuck t-stat will keep in engine in cost start mode and burn more fuel.

Also keep in mind that winter driving usually burns more fuel if you idle alot or let it sit to warm up.
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Old 02-27-2012, 10:54 AM   #3
tehskeo
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Post cat sensors are there only to monitor how well the cats are working. The pre-cat sensors are monitored for rich/lean mix.

Replacing a post-cat sensor shouldn't affect fuel economy. Likewise, a damaged post-cat sensor should not affect fuel economy.

T.Dot made some good points RE: winter and general maintenance. What was the CEL code that you cleared?

**Disclaimer: While I didn't pull that info out of my ass, I have no credible source other than personal experience and what I've read on forums over the years.**
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Old 02-27-2012, 11:41 AM   #4
limenuke
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It was P140, no circuit activity from O2 Sensor Bank 1 Sensor 2.
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Old 02-27-2012, 08:54 PM   #5
tehskeo
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Hmm, that could be a number of things. I'd say don't worry about it until it happens again. See if you get another code in the next few days. Also, remember if it's a particularly cold day. It might just have trouble getting up to proper temp in the morning when you first start it.
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Old 02-27-2012, 11:55 PM   #6
limenuke
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It hasn't happened for a while and the day it happened, the car was travelling a 118kmph at 3k RPM. So, I doubt it wasn't hot enough.. =\ hmm
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