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Yuta Yuta is offline
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Join Date: Jul 2012
Posts: 108
Will an aging after-cat o2 sensor affect MPG?

i have a 02 boxster... had ECL on. The code was P0139 which means aging of after cat o2 sensor... From what I read, the pre-cat sensor adjust the mixture while the after cat sensor only check if the cat is functioning. However, my MPG is reduced significantly. Before I had around 25, then it was 18 to 22. I am confused.... which sensor should I change? Or maybe change all of them??

A few days after the ECL went on, my battery died... I had to change the battery.. after new battery was installed, the ECL was gone... However, the MPG was stil arund 20-22..... I am kinda certan the o2 sensor problem still exists,....
Old 01-11-2013, 08:28 PM
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