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My neighbor 2009 Corolla XRS, 138,000 miles, manual transmission and 2.4 l engine. Runs good but thirsty....not getting good mpg & check engine light is on. Found codes PO 138 (02 sensor bank 1 sensor 2); PO 607 (Control module performance); C1201 (Brake Boost sensor). Replaced 02 sensor, cleaned battery posts, replaced air cleaner, changed engine oil/filter and didn't notice any undue stress on any part of the wiring harness, especially near the 02 sensor. Vehicle also has a new MAF sensor. Still getting PO 138 check engine light and poor mpg....runs good. No other codes. Have run out of ideas. Need help.
 

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1995 T100 2WD & 1993 MR2
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What brand O2 sensor? How many miles on it since the sensor was replaced.
Longshot, pull the EFI rely for a minute or so to dump the energy from the ECM, then drive it, some say 50 miles others more. Clears the code and allows the ECM to relearn.
 

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Discussion Starter #3
What brand O2 sensor? How many miles on it since the sensor was replaced.
Longshot, pull the EFI rely for a minute or so to dump the energy from the ECM, then drive it, some say 50 miles others more. Clears the code and allows the ECM to relearn.
Pretty sure 02 was a Denso....from Advanced auto parts and now about 500 miles. When cleaning posts & battery cables were disconnected I disconnected the ECM to check harness wires/pins as it is right there next to the air filter.....but maybe not long enough? The next day the check engine light was back on.
 

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Denso is preferred. But between the battery disconnect and the drive It should've cleared and learned from the new data. Your above my pay grade already! Sorry :(
 

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Discussion Starter #6
Yea....I keep getting PO 138 & check engine which is the o2 sensor I replaced. I lightly scanned for a vacuum leak....didn't notice an idle increase hmmmmm. Will spray the engine area with starter fluid which should show a rpm increase if there is a leak. Didn't think of doing that before....this is why this forum is good. Keeps you thinking. A faulty other o2 sensor would have a different code. Maybe the cat converter is bad? Other than plugged I don't know how to tell. Don't know if a PO 138 code indicates a faulty sensor or if it is reading bad (too rich or too lean) exhaust?
 
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