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Old 09-03-2006, 10:28 PM   #1
JonR
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Member#: 22753
Join Date: Aug 2002
Chapter/Region: South East
Location: East TN
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2002 PSM WRX +PPG
OBXT

Default Front O2 Sensor Closed Loop Operation Only?

Hey all...got my car back from Protune the other day, was cruising around at 65 with cruise control on, got a CEL...1131 which is O2 sensor short circuit. Got home, reset the ECU to clear the code, made sure the O2 sensor was firmly plugged in and have not been able to replicate it since with a good 20 miles of driving.

I searched around but couldn't find a good answer as to whether the front O2 sensor is only used in closed loop operation ie cruise control and if so could this be why I haven't been able to replicate the problem or if it is used in OL and CL is it more likely that I just have a loose connection? Thanks
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Old 09-03-2006, 10:46 PM   #2
hondaeater69
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yes the front 02 is mainly for closed loop fueling (not used during open loop fueling). during OL fueling the ECU uses a fuel look up table with preset AFR's per load/RPM.
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Old 09-04-2006, 08:31 PM   #3
JonR
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Thanks that explains the problem...so the sensor is bad, but it just doesn't show up unless I'm in closed loop.
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Old 09-05-2006, 12:07 AM   #4
TMessick
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Well, the upstream(front) O2 is used for closed loop operation, but you should be able to get closed loop under "normal" driving as well as in cruise control. Depending on how it was tuned, you may end up going open loop very quickly though, which would potentially keep this diagnostic from running much during normal driving (and would probably make your fuel economy get evil). Poking around, P1131 looks like an "O2 sensor stuck lean" fault, which would be a rationality-type fault and not a "shorted low" fault (I think P0131 would be the sensor shorted low). Could still be wiring, but I wouldn't think so (I could be totally wrong though). I'm sure those with more Scooby experience will correct me...

If you want to have a look, just idle the car for a while -- you should definitely be running closed-loop at idle....
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Old 09-05-2006, 08:40 PM   #5
JonR
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Idled for 15 minutes and no CEL...that's why I was wondering what the problem could be. I'll probably replace the sensor anyway just to be sure.
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