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Old 12-20-2013, 11:41 PM   #1
Scooby Newbie
Member#: 360509
Join Date: Jun 2013
Chapter/Region: E. Canada
Location: Windsor, Ontario, Canada
2005 2.5RS Wagon

Default CEL reset and hasn't come back..

Hey guys I'm not sure if somebody has a post like this but anyways...

So one day I started my car a couple minutes after shutting it off (running into a store) and I had the dreaded check engine light and cruise flashing.
I just did a quick walk around the car and opened the hood to "check" the engine, everything seemed fine.
So the next day I took it to my friends house who has a code reader. The code P0131 (O2 sensor low voltage bank1 sensor1) was coming up, we decided to reset it and I was on my way.
It has been a couple of weeks now and the light hasn't come back, I've driven the car many miles since on highways and in the city.

My main question is, if the O2 sensor was actually messed up, would the engine light come back? Or does reseting the ECU simply clear the light but keeps the code in the computer?

I'm mainly concerned because I need a stupid E-TEST CASH GRAB test soon...

My friend is out of town for christmas and I don't have my own code reader.

Thanks for anybodys help!
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Old 12-27-2013, 03:12 AM   #2
Scooby Newbie
Member#: 251743
Join Date: Jul 2010
Location: C.V. Ca

If there is a low voltage from the primary O2 sensor for a longer than anticipated duration this indicates that the engine was running lean. This could be from any number of things, a hiccup, a sensor that is becoming lazy/worn(needs to be replaced), or some other issue that was caused in the drivetrain due to a faulty component or air intake leak elsewhere.

If you can beg/borrow/steal a scanner(not a code reader) and monitor the O2 sensors voltage output it should be switching back and forth from .1V - .9V normally. Using an unlit propane torch you can artificially create a rich mixture into the intake, or a lean mixture by pulling a vacuum hose off. Watch the O2 sensors voltage and cross counts. If the switching is slow/lazy or hovers around a single voltage, then the O2 is probably in need of replacement.

If the car has not had a tuneup/o2 sensor replacement in quite a while it may be time to freshen up the engine a bit.

Just because an O2 doesn't set or maintain a hard fault code, does not mean it is working optimally.
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Old 12-29-2013, 10:19 AM   #3
Elbert Bass
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
2016 Fuji Sunfire 03



Last edited by Elbert Bass; 12-29-2013 at 10:25 AM. Reason: Canadian vehicle so US service data may not apply
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