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Discussion Starter #1 (Edited)
Cobalt Owner Asking Non Cobalt Related Question, Yeah It's Happening!!

Question for you guys. My gf's car has been blowing on gas milage for quite a while now. I've tried seafoam in the intake and gas can, and changed plugs (that were corroding). She is still getting bad milage, and her OBD2 reader always comes up with cannot connect (someone obviously messed with it at one point a fter taking a look under the dash). I'm thinking it might be her oxygen sensor but at $100 a piece I want to make sure I get the right one so I dont spend $200 guessing. Any way to tell for sure other than a code being thrown?

Also, when its really cold after start up it will buck as you push on the gas. RPMS go up and down from 800 to 2000 until it starts to warm up. Hasn't done it as much since I changed the plugs.

All fluids are full, dont know when the last time tranny was flushed but it shifts like a dream. It is due for an oil change but I have done those myself since she bought the vehicle last year so thats probably not the problem.

Any help would be appreciated.

---------- Post added at 06:08 PM ---------- Previous post was at 05:30 PM ----------

11-15-2012, 06:06 PM
money_man
Expert Join Date: Mar 2012
Location: Halifax, N.S
Posts: 753

My rear o2 took 7mpg from me. Is there a check engine light on?

---------- Post added at 06:09 PM ---------- Previous post was at 06:08 PM ----------

No, no check engine light. But because of the look of the OBD2 reader I wouldn't be suprised if it was disabled.
 

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Levee
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The only way to disable a code is to reflash the tune of the ecm. Is there an exhaust leak?
 

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Discussion Starter #3
Not that I am aware of. Car seems to run properly. I know she is a pretty agressive driver so I would account some of the bad millage to her habits, but a 00 Nissan Maxima should not be getting 17mpg no matter the driver since we travel mostly over 50mph to and from work.
 

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What motor? 2.5?
 

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what kind of car is it? Also check Rock Auto for the o2 sensor... they are usually the cheapest you can find.
 

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My Nissan spec V was doing the same thing with no code but I traced it to the front o2 sensor.
 
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