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Discussion Starter #1
I have a 2008 Cobalt with a 2.2 litre engine, automatic transmission. Vehicle has 45K miles, and about 95% of driving is on the Interstate @ 70 MPH. About once a month, the "Check Engine" lite comes on for about 2-3 days, then will go out. Spits out a code P2271, HO2S Signal Stuck Rich Bank 1 Sensor 2. Before I take this to the repair shop, does anyone have any ideas what might be causing this code? The car runs great, and performance/fuel mileage do not seem to be affected. Like I said before, it's very intermittent, AND seems to occur shortly after refueling. I do not try to squeeze more fuel in after the gas pump clicks off, (I know that's a no-no), not so sure that my GF doesn't try to overfill. I've told her not to, but ?????. Any thoughts are appreciated! One last thing, is Sensor 2 the "Downstream" O2 sensor? Thanks!
 

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I believe that is the 2nd O2 sensor, after the cat. Probably going bad, although it shouldn't be. Others can correct me if I'm wrong but that code should mean that there is an incorrect cat flow/ratio. Maybe the cat is bad.
 

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It is the second one after the cat. If I were you I would disconnect second HO2 sensor and clean contacts and maybe add a little dialectric grease to keep moisture out, then re-assemble. Try it if error comes back maybe your cat is tired. Do you run gas only or E85?
 

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This is from a GM service bulletin;

• Only vehicles that are listed in the E85 Compatible Vehicles section of this bulletin and/or www.livegreengoyellow.com are E85 compatible.
• All other gasoline and diesel engines are NOT E85 compatible.
• Use of fuel containing greater than 10% ethanol in non-E85 designated vehicles can cause
driveability issues, service engine soon indicators as well as increased fuel system corrosion.
• Repairs to non-FlexFuel vehicles that have been fueled with E85 are not covered under the terms of the New Vehicle Warranty.

Notice:
• Misfire codes (P0300).
• Various O2 sensor codes.
• Disabled traction control or Stability System disabled messages.
• Harsh / Firm transmission shifts.


The only E85 compatible vehicles produced by General Motors are:
• Fuel system and / or engine mechanical component degradation.
• 2000-2002 S-Series pickups with 2.2L (VIN 5- RPO L43)
• 2002-2005 full-size pickups and utilities with 5.3L (VIN Z -- L59)
• 2006 Chevrolet Avalanche, Silverado, Suburban, Tahoe with 5.3L (VIN Z -- RPO L59)
• 2006-2007 Chevrolet Impala, Monte Carlo with 3.5L (VIN K -- RPO LZE)
• 2007 Chevrolet Avalanche, Suburban, Tahoe with 5.3L (VINs 0, 3 -- RPOs LMG, LC9)
• 2007 Chevrolet Express, GMC Savana with 5.3L (VIN Z-- RPO L59)
• 2008 Chevrolet Impala with 3.9L (VIN 3-- RPO LZG)
• 2006 GMC Sierra, Yukon, Yukon XL with 5.3L (VIN Z -- RPO L59)
• 2007 GMC Yukon, Yukon XL with 5.3L (VINs 0, 3 -- RPOs LMG, LC9)
• 2007 Saturn Relay, Buick Terraza, Chevrolet Uplander, Pontiac Montana SV6 (Canada Only) with 3.9L (VIN W -- RPO LGD)
 

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Good morning lugnutz59,

I see you've gotten some great insight, and that you were planning on having this looked into. Have you made any progress on this since your last post? If you decide to work with a dealership, please let me know as I'm available to assist in whatever way I can.

All the best,
Sarah
GM Customer Service
 

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Discussion Starter #7
Thank you, Sarah. I do want to have the vehicle repaired. So far, the only thing I have done is to add a can of "Seafoam" to a full tank of fuel. I'm going to drive it a few days and see what happens, if anything. If the problem persists, I will replace the Downstream O2 Sensor, and if that doesn't fix the problem, I'll have to take it to the Dealer. As a side note, I was a Certified Chrysler Master Technician, retiring in 2004 due to health issues. So I do have an idea how this stuff works, but I also know that without a scan tool, I'm just a "babe in the woods" lol. I will keep everyone up to date as I chug along. TIA:thanks
 

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Discussion Starter #8
Well, I ran a can of Seafoam through the fuel system, the CEL went out for a few days, but is back on again. My next step is to replace the Down-Stream O2 sensor, and hope that cures the problem. I will also give the Cat Converter the "rattle" test, just for giggles.
 

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Discussion Starter #9
OK, I "checked" the Cat Converter and no internal rattle. So I Replaced the Downstream O2 Sensor, using an "Exact Fit Bosch O2 Sensor" from AutoZone. I didn't use an OEM Sensor as my local dealer uses Matrix Pricing on their parts, and the price was about double the cost of the Bosch sensor (And I worked at the Mopar Division of this same dealership for 10 years!). The CEL went out, car ran great, and I gained about .3 MPG Average Fuel Mileage. Three days later, Check Engine Light came back on. So, it's off to the dealer (Ugh!!). Probably will have to buy an OEM sensor and go from there. Can't do much else without a Scan-Tool!
 

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Scans are free at O'rieleys and most other local parts stores.
 

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dont cheap out on the o2 sensors. I bought a bosche one and went bad in 2 days, replaced under warranty and it went bad again in like 3 days. I decided it was worth my money to just buy a dealer one and havent had any problems in 3 months.
 

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Discussion Starter #12 (Edited)
I think that may be my next step, money man. I had the car in the dealership this past Tuesday. This time the fault code (P0054) showed that the O2 Sensor Heater was bad. The tech reset both the fuel trim numbers and the O2 Sensor Heater Resistance Learn. He tested everything, and of course, everything worked fine :x Sounds fishy, but the Service Writer showed me the service manual and it did state that when replacing either O2 sensor, the ECM needs to have these values reset. Now, today, Thursday (and 3 drive cycles), the Check Engine Light is on again (Not sure what the code is now). It's about 30 miles to the Dealership and AutoZone (the nearest place to me that will read the codes for free). I'll stop at the dealership tomorrow and set up another appointment. But I know in the past, I have had multiple problems with aftermarket O2 sensors, figured that by now, Bosch could make a replacement sensor that would work!? More on my saga later. Thanks for everyones suggestions!
 

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Discussion Starter #13
Chapter XII; "The Fix" I'm gonna call this one fixed, at least for now. Had AutoZone check codes again and came up with "P0139 Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 2)". The partsman told me my O2 Sensor was no good, guess he forgot he sold me a Brand New one a couple weeks before! LOL!! So I went to the dealer, and they gave me the part # for a new "DownStream O2 Sensor". Said they could have it in 3 days. Then the more I thought about it, in my days wrenching for Chrysler, quite often, the parts book listed the wrong O2 sensor for a particular application, and we would end up using the part # that was etched into the old O2 Sensor. Luckily, I still had my old Cobalt sensor, and the part # stamped on the sensor housing was different than the Dealer told me. Double checked with the dealer, they said the part had not been supersceded. So, armed with my old sensor number, searched the Internet and found a NEW AC/Delco O2 sensor with the same part number as mine (and $30 cheaper than the Bosch sensor!) Ordered the sensor, R&R sensor, and the Check Engine Light is out!
Car has been through (7) 30 mile drive cycles and so far, so good! The car runs great, 32+ MPG, I'm a happy camper. Thanks to you all, and especially money man, in my 30 years as a tech, I never saw an aftermarket O2 Sensor that worked, I just figured that Bosch ( who makes sensors for a lot of vehicles) would be a good choice. Should have known better! FWIW, AutoZone did refund my purchase, no questions asked. I hope this experience will help someone else! Thanks!
 

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Glad you got it fixed. My sensor from the dealer was $230 :(
 
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