P0031 Possible Bad Gas from Costco

So, I went out to start my car today for the first time of the day and immediately noticed the Christmas tree lights (flashing cruise and parking brake, and lit up check engine and traction control). Before pulling the code I checked the gas cap...rubber gasket seems to be in great condition. Pulled the code and got a P0031 oxygen A/F sensor heater control circuit low bank 1. Rewind to about a week ago I'm researching about Costco gas (I recently purchased a membership) since they sell 93 octane at the one near me. Some avoid it like the plague, others have used it for years with seemingly no ill effects. I decided to try it out so I filled my almost empty tank with it. Within about 50 miles I noticed my mileage was down a bit (I watch/track my mileage like a hawk). It's up to 10% ethanol, which I try to avoid. Up till today everything seemed okay, minus the slight decrease in mileage. Now I'm wondering if the gas caused my code. Drove the car today for about 30 miles and there are no symptoms whatsoever, just all the lights.

 

Has anyone else had an experience like this?

What are the odds that my upstream 02 sensor is failing/failed? Car is stock with 135k mainly highway miles.

I didn't have a chance to troubleshoot otherwise today. I plan to check fuses/relays (I thought there was one related to the 02 sensor(s)). I'll also obviously get under the car and check the sensor harness and make sure I didn't burn through a wire or something silly like that.

Any other thoughts? Thanks in advance!

My mechanic suggested that I only use Chevron, but I've been using Shell because I fell for the anti-carbon buildup marketing.

 

One time when I had the FXT in his shop, he had me listen to a noise under the intercooler when the car was off. he said it was due to lower level gas. I didn't hear much, but took his word for it. I was using Costco at the time.

Costco is top tier gasoline so I find that odd

I have been running Costco gas for the nearly 4yrs I've had my GT. I only had issues where my DAM would drop when I didn't use Costco gas and went to some random station

I would think if the gas was bad enough to throw off your AFR, then it would also be running like complete garbage.

 

At 135k, I'd imagine the O2 sensor is probably on its way out.

I use Racetrack gas, its what I was tuned on, no knock issues with it or shell for that matter. But I notice a drop in MPG with the shell.

 

I second Rutchard 7ish years is a long time for an O2 sensor to last. And since the fault is in the heater circuit not the sensor part it pretty well eliminates all but a wiring issue at the sensor/plug.

Based on these findings. I may have to give Costco another chance. The Shell 91 is pricey!

I run Costco gas in my Stage 1 FXT and haven't ever had gas related issues.

 

The LGT runs on corn so Costco isn't an option around here.

We pretty much run Costco gas exclusively in both of our cars (cheapest top-tier gas around) for years now without an issue...other than long lines on the weekend to get gas!

no issues here....

Costco is not immune from a bad batch or a driver stirring the tank right as you are filling up, have had a few friends run into that... That said, I don't recall getting a bad tank of gas from Costco in the last 10 years.

Thanks for all the replies. Everything on/under the car seems to check out so I just placed an order on a Denso replacement. Hopefully that'll clear the code for another 7 years or 135k miles. Still on the fence about the Costco gas, but thinking I'll give it another shot in the future.

I like using BP. I use the same gas station every time with no problems.

I like using BP. I use the same gas station every time with no problems.

 

BP

 

 

 

After the massive spill that killed our coastline for years...

 

 

 

 

Being consistent in my opinion is most important.

Filled up with Costco gas a few days ago. When I turned the car off, there was lots of popping and snapping noises. Going back to Shell. Your results my vary.

 

BP is the cheapest best gas around me..... *shame*