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post #1 of (permalink) Old 04-13-2017, 11:30 AM Thread Starter
Z71
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Running rich bank 1 check engine light code

Vehicle: 2009 Impala LTZ, 3.9 liter engine


Several weeks ago, my engine check light came on for the first time in about 114k miles. The code retrieved in "running rich, bank 1.


I erased the code with my OBD II scanner, added some Chevron Techron fuel treatment into the tank fuel of non ethanol gas and repeated this twice. the engine check light stayed of for about 800 miles, then it came back as I started using E10 again.


Is there some common cause on these cars that thrown this code?
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post #2 of (permalink) Old 04-13-2017, 12:02 PM
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Could be a bad O2 sensor causing the computer to send too much fuel... Without looking up the code, that would be my best guess. Certainly not definitive though.

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post #3 of (permalink) Old 04-13-2017, 07:54 PM Thread Starter
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Originally Posted by jtrosky View Post
Could be a bad O2 sensor causing the computer to send too much fuel... Without looking up the code, that would be my best guess. Certainly not definitive though.

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How do these flex fuel cars determine the ethanol content in fuel? Is there a specific sensor that does that? If yes, where is it located? Because the check engine light did not come on while I was using ethanol free fuel for two tankfuls and then came on shortly after I started using E10, I suspect that this malfunction has something to do with improper ECU ethanol content self calibration to come on. I believe one needs a special GM scanner tool to be able to reset the ethanol fuel content within the ECU.
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post #4 of (permalink) Old 04-13-2017, 09:44 PM
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Yes, there is an ethanol sensor, but I don't know where it is. That could also be the problem. You can reset the ethanol content percent with a device like an HPTuner and probably a Tech 2 Not sure if disconnecting the battery overnight would reset it - but may be worth a shot...

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post #5 of (permalink) Old 04-14-2017, 06:09 AM Thread Starter
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Originally Posted by jtrosky View Post
Yes, there is an ethanol sensor, but I don't know where it is. That could also be the problem. You can reset the ethanol content percent with a device like an HPTuner and probably a Tech 2 Not sure if disconnecting the battery overnight would reset it - but may be worth a shot...

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I tried disconnecting the battery for about 2 hours. That apparently did not do the trick. I will try it for 24 hours, that's the easiest thing to try before anything else. Next I will probably try to reset the ethanol content in the ECU, but I do not have the Tech2 device. I will check eBay if I can find one at a decent price.
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post #6 of (permalink) Old 04-14-2017, 07:38 AM
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Not sure where you are located, but if you are anywhere near Philly, I have an HPTuner and can easily reset it for you... Tech 2 is VERY expensive. There are chinese clones, but I don't know much about them (there are other forum members that have them that may comment).

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post #7 of (permalink) Old 04-14-2017, 07:44 AM
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May google p0172 or search the forum up top for common causes/cures.
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post #8 of (permalink) Old 04-14-2017, 10:39 AM
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Check the % ethanol in fuel with scan tool to determine if causing over fueling.
Believe this is a known problem when switching between fuel types.
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post #9 of (permalink) Old 04-14-2017, 05:47 PM
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The 2009 does not have an ethanol sensor. The 2012+ models do. The '09 uses the oxygen sensors to determine ethanol content.
It is possible that when ethanol free fuel was used then e10 the computer couldn't compute the ethanol percentage properly, as it takes over 7 miles of driving after filling up with at least 3 gallons of fuel for the ecm to do its calculations. You will need a Tech2 to reset the percentage witch will force the ecm to recalculate. Otherwise you could wait until you can put more than 3 gallons into your tank, then clear the codes with an obd2 scanner and drive at least 8 - 10 miles and hopefully the ecm relearns.

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post #10 of (permalink) Old 04-14-2017, 06:20 PM Thread Starter
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Originally Posted by Bart77 View Post
The 2009 does not have an ethanol sensor. The 2012+ models do. The '09 uses the oxygen sensors to determine ethanol content.
It is possible that when ethanol free fuel was used then e10 the computer couldn't compute the ethanol percentage properly, as it takes over 7 miles of driving after filling up with at least 3 gallons of fuel for the ecm to do its calculations. You will need a Tech2 to reset the percentage witch will force the ecm to recalculate. Otherwise you could wait until you can put more than 3 gallons into your tank, then clear the codes with an obd2 scanner and drive at least 8 - 10 miles and hopefully the ecm relearns.

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The problem is that when I got the code P0172 (check engine light) I was still using usual regular E10 unleaded and that is all I have ever used in this car since new (now at 115k miles). I filled up with ethanol free gas after clearing the code, and added some Chevron Techron injection cleaner to the tank. I ran two ethanol free fuel tankfulls and drove the car about 700 miles without the engine check light coming on. Then I started using E10 regular unleaded again (as the ethanol free 90 octane costs about 60 cents more per gallon) and the engine check light came back on after about 1/2 of that tank. Same code again. My scanner also says that there is no code stored in the ECU.

So it is not possible to reset the ethanol content recorded in the ECU by disconnecting the battery for at least 24 hours? If not, I will have to take the car to a GM dealer to reset it with the Tech 2 tool. Which Oxygen sensor determines the ethanol content? The one upstream of the catalytic converter, or the one downstream of it, or both?

I live in Central Florida.
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post #11 of (permalink) Old 04-14-2017, 07:05 PM
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Downstream o2's should just monitor cat efficiency. Does your 3.9 have an upstream for each bank and a downstream for each bank?
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post #12 of (permalink) Old 04-14-2017, 07:53 PM
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Unfortunately Disconnecting the battery will not reset this perticular setting and it's the upstream O2 sensor that the Ecm uses for its calculations.

This is how GM describes how the calculations are done

"The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sensor output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence.

After a re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either American Society for Testing and Materials (ASTM) Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected ethanol mix in the fuel tank, and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop operation. "

Last edited by Bart77; 04-14-2017 at 08:02 PM.
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post #13 of (permalink) Old 04-14-2017, 08:35 PM
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I got a 3.5 and i got the same code i replaced the mass air flow sensor and that took care of it.

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post #14 of (permalink) Old 04-15-2017, 03:31 AM
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Sorry for the mis-information on the ethanol sensor... Didn't realize that pre-2012 8th gens didn't have an actual ethanol sensor. Thanks for all of the great info, @Bart77 - you are an invaluable member of this forum!

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post #15 of (permalink) Old 04-15-2017, 06:09 AM Thread Starter
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Quote:
Originally Posted by sheila View Post
Downstream o2's should just monitor cat efficiency. Does your 3.9 have an upstream for each bank and a downstream for each bank?
There is only one upstream oxygen sensor and one downstream sensor.
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