Injection cleaning on 2008 Mercury Mountaineer

Hi,
I am getting Check Engine Light, I used my scan tool and got his Error Code:
1- P0171 -- FUEL TRIM TOO LEAN (BANK 1)
2- P0174 -- FUEL TRIM TOO LEAN (BANK 2)

What happened I was driving and need to refill car with fuel, I used to fill it with Octane 95 Fuel, but at that time I were not able to find it so I fill it with Octane 91, after driving for two days this light appears and I got this Error code.

Could please advise if this is a serious problem or not.

Regards,

Asked by for the 2008 Mercury Mountaineer
1 answer
First do a visual inspection for vacuum leaks like a hose disconnected,and make sure the hoses that go to the intake are connected.There was a service bulletin for these codes that had to do with running e-85 fuel on vehicles that are not flex fuel capable.If nothing obvious is found you will need to take the vehicle to a dealer for an accurate diagnosis.