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,

by in Guaynabo, PR on February 16, 2011
1 answer
ANSWER by , February 16, 2011
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.