05 Lariat while driving down the road engine goes into fail safe mode.
happen 3 times in last 2 months.Turn engine off restart no problems and does not leave any codes what gives?

 

Same problem with 08, have not had time to take to dealer but it always runs fine after turning it off.

 

Bone stock? No modifications?

If so, have your local stations recently switch to full 10% Ethanol blended gasoline?

If so, you are quite probably running lean and it's causing the PCM to set a lean code and go into Failsafe Mode.

There have been several threads related to Ethanol blended fuel causing lean conditions as well as poor fuel economy. Do a search for Ethanol or E10.

Take care.

 

My 08 5.4 Screw is 100% stock, I don't think so cal gas has the e-10 in it. Milage never varies much unless It's my driving habits. I watch milage carefully as it is usually an indicator of something else. I have several issues creeping up on this truck, rear power slider rattling, failsafe and the false neutral up shift on light acceleration at 2-3 shift. I have to take my shell off for them to work on the rear window, will do after holidays. Oh Ya the rotors are starting to shudder, I am not hard on brakes either. Truck has 8,000 miles.

 

I live in NH the fuel has been 10% ethenal for over a year now and i havent had any problems with my 08.

 

Keep the code reader handy and plug it in while the vehicle is running when this happens, not all codes are stored and you'll get any "live" codes this way.