I just got this truck and am learning about it. Has 83000 miles in fine shape with the only mod is a cold air intake. Had a CHECK Engine Light. As with anything I buy vehicle wise, I took it in for complete front to back service.Was told I had a vac leak at the pcv valve behind the super. I told my mech to repair. Anyway, 2 days later, my SERVICE engine light came on. The code was PO171. Was told the MAF sencors needed to be replaced. I replaced it with genuine ford MAF ($230) 2 days later same code. Was then adviced the O2 sensors were reading slow .Sorta scratched my head but I am not the mechanic. I replaced them (all 4) with genuine ford parts($300+). Upper right O2 was a bitch...lol..( BTY I disconnected the ground wire to batt on each repair to clear and reset cpu). 2 days later same code. So here I am asking what next......

 

Did you do anything to the truck just before getting the check engine light the first time? PO171 and/or PO174 codes almost always indicate a vacuum leak. Best place to start is to inspect all your vacuum lines closely for any signs of deterioration and be sure you have good connections.

 

Thanks for the response. No, it had the Check engine light on and Mech repaired the leaky PCV valve. The Check engine light hasnt been on since (2 months now) Its the Service engine light I am chasing.