I have a 2000 Ford Expedition with a SERVICE ENGINE LIGHT on. The code comes bask to the fuel mixture to lean. Should I suspect the lower oxygen sensor as being the cause?


The first thing I would suspect is that the engine is running too lean. The oxygen sensors are merely "messengers" to notify the computer and the driver, through the SERVICE ENGINE LIGHT that something is wrong, causing rich or lean mixture. The reasons can be many, such as ECM programming, ignition or lean fuel misfires, vacuum leaks, intake gasket leaks, faulty air and coolant temperature sensors, dirty mass air flow sensors, plugged air filters. My advice is "Don't Shoot The Messenger!" Have the problem diagnosed.

Jim O'Neill - Chino Autotech Inc., Auto Club SoCal AAR
SAE Int'l SoCal Section Board of Governors,
Vice Chair, Service Technology Programs
NASTF Service Information/Communications Committees
Auto Value/Bumper-To-Bumper CSC Nat'l Council
ASE CMAT-L1, CA. Smog Check Technician
AMI AAM Accredited Automotive Manager

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