Ford Explorer P2198 code

Sure, just a guess at this point but HEGO is Suspect!~~ Here's the complete follow through. Generally, you should begin troubleshooting with the lowest numbered code. There are quite a few items common to all the codes. Below, I have defined the code and what sets it. Then there is a list of causes. Unless you want to start shotgunning parts, I would use this list to check everything that can be checked. I would concentrate on fuel and induction systems. That being said, however, it is quite possible the O2 sensor for bank 1 is bad. P0171 - System too Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors the fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. Refer to Section 1 , Powertrain Control Software, Fuel Trim for more information. Some of the causes for this are: Air Measurement System: MAF sensor (contaminated, damaged, malfunctioning, etc.) Fuel System: Fuel pressure regulator (leaking, malfunctioning, etc.). Fuel filter plugged, dirty. Fuel pump (weak, check valve leaking, etc.). Leaking/contaminated fuel injectors. Low fuel pressure or running out of fuel. EVAP canister purge valve leaking (when canister is "clean"). Fuel supply line restricted. Fuel rail pressure sensor (incorrect reading). Air Induction System: Air leaks after the MAF. Vacuum Leaks. PCV system (leak, valve stuck open, etc.) Improperly seated engine oil dipstick. P2198 - Lack of HO2S-21 Switch, Sensor Indicates Lean A HEGO sensor indicating rich at the end of a test is trying to correct for an over-lean condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time. P2198 have common causes: Electrical: Short to VPWR in harness or HO2S Water in harness connector Open/Shorted HO2S circuit Corrosion or poor mating terminals and wiring Damaged HO2S Damaged PCM Fuel System: Excessive fuel pressure Leaking/contaminated fuel injectors Leaking fuel pressure regulator Low fuel pressure or running out of fuel Vapor recovery system Induction System: Air leaks after the MAF Vacuum Leaks PCV system Improperly seated engine oil dipstick EGR System: Leaking gasket Stuck EGR valve Leaking diaphragm or EVR Base Engine: Oil overfill Cam timing Cylinder compression Exhaust leaks before or near the HO2S(s) Regards