NOTICE: The information contained on this site is presented for information only. OBD-Codes.com is not responsible for any actions you take on any vehicles. If you have any doubt as to repairs on your vehicle, please contact a qualified technician. Lack of HO2S-21 Switch, Sensor Indicates Lean A Heated Exhaust
Oxygen (HO2S) sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time. You will likely not notice any drivability problems. A code P1151 may mean that one or more of the following has happened: * Short to VPWR in the harness or HO2S * Water in the harness connector * Open/shorted HO2S circuit * Corrosion or poor mating terminals and wiring * Damaged HO2S * Damaged PCM * Excessive fuel pressure
Leaking/contaminated fuel injectors
Leaking fuel pressure regulator
Low fuel pressure or running out of fuel
Vapor recovery system * Air leaks after the MAF * Vacuum Leaks * Improperly seated engine oil dipstick * Leaking gasket * Stuck EGR valve * Leaking diaphragm or EVR * Oil overfill * Cam Timing * Cylinder compression * Exhaust leaks before or near the HO2S(s) * See the above list of causes and go from there. Sources: MotorCraftService.com
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