OBD Operation Summary for Fiesta - MotorCraftService.com

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HO2S MonitorUpstream Oxygen Sensor Monitoring - Switching SensorThe upstream oxygen sensor circuit monitor detects if the HO2S sensor voltage is above or below a calibratablethreshold or if it is not active, (lack of switching) or stuck at the bias voltage.The upstream oxygen sensor monitor detects if the HO2S signal circuit voltage is:Shorted to ground or an air leak is present (low signal),Signal circuit voltage is high (high signal),Open circuit causing the signal circuit voltage to be inactive or stuck at the bias voltage.The open circuit detection strategy is described belowOpen Circuit CheckThis check detects if the HO2S signal circuit is not active (lack of switching) or stuck at the bias voltage at the beginningof the driving cycle. This check allows the service technician to find the root cause of the upstream HO2S sensor "notready for closed loop”. If the "open circuit check" stores a DTC (P0130) then an additional DTC is also storedautomatically (P016A ) - O2 Sensor Not Ready (Bank 1 Sensor 1)).This additional check is performed because there are two different possible root causes for this symptom at engine start.The upstream signal voltage can be inactive (stuck at the bias voltage) because of an open circuit, or because of a weakHO2S heater. These cases are described below:Case 1: HO2S Open Circuit at engine startAn open circuit power integral starts and activates the open circuit diagnosis to check if a real open circuit is present or ifthe P016A was set because of a weak O2 sensor heater.If the power integral exceed its limit, the signal is checked again. If the signal voltage is still stuck at the bias voltage andthe internal resistance is above a calibrated limit, a P0130 is stored for an open circuit.Case 2: HO2S heater low performance at engine startThe open circuit power integral starts and the signal is checked again. The power integral is calibrated based on lowactivity of the signal voltage with a weak heater. After the power integral exceeds its limit, and the upstream voltage isoutside the open circuit limits, if no real open circuit present, the P0053 for the heater rationality upstream is stored.CONTINENTAL REVISED: SEPTEMBER 17, 2010 PAGE 36 OF 111
Upstream HO2S Circuit CheckNoStartMonitoring conditionsfulfilled?YesNoNoVolts low = SCG / air leakorVolts high = SCVBorVolts at bias = Open CircuitYesError counterdecrementError counterincrementError counter>= threshold ?YesOxygen sensor circuit malfunctionSignal line short to battery voltageSignal line short to ground orOpen circuitFault processingCONTINENTAL REVISED: SEPTEMBER 17, 2010 PAGE 37 OF 111
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OBD Operation Summary for Fiesta - MotorCraftService.com

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