Code question: PO147
Code question: PO147
#2
12-09-2013, 05:53 PM
year/make/model??
ASSUMING 2000 BLAZER 4WD 4.3L:
FROM ALLDATA
ASSUMING 2000 BLAZER 4WD 4.3L:
FROM ALLDATA
CIRCUIT DESCRIPTION
The Heated Oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.
Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.
This Diagnostic Trouble Code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the Vehicle Control Module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:
^ An open or a short to voltage on either the HO2S signal or HO2S low circuits
^ A malfunctioning HO2S
^ A problem in the HO2S heater or its circuit
^ A faulty HO2S ground
This DTC determines if the HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below.
^ An open circuit in either the HO2S ignition feed or the HO2S heater ground circuits
^ An HO2S heater element problem
CONDITIONS FOR RUNNING THE DTC
IMPORTANT: This test is void for this cold start if the system voltage remains outside the specified range for more than 4 seconds.
^ The system voltage is between 11.7-17 volts.
^ The MAF is less than 27 g/s.
^ The engine run time is more than 2 seconds.
^ The ECT is less than 33°C (91°F).
^ The IAT is less than 33°C (91°F).
^ The difference between the ECT and IAT is 5°C (9°F) or less.
CONDITIONS FOR SETTING THE DTC
The O2 sensor voltage remains within 150 mV of its startup voltage for 245 seconds after cold start.
ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame and Failure Records.
CONDITIONS FOR CLEARING THE MIL OR DTC
^ The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
^ Use a scan tool in order to clear the DTCs. An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.
The Heated Oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.
Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.
This Diagnostic Trouble Code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the Vehicle Control Module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:
^ An open or a short to voltage on either the HO2S signal or HO2S low circuits
^ A malfunctioning HO2S
^ A problem in the HO2S heater or its circuit
^ A faulty HO2S ground
This DTC determines if the HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below.
^ An open circuit in either the HO2S ignition feed or the HO2S heater ground circuits
^ An HO2S heater element problem
CONDITIONS FOR RUNNING THE DTC
IMPORTANT: This test is void for this cold start if the system voltage remains outside the specified range for more than 4 seconds.
^ The system voltage is between 11.7-17 volts.
^ The MAF is less than 27 g/s.
^ The engine run time is more than 2 seconds.
^ The ECT is less than 33°C (91°F).
^ The IAT is less than 33°C (91°F).
^ The difference between the ECT and IAT is 5°C (9°F) or less.
CONDITIONS FOR SETTING THE DTC
The O2 sensor voltage remains within 150 mV of its startup voltage for 245 seconds after cold start.
ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame and Failure Records.
CONDITIONS FOR CLEARING THE MIL OR DTC
^ The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
^ Use a scan tool in order to clear the DTCs. An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.
#3
12-10-2013, 10:38 AM
Ho2s
Excellent response to my question. The Blazer is a 99'. I suspect all said hold true though. some of this is a bit beyond me right now, but as a former Navy pilot, I appreciate the expertise of those mechanics & engineers that make things work. Thank you!
#6
12-13-2013, 08:22 AM
ALLDATA LLC is a source of automotive OEM information. ALLDATA provides vehicle manufacturers' diagnostic and repair information
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