P0147
DTC P0147 HO2S Heater Performance Bank 1 Sensor 3
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 controls module (PCM/VCM) supplies the HO2S with signal High and Low circuits. Ignition voltage and ground is 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 and maintain the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. Once the HO2S has reached operating temperature, the controls module monitors the HO2S bias, or reference, voltage as well as the HO2S signal voltage for closed loop fuel control. During normal closed loop fuel control operation, the controls module will add fuel (enriches the mixture) when the HO2S detects a lean exhaust content and subtract fuel (leans-out the mixture) when the HO2S detects a rich exhaust condition.
Certain vehicle models utilize an oxygen sensor after the catalyst converter in order to monitor catalyst efficiency.
This DTC determines if the HO2S is functioning properly by checking for an adequate number of HO2S voltage transitions above and below the bias range of 300 - 600 mV. This DTC sets when the 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 listed below.
- 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 poor 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's Freeze Frame and Failure Records.
Conditions for Clearing the MIL/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 the scan tool Clear Information function
Diagnostic Aids
Important: Never solder the HO2S wires. For proper wire and connection repair refer to Wiring Repairs or Connector Repairs.
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 check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs.
Steps 1 - 2:
Steps 3 - 4:
Steps 5 - 8:
Steps 9 - 13:
Steps 14 - 15:
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF the exhaust usually contains a high oxygen content. With the engine OFF the HO2S voltage will usually decrease from the initial (bias) voltage due to the high oxygen content.
4. This step checks for proper HO2S heater ignition feed and ground supply.
5. This step checks for proper VCM and signal circuit operation.