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P0146

DTC P0146 HO2S Circuit Insufficient Activity 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 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 circuit 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

Conditions for Running the DTC
- No active TP sensor DTCs
- No active EVAP system DTCs
- No active IAT sensor DTCs
- No active MAP sensor DTCs
- No active ECT sensor DTCs
- No active MAF sensor DTCs
- No active misfire DTCs
- No intrusive test in progress
- No device controls active
- The system voltage is between 11.7 - 17 volts
- The engine has been running for more than 2 minutes
- O2 Sensor Temperature Test:
- The decel fuel cut-off mode (DFCO) is not active
- The ECT is more than 58.5° C (137° F)
- The MAF is more than 13 g/s
- O2 Sensor Open Test Enable:
- O2 sensor temperature test equals true
- DTC P0147 not active
- The system is in closed loop

Conditions for Setting the DTC
The O2 sensor voltage is between 399 - 473 mV for more than 100 seconds.

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.

Check for the following conditions:
An exhaust system leak (typically within 30 cm (12 in) up-stream of the HO2S).

A malfunctioning HO2S heater or heater circuit
With the ignition ON and the engine OFF, the HO2S voltage displayed on a scan tool should gradually drop to below 0.150 volt, indicating that the heater works properly. If not, disconnect the HO2S and connect a test lamp between the terminals C and D. If the test lamp does not light, repair the open in the HO2S ground circuit or the HO2S ignition feed circuit.

The Intermittent test
Use a scan tool in order to monitor this HO2S signal voltage. Move the related connectors and the wiring harness with a warm engine running at part throttle in Closed Loop. If the failure is induced, the HO2S signal voltage reading changes from its normal fluctuating voltage (above 600 mV and below 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction.
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.

Step 1:




Steps 2 - 4:




Steps 5 - 7:




Steps 8 - 10:




Steps 11 - 13:




Steps 14 - 16:




Steps 17 - 18:




Test Description
The numbers below refer to the step numbers on the diagnostic table
2. This step checks for proper sensor activity. When in Closed Loop fuel control the HO2S voltage should rapidly swing above and below the bias voltage.
4. This step checks the VCM and the HIGH and LOW circuits between the VCM and the HO2S connector for proper operation.
7. This step checks for proper HO2S heater circuit operation up to the HO2S connector.
8. This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground.
13. This step checks for proper circuit resistance between the HO2S LOW circuit and the VCM ground with a cold sensor. A loose HO2S or poor tread to exhaust electrical contact will cause higher resistance when the HO2S is cold. Although 500 ohms is allowed, typical resistance should be less than 50 ohms.
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