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 |
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 intrusive tests (i.e., EGR or Catalyst) in progress |
| • | No device control active |
| • | The system voltage is between 11.7-18 volts. |
| • | The engine run time is more than 2 minutes. |
| • | DFCO mode is not active |
| • | The ECT is 58°C (137°F) or more. |
| • | The MAF is 13 g/s or more. |
| • | 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 110 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 Freeze Frame/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. |
Diagnostic Aids
Important: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs in Wiring Systems.
Check for the following conditions:
| • | 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. If the test lamp lights, replace the HO2S. |
| • | 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 inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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HO2S contamination is indicated if multiple Response, Switching or Time Ratio HO2S DTCs are set.
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The use of leaded fuel may be indicated by the removal or tampering of the fuel filler restrictor.
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine.
If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
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Even small exhaust leaks can cause slow response from the HO2S.
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An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
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If the voltage observed in step 8 is less than the range specified, a short between the HIGH and LOW circuits or a short between the HIGH circuit and ground is indicated. With the HO2S and the VCM disconnected, the resistance between the HIGH and LOW circuits and the resistance between the HIGH circuit and ground should measure infinite.
If the voltage observed in step 8 is more than the range specified, a short between the HIGH circuit and an ignition voltage source is indicated.
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If the voltage observed in step 9 is not below the voltage specified, a high resistance (open) HIGH or LOW circuit is indicated.
Good circuit continuity measures less than 5 ohms with the VCM and sensor disconnected. Measure between the VCM connector and the HO2S connector. Ensure VCM terminal contact is good.
Step | Action | Values | Yes | No | ||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||||||||||||||||||||
In addition to this DTC, check for the following HO2S DTCs:
Are any of the above listed heated oxygen sensor DTCs set? | -- | |||||||||||||||||||||||||||||||||||
3 | Are any powertrain component DTCs set? | -- | Go to DTCs that are set | |||||||||||||||||||||||||||||||||
Important: The contamination source must be removed prior to operating the engine with the replacement sensors. Has the contamination source been removed and the affected sensors replaced? | -- | -- | ||||||||||||||||||||||||||||||||||
5 |
Did this DTC run and fail this ignition? | -- | ||||||||||||||||||||||||||||||||||
6 |
Did you find a problem? | -- | Go to Diagnostic Aids | |||||||||||||||||||||||||||||||||
Did you find and repair a problem? | -- | |||||||||||||||||||||||||||||||||||
8 |
Is the HO2S voltage within the value range specified? | 351 to 551 mV | ||||||||||||||||||||||||||||||||||
9 |
Is the HO2S voltage less than the value specified? | 20 mV | ||||||||||||||||||||||||||||||||||
10 |
Is the test lamp ON? | -- | ||||||||||||||||||||||||||||||||||
11 | Connect the test lamp between the HO2S heater ignition feed circuit terminal and the HO2S heater ground circuit terminal, both on engine harness side. Is the test lamp ON? | -- | ||||||||||||||||||||||||||||||||||
HO2S contamination sources include the following:
Is the action complete? | -- | -- | ||||||||||||||||||||||||||||||||||
Repair the short between the HO2S HIGH and LOW circuits or between the HO2S HIGH signal circuit and an ignition voltage source. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | ||||||||||||||||||||||||||||||||||
Is the action complete? | -- | -- | ||||||||||||||||||||||||||||||||||
15 | Repair the HO2S heater ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||||||||||||||||||||||
16 | Repair the HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||||||||||||||||||||||
17 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||||||||||||||||||||||||||
18 |
Did this DTC run and pass this ignition? | -- | System OK |
