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 difference in transition times from lean to rich or rich to lean has exceeded a maximum ratio. The VCM monitors the time it takes for the HO2S to transition from a rich (above 600 mV) to a lean (below 300 mV) and vice versa. If either of these times is longer than the other by a calibrated ratio, this DTC will set.
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 tests (i.e., EGR or Catalyst) in progress |
| • | No device control in progress |
| • | The system voltage is between 11.7-18 volts. |
| • | DTCs P0151, P0152, P0154, and P0155 not active |
| • | The system is in closed loop. |
| • | The ECT is greater than 57°C (135°F). |
| • | The engine has been running for more than 75 seconds. |
| • | The MAF is between 15-55 g/s. |
| • | The engine speed is between 1100-3000 RPM. |
| • | The EVAP canister purge is active. |
| • | The above conditions are present for more than 2 seconds. |
Conditions for Setting the DTC
The number of lean-to-rich and rich-to-lean transitions within a 100 second sample period were less than a calibrated value.
Action Taken When the DTC Sets
The VCM turns the MIL (Malfunction Indicator Lamp) ON after 2 consecutive test failures.
The VCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records store this information.
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 connector repairs, refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.
Check for the following conditions:
| • | An improperly installed air intake duct. |
| • | The air intake duct for collapsed ducting, restrictions, or a missing or plugged air filter. |
| • | Vacuum leaks in the throttle body and the intake manifold. |
| • | A damaged or blocked throttle body inlet. |
| • | Exhaust system for corrosion, leaks, or loose or missing hardware. Refer to Exhaust System Inspection in Engine Exhaust. |
| • | The HO2S is installed securely and the pigtail harness is not contacting the exhaust manifold or wires. |
| • | HO2S contamination |
| • | The vacuum hoses for splits, kinks, and proper connections. |
| • | Excessive water, alcohol, or other contaminants in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | VCM sensor grounds that are clean, tight, and properly positioned. |
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 number below refers to the step number on the diagnostic table.
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Heated oxygen sensor (HO2S) contamination is indicated if multiple response, switching or time ratio HO2S DTCs are set.
-
Evidence of removal or tampering with the fuel filler restrictor may indicate the use of leaded fuel.
A silicon-contaminated HO2S 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 a un-approved silicon room-temperature vulcanizing (RTV) engine gasket material, or the use of silicon-based sprays or fluids within the engine.
If you do not correct the cause of this contamination, the replacement HO2S will also become contaminated.
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Even small exhaust leaks can cause a slow response from the HO2S.
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A silicon-contaminated HO2S 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 an un-approved silicon room-temperature vulcanizing (RTV) engine gasket material or the use of the use of silicon-based sprays or fluids within the engine. If you do not correct the cause of this contamination, the replacement HO2S will also become contaminated.
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If the voltage observed in step 8 is less than the range specified, it indicates a short between the HIGH and LOW circuits, or a short between the HIGH circuit and ground. If you disconnect the HO2S and the vehicle control monitor (VCM), the resistance between the HIGH and LOW circuits, and the resistance between the HIGH circuit and ground should measure infinite.
If the voltage in step 8 is more than the specified range, it indicates a short between the HIGH circuit and an ignition voltage source.
-
If the voltage in step 9 is not below the specified voltage, it indicates a high resistance HIGH or LOW circuit.
Good circuit continuity measures less than 5 ohms when the VCM and the sensor are disconnected. Measure between the VCM connector and the HO2S connector. Ensure that the 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 HO2S DTCs set? | -- | |||||||||||||||||||||||||||||||||||
3 | Are any powertrain component DTCs set? | -- | Go to the applicable DTC table | |||||||||||||||||||||||||||||||||
Have you removed the contamination source, and have you replaced the affected sensors replaced? | -- | -- | ||||||||||||||||||||||||||||||||||
5 |
Did this DTC run and fail this ignition? | -- | ||||||||||||||||||||||||||||||||||
6 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Did you find a problem? | -- | Go to Diagnostic Aids | |||||||||||||||||||||||||||||||||
Did you find and repair a problem? | -- | |||||||||||||||||||||||||||||||||||
8 |
Is the HO2S voltage within the specified value range? | 351 - 551 mV | ||||||||||||||||||||||||||||||||||
9 |
Is the HO2S voltage less than the specified value? | 20 mV | ||||||||||||||||||||||||||||||||||
10 |
Does the test lamp illuminate? | -- | ||||||||||||||||||||||||||||||||||
11 | Connect the test lamp between the HO2S heater ignition feed circuit terminal on the engine harness side and the HO2S heater ground circuit terminal on the engine harness side. Does the test lamp illuminate? | -- | ||||||||||||||||||||||||||||||||||
HO2S contamination sources include the following:
Is the action complete? | -- | -- | ||||||||||||||||||||||||||||||||||
Is the action complete? | -- | Go to Diagnostic Aids | ||||||||||||||||||||||||||||||||||
Did you find a problem? | -- | -- | ||||||||||||||||||||||||||||||||||
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 |
