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 is designed in order to detect an HO2S that is slow to respond to changes in the exhaust oxygen content.
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 11.7-18 volts. |
| • | DTCs P0151, P0152, P0154, and P0155 not active |
| • | The system is in closed loop. |
| • | The ECT is more than 57°C (135°F). |
| • | The engine run time is more than 75 seconds. |
| • | The MAF is between 15-55 g/s. |
| • | The engine speed is between 1100-3000 RPM. |
| • | The EVAP canister purge duty cycle is more than 0 percent. |
| • | The above conditions present for more than 2 seconds |
Conditions for Setting the DTC
| • | The time since closed loop mode enabled is more than 100 seconds. |
| • | The average lean-to-rich response time (from below 300 mV to above 600 mV) is more than 125 ms. |
| • | The average rich-to-lean response time (from above 600 mV to below 300 mV) is more than 125 ms. |
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 connector repairs, refer to Wiring Repairs in Wiring Systems.
Check for the following conditions:
| • | An improperly installed air cleaner outlet duct |
| • | The air cleaner outlet duct for a collapsed duct, restrictions, or a missing or plugged air filter |
| • | Throttle body and intake manifold vacuum leaks |
| • | 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 numbers below refer to the step numbers on the diagnostic table.
-
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.
-
This step checks the VCM and the HIGH and LOW circuits between the VCM and the HO2S connector for proper operation.
-
This step checks for proper HO2S heater circuit operation up to the HO2S connector.
Step | Action | Values | Yes | No | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||||||
Is the HO2S voltage fixed within the voltage range specified? | 399-473 mV | |||||||||||||||||||||
3 |
Did you find a problem? | -- | Go to Diagnostic Aids | |||||||||||||||||||
Is the voltage less than the specified value? | 20 mV | |||||||||||||||||||||
5 |
Is the resistance of both circuits less than the specified value? | 5 ohms | ||||||||||||||||||||
6 |
Did you find a problem? | -- | ||||||||||||||||||||
Is the test lamp ON? | -- | |||||||||||||||||||||
8 |
Is the action complete? | -- | -- | |||||||||||||||||||
9 |
The leak may be very small and typically be within 30 cm (12 in) of the suspect HO2S. Did you find a problem? | -- | ||||||||||||||||||||
10 | Inspect one of the following that may cause the reference voltage to be skewed:
Is the action complete? | -- | -- | |||||||||||||||||||
11 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||||||||
12 |
Is the resistance less than the specified value? | 500 ohms | ||||||||||||||||||||
13 | Replace the HO2S sensor. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||||||||||||
14 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |||||||||||||||||||
15 |
Does the scan tool indicate the diagnostic Passed? | -- | ||||||||||||||||||||
16 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
