P0158

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 the 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 the operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module 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 the catalyst efficiency.

This DTC is designed to detect an HO2S voltage that remains high for more than 100 seconds during a 120-second test period. This DTC is set during the following conditions:
^ An HO2S circuit results in a false rich exhaust condition.
^ The HO2S is correctly detecting the lean air/fuel ratio resulting from either a vacuum leak or from a fuel control system problem.

CONDITIONS FOR RUNNING THE DTC
Criteria 1
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P01 13, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set.
^ The Secondary Air Injection (AIR) and the Exhaust Gas Recirculation (EGR) diagnostics are not active.
^ The ignition voltage is more than 9 volts.
^ The fuel system is operating in Closed Loop.
^ The Accelerator Pedal Position (APP) indicated angle is between 3-50 percent.
^ The fuel level is above 10 percent.

Or

Criteria 2
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set.
^ The Secondary Air Injection (AIR) and the Exhaust Gas Recirculation (EGR) diagnostics are not active.
^ The ignition voltage is more than 9 volts.
^ The fuel system is operating in Closed Loop.
^ The fuel level is above 10 percent.
^ The Decel Fuel Cut Off mode is enabled for more than 3 seconds.

CONDITIONS FOR SETTING THE DTC
Criteria 1
^ The HO2S signal voltage remains above 994 mV.
^ The Criteria 1 conditions are present for 200 seconds.

OR

Criteria 2
^ The HO2S signal voltage remains above 469 mV for 4.5 seconds.
^ The Criteria 2 conditions are present for 5 seconds during the Deceleration Fuel Cut-off mode.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
^ Inspect the following components and Systems:
- Check the HO2S electrical connections for evidence of water intrusion. Water in the connector causes the ignition 1 voltage supply to the heater to bleed over to the signal circuit.
- Fuel pressure-The system goes rich if the pressure is too high. The PCM compensates for some increase. However, if the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
- Rich injectors-Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool. Component Tests and General Diagnostics Component Tests and General Diagnostics
- Leaking injector-Refer to the Fuel System Diagnosis. Component Tests and General Diagnostics
- Fuel pressure regulator-Inspect the vacuum line going to the fuel pressure regulator for evidence of fuel. Refer to the Fuel System Diagnosis. Component Tests and General Diagnostics
- Evaporative Emissions (EVAP) canister purge-Check the canister for fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission (EVAP) Control System Description.
- MAF sensor-Disconnect the MAF sensor and see if the rich condition is corrected. If so, check for proper installation. If installed correctly, replace the MAF sensor. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows indicating proper air flow direction. The arrows must point toward the engine.
- An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provides the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor (HO2S) Wiring Repairs in Diagrams.
- TP sensor-An intermittent TP sensor output causes the system to go rich, due to a false indication of the engine accelerating.
^ Use the Freeze Frame/Failure Records data in order to locate an intermittent condition in the following ways:
- If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in determining how many miles since the DTC set.
- The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail.
- Operate the vehicle within the same Freeze Frame conditions that you observed in order to isolate when the DTC failed. Use the following conditions for your tests:
^ The RPM
^ The load
^ The vehicle speed
^ The temperature
^ For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-6:

Steps 7-13:

The number below refers to the step number on the diagnostic table.
5. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank