Standard Models (Non-Alternative Fuels)

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between the Heated Oxygen Sensor (HO2S) high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a Diagnostic Trouble Code (DTC) sets.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404, or P1441 are not set.
^ The air fuel ratio is between 14.5:1 and 14.7:1.
^ The Throttle Position (TP) sensor is between 3-70 percent.
^ The loop status is closed.
^ The ignition 1 signal is between 9-18 volts.
^ The fuel tank level remaining is more than 10 percent.
^ Intrusive tests are not in progress.
^ Scan tool output controls are not active.

CONDITIONS FOR SETTING THE DTC
The HO2S signal voltage remains above 977 mV for 250 seconds.

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

IMPORTANT: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

^ Inspect the HO2S electrical connections for evidence of water intrusion. Water present in the connector causes the B+ supply to the heater to bleed over to the signal circuit.
^ Inspect the fuel pressure. The system goes rich if the pressure is too high. The PCM compensates for some increase. If the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ Inspect for a rich injector. 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
^ Inspect for a leaking injector. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ Inspect the fuel pressure regulator. Inspect the vacuum line going to the fuel pressure regulator for evidence of fuel. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ Inspect the Evaporative Emissions (EVAP) canister purge. Inspect the canister for fuel saturation. If the canister is full of fuel, check the canister control and the hoses. Refer to Evaporative Emission (EVAP) Control System Description.
^ Inspect the Mass Air Flow (MAF) sensor. Disconnect the MAF sensor and see if the rich condition is corrected. If the condition is corrected, check for proper installation. If the sensor is correctly installed, replace the sensor. If the sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows cast that indicate the proper air flow direction. The arrows must point toward the engine.
^ Inspect the HO2S wires. An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or for contamination. Refer to Heated Oxygen Sensor (HO2S) Wiring Repairs in Diagrams.
^ Inspect the TP sensor. An intermittent TP sensor output causes the system to go rich, due to a false indication of the engine accelerating. For an intermittent condition, refer to Symptoms Computers and Control Systems. Standard Model (Non-Alternative Fuels)

TEST DESCRIPTION

Steps 1-5:

Steps 6-12:

The numbers below refer to the step numbers on the diagnostic table.
2. If the voltage is above the specified value the condition is present.
4. Jumpering the HO2S low signal circuit to ground is necessary for the PCM to correctly measure the voltage on the HO2S high signal circuit. If the HO2S voltage is within the specified range, the PCM and HO2S high signal circuit are OK.