W/Case Grounded HO2S
CIRCUIT DESCRIPTIONThis diagnostic applies only to vehicles built with case grounded heated oxygen sensors (HO2S). To identify the HO2S, refer to Computers and Controls Systems Component Views.
The powertrain control module (PCM) supplies a voltage of about 450 mV between the 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, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.
^ The vehicle is operating in Closed Loop.
^ 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.
^ The scan tool output controls are not active.
Rich Test Enable:
^ The air fuel ratio is between 14.5:1-14.7:1.
^ For vehicles with throttle-actuated control (TAC), the throttle position (TP) indicated angle is between 3-70 percent more than the value observed at idle.
^ For vehicles without TAC, the TP is between 3-70 percent.
Decel Fuel Cut-off Test Enable:
^ Decel fuel cut-off (DFCO) is active.
^ The above condition is met for 3 second.
CONDITIONS FOR SETTING THE DTC
Rich Test
The HO2S voltage is more than 930 mV for 200 seconds.
Decel Fuel Cut-off Test
The HO2S voltage is more than 480 mV for 5 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.
^ Clear the MIL and the DTC with a scan tool.
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.
^ 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. Testing and Inspection
^ Leaking injector-Refer to the Fuel System Diagnosis. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool.
^ 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.
^ Mass air flow (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 in the casting 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 Diagnostic Aids.
^ Throttle position (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 Intermittent Conditions.
TEST DESCRIPTION
Steps 1-5:
Steps 6-13:
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.
5. 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.