W/Case Grounded HO2S

CIRCUIT DESCRIPTION
This 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 bias voltage of approximately 450 mV on the HO2S signal high and low circuits. When you turn the ignition to the ON position, battery voltage is supplied to the HO2S heater. As the heater reaches the operating temperature, the HO2S voltage responds by changing from a bias voltage range to the normal operation. Typically, as the HO2S reaches the operating temperature, the HO2S voltage goes from a bias voltage to a voltage below 300 mV. Depending on the exhaust gas content, the HO2S voltage may possibly go above 450 mV.

The PCM runs the heater test only on a cold start, depending on the cumulative air flow, and only once an ignition cycle. When you start the engine the PCM monitors the H023 voltage. When the HO2S voltage goes above or below the bias range threshold, the PCM determines how much time elapsed. If the PCM detects that the process took too much time for the HO2S to enter into normal operating range, a DTC sets. The time the process takes the HO2S to reach operating temperature is based on the amount of air that flows into the engine.

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 HO2S voltage is between 425-475 mV at engine start-up.
^ The intake air temperature (IAT) and the engine coolant temperature (ECT) are less than 50°C (122°F) and are within 8°C (14.5°F) of each other at engine start-up.
^ The ignition 1 signal is between 9-18 volts.
^ Intrusive tests are not in progress.
^ The scan tool output controls are not active.
^ The mass air flow (MAF) is less than 32 g/s.

CONDITIONS FOR SETTING THE DTC
The HO2S voltage remains within 75 mV of the start-up voltage for a predetermined amount of time, based on ECT and air flow.

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.

^ Using the Freeze Frame/Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records can help determine how many kilometers (miles) since the DTC set. The fail counter and pass counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. In order to isolate when the DTC failed, operate vehicle within the same Freeze Frame conditions that you observed:
- The RPM
- The vehicle load
- The vehicle speed
- The temperature

For an intermittent condition, refer to Intermittent Conditions. Diagnostic Aids
^ The heater diagnostic will only run on a cold start and run once per ignition cycle.
^ 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 contamination. Refer to Heated Oxygen Sensor (HO2S) Wiring Repairs in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-8:

Steps 9-13:

The numbers below refer to the step numbers on the diagnostic table.
2. Allow the engine to cool before performing this test. If the sensor is at the operating temperature, the HO2S voltage will stay high or low. If the HO2S voltage stays between 300-600 mV this indicates the HO2S heater is inoperative.
3. If more than one HO2S DTC is set, this is a good indication that the HO2S fuse is open. Test all the related circuits going to all the HO2S for a short to ground. If you cannot locate a shorted circuit, you may need to disconnect each HO2S one at a time to locate a shorted sensor.
4. This step determines if an ignition positive voltage supply is available at the sensor.
5. This step determines if a ground is available at the sensor.
6. This step determines if the HO2S heater element is internally open.
7. Inspect the ignition positive voltage circuits at the underhood electrical center for poor connections.
8. Test the ground circuits for an open if more then one heater DTC sets.