Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 3 voltage circuit through a fuse. Ground is provide to the heater by a ground circuit. This diagnostic will only run once per ignition cycle. If the PCM detects that the HO2S time to become active was too long, DTC P0135, P0141, P0155 or P0161 sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0131, P0132, P0134, P0137, P0138, P0140, P0151, P0152, P0154, P0157, P0158, P0160, P0200, P0300, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1221, P1258, P1415, P1416, P1441, P1514, P1515, P1516, P1517, or P1518 are not set. |
| • | The IAT sensor parameter and the ECT sensor parameter are less than 50°C (122°F) and are within 8°C (14.5°F) of each other at engine start-up. |
| • | The affected HO2S voltage parameter is between 425-475 mV at engine start-up. |
| • | The Ignition 1 Signal parameter is between 9-18 volts. |
| • | The MAF sensor parameter is less than 21 g/s. |
Conditions for Setting the DTC
The affected HO2S voltage parameter is within 150 mV of the start-up voltage for a predetermined amount of time, based on the engine coolant temperature and the 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Allow the engine to cool before you perform this test. If the HO2S voltage stays between 300-600 mV, the HO2S heater is inoperative.
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If more than one HO2S DTC is set, this is a good indication that the HO2S fuse is open. Test all the related circuits that go to all the heated oxygen sensors for a short to ground. If all the wiring is OK, you may need to disconnect each HO2S one at a time in order to locate a shorted sensor.
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This verifies whether B+ supply is available at the sensor.
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This step verifies whether a ground is available at the sensor.
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This step determines whether the HO2S heater element is internally open.
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Inspect the ignition feed circuits at the underhood electrical center for proper connections.
-
Inspect the splice pack for the ground circuits for an open circuit. A condition at the splice pack sets more than one heater DTC.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
|
Important: Allow the engine to cool for 1/2 hour before proceeding with this table. Important: If DTC P0300 is set, diagnose that DTC first. Refer to Diagnostic Trouble Code (DTC) List .
Does the HO2S voltage go from a bias voltage to above or below the specified range? | 300-600 mV | Go to Intermittent Conditions | Go to Step 3 | |
Inspect the HO2S fuse for an open. Is the HO2S fuse open? | -- | Go to Step 11 | Go to Step 4 | |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Connect the test lamp between the HO2S ignition 3 voltage and the HO2S heater ground. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 8 | |
Measure the resistance between the HO2S ignition 3 voltage and the HO2S heater ground at the HO2S sensor side with the DMM. Is the HO2S resistance within the specified range? | 2-50 ohms | Go to Step 9 | Go to Step 10 | |
Repair the open in the HO2S ignition 3 voltage circuit to the HO2S. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 12 | -- | |
Repair the open in the HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 12 | -- | |
9 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
10 | Replace the affected HO2S that has been diagnosed. Refer to: Did you complete the replacement? | -- | Go to Step 12 | -- |
11 |
Did you complete the repair? | -- | Go to Step 12 | -- |
12 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
