Circuit Description
Heated oxygen sensors (HO2S) are used in order to minimize the amount of time required for Closed Loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor (O2S) heater greatly decreases the amount of time required for the pre-catalyst oxygen sensors to become active. An O2S heater is required by catalyst monitor sensor to maintain a sufficiently high temperature which allows accurate exhaust oxygen content readings further from the engine. The powertrain control module (PCM) will run the heater test only after a cold start, and only once during an ignition cycle. The cold start is determined by engine coolant temperature (ECT) and intake air temperature (IAT) at the time of startup. When the engine is started the PCM will monitor the HO2S voltage. When the post HO2S voltage indicates a sufficiently active sensor, the PCM looks at how much time has elapsed since startup. If the PCM determines that too much time was required for the post HO2S to become active, this diagnostic trouble code (DTC) will set. The time the HO2S should reach operating temperature is based on the ECT at start-up and the average mass air flow (MAF) since startup. The higher average airflow, or the higher startup ECT equals a shorter time to HO2S activity.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set. |
| • | The system voltage is between 9-18 volts. |
| • | The intake air temperature (IAT) is less than 35°C (95°F) at start-up. |
| • | The engine coolant temperature (ECT) is less than 35°C (95°F) at start-up. |
| • | The IAT and the ECT are within 6°C (11°F) of each other at start-up. |
| • | The average mass air flow (MAF) for the sample period is less than 22.7 g/s. |
Conditions for Setting the DTC
| • | The post-HO2S voltage remains within 150 mV of the bias voltage, about 450 mV. |
| • | The amount of time depends on engine coolant temperature at start-up, and on the average air flow since start-up. |
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
If the condition is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The HO2S should be allowed to cool before performing this test. If the HO2S heater is functioning, the signal voltage will gradually increase or decrease as the sensor element warms. If the heater is not functioning, the HO2S signal will remain near the 450 mV bias voltage.
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This step ensures that the ignition 1 voltage circuit to the HO2S is not open or shorted. The test lamp should be connected to a good chassis ground, in case the HO2S low signal or HO2S heater ground circuit is poor.
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This step tests the HO2S heater ground circuit.
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This step tests for an open or shorted HO2S heater element. The heater element resistance will vary according to HO2S temperature. A hot HO2S heater element will measure a much higher resistance than a HO2S heater element at room temperature. Allow the HO2S to cool before measuring HO2S heater element resistance.
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An open HO2S high signal or low signal circuit can cause the HO2S heater to appear faulty. inspect these circuits before replacing the sensor.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
|
Important: If engine has just been operating, allow engine to cool for about one half hour before proceeding.
Does HO2S voltage vary from bias voltage to more than the first specified value or less than the second specified value? | 600 mV 300 mV | Go to Intermittent Conditions | Go to Step 3 | |
3 | Inspect ignition fuse for the HO2S 2 ignition 1 voltage circuit. Is the fuse open? | -- | Go to Step 15 | Go to Step 4 |
|
Important: Use a known good ground. Do not use the HO2S heater ground circuit or the HO2S low signal circuit.
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Connect a test lamp between HO2S ignition 1 voltage and HO2S heater ground. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 8 | |
Does the resistance measure within the specified range? | 5-10 ohms | Go to Step 9 | Go to Step 14 | |
7 | Repair the open HO2S ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
8 | Repair open HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
9 | Inspect for poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 10 |
10 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 11 |
Inspect for a poor HO2S high signal or low signal circuit connection at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 | |
12 | Inspect for a poor HO2S low signal circuit connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 |
13 | Inspect for a poor HO2S high signal circuit connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 |
14 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 16 | -- |
15 | Repair the short to ground in HO2S ignition 1 voltage circuit and replace the faulty fuse. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
16 |
Does the DTC run and pass? | -- | Go to Step 17 | Go to Step 2 |
17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
