Circuit Description
Heated oxygen sensors (HO2S) are used in order to minimize the time required for closed loop fuel control operation, and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the time required for HO2S 1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S 2 in order to maintain a sufficiently high temperature. This 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, determined by the engine coolant temperature and the intake air temperature at the time of start-up, and only once during an ignition cycle. When the engine is started, the PCM will monitor the HO2S voltage. When the HO2S voltage indicates a sufficiently active sensor, the PCM looks at how much time has elapsed since start-up. The time necessary take the HO2S to reach the operating temperature is based on the engine coolant temperature at start-up and the average mass air flow since startup. A higher average airflow or a higher startup engine coolant temperature equals a shorter time to HO2S activity. If the PCM determines that too much time was required for the HO2S 1 to become active, DTC P0135 will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set. |
| • | The engine run time is more than 3 seconds. |
| • | The system voltage is between 9-16 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. |
| • | For VIN K, the average mass airflow for the sample period is less than 18 g/s. |
| • | For VIN 1, the average mass airflow for the sample period is less than 21 g/s. |
Conditions for Setting the DTC
The HO2S 1 voltage remains within 150 mV of the bias voltage of approximately 450 mV, for a longer time than necessary. The time ranges between 50-85 seconds and depends on the engine coolant temperature at start-up and on the average MAF 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. |
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 you perform 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 the event that the HO2S low signal circuit or the HO2S heater ground circuit is malfunctioning.
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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.
Important:: 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 DTC to set with the HO2S heater operating normally. Test the HO2S high and low signal 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 the engine has just been operating, allow engine to cool for 1/2 hour before proceeding.
Does HO2S voltage go from bias voltage to more than the first specified value, or to less than the second specified value within 2 minutes? | 600 mV 300 mV | Go to Intermittent Conditions | Go to Step 3 | |
3 | Inspect the fuse for the HO2S 1 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 1 heater ground circuit or the HO2S 1 low signal circuit. Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Connect the test lamp between the HO2S 1 ignition 1 voltage circuit and the HO2S 1 heater ground circuit. Does test lamp illuminate? | -- | Go to Step 6 | Go to Step 8 | |
Does the resistance measure within the specified values? | 4-6 Ohms | Go to Step 9 | Go to | |
7 | Repair open in the HO2S 1 ignition 1 voltage circuit to HO2S 1. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
8 | Repair open in the HO2S 1 heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
9 |
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 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 | |
12 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 |
13 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 |
14 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
15 | Locate and repair short to ground in HO2S 1 or HO2S 2 ignition 1 voltage circuits and replace the 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 in Capture Info. Does the scan tool display any DTCs that have not been diagnosed? | -- | System OK | |
