Circuit Description
Heated oxygen sensors (HO2S) are used to minimize the amount of time required for Closed Loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of time required for fuel control sensor HO2S 1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S 2 to maintain a sufficiently high temperature. This allows accurate exhaust oxygen content readings farther from the engine.
The powertrain control module (PCM) will run the heater test only after a cold start (determined by engine coolant and intake air temperature at the time of startup) 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 startup. If the PCM determines that too much time was required for the HO2S 1 to become active, a diagnostic trouble code (DTC) P0135 will set. The time needed for the HO2S to reach operating temperature is based on the engine coolant temperature (ECT) at start-up and the average mass air flow (MAF) since startup (higher average airflow or higher startup engine coolant temperature = 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 9-16 volts |
| • | The intake air temperature (IAT) is less than 2°C (35°F) at startup |
| • | The engine coolant temperature (ECT) is less than 2°C (35°F) at startup |
| • | The IAT and ECT are within 6°C (11°F) of each other at start-up |
| • | VIN K - Average mass air flow for the sample period is less than 20 g/s |
| VIN 1 - Average mass air flow for the sample period is less than 19 g/s |
Conditions for Setting the DTC
HO2S 1 voltage remains within 150 mV of the bias voltage (about 450 mV) for a longer amount of time than it should. The amount of time ranges between 50-80 seconds depending on engine coolant temperature at startup and average mass air flow since startup.
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 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 ground, in case the HO2S low signal or HO2S heater ground circuit is malfunctioning.
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This step checks the HO2S heater ground circuit.
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This step checks for an open or shorted HO2S heater element.
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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. Check the HO2S high signal and the HO2S low signal circuits before replacing the sensor.
Step | Action | Value(s) | 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 the engine to cool for about one half hour or until bias voltage is observed on the scan tool before proceeding.
Does HO2S voltage go from bias voltage to more than the first specified value or 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 | |
Important: The heater element resistance will vary according to HO2S temperature (a hot HO2S heater element will measure a much higher resistance than an HO2S heater element at room temperature). Allow the HO2S to cool before measuring HO2S heater element resistance. Does the resistance measure within the specified values? | 5-6 ohms | Go to Step 9 | Go to Step 14 | |
7 | Repair open 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 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 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 either HO2S ignition 1 voltage circuit and replace the fuse. Refer to Testing for Continuity , Testing for Intermittent Conditions and Poor Connections , Repairing Connector Terminals , Connector Repairs , and 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 | |
