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 of the exhaust stream. When the vehicle is first started the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 2 heater performance diagnostic will only run from a cold start and only once per key cycle. This DTC will set if the HO2S 2 heater takes too long to heat based on the HO2S 2 signal voltage input to the PCM. The HO2S 2 heater circuit is energized anytime the ignition key is in the ON position. The HO2S 2 has the following circuits:
| • | HO2S 2 high signal |
| • | HO2S 2 low signal |
| • | HO2S 2 heater ignition voltage |
| • | HO2S 2 heater ground |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, 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 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. |
Conditions for Setting the DTC
HO2S 2 voltage remains within 150 mV of the bias voltage about 450 mV for a longer amount of time. The amount of time ranges between 100-130 seconds depending on ECT at startup and average mass air flow (MAF) since startup.
Action Taken When the DTC Sets
The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the DTC
| • | The PCM turns OFF the MIL lamp after 3 consecutive ignition cycles that the diagnostic runs and passes. |
| • | A current, DTC last test fails, clears when the diagnostic runs and passes. |
| • | A DTC stored in history clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | A scan tool can be used to clear the DTC. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The HO2S 2 should be allowed to cool before performing this test. The HO2S 2 is cool enough if the voltage output is stable at bias or about 450 mV. If the HO2S 2 heater is functioning, the signal voltage will gradually change as the sensor element warms. If the heater is not functioning, the HO2S 2 signal will remain near the 450 mv bias voltage or show very little activity.
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This step ensures that the ignition voltage circuit to the HO2S 2 is not open or shorted. The test lamp must be connected to a good ground, independent of the HO2S system.
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This test must not be performed until the HO2S 2 heater has cooled and stabilized for at least 15 minutes. Heater resistance is typically about 5 ohms at room temperature.
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 engine to cool until near bias voltage is observed on the scan tool before proceeding.
Does the HO2S 2 voltage go to above or below the previously stabilized voltage, by at least as much as the specified value within 2 minutes? | 100 mV | Go to Step 3 | Go to Step 4 | |
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
|
Important: The test lamp must be connected to a good ground
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
5 |
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 10 |
|
Important: The heater element resistance will vary according to HO2S temperature. A hot HO2S heater element will have a higher resistance than at room temperature.
Is the resistance within the specified range? | 2-20 ohms | -- | Go to Step 11 | |
7 | Test the HO2S 2 heater ignition voltage circuit for an open fuse. Refer to Circuit Testing in Wiring Systems. Did you find an open fuse? | -- | Go to Step 8 | Go to Step 9 |
8 | Locate and repair the short to ground in the HO2S 2 heater ignition voltage circuit and replace the fuse. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | -- |
9 | Repair the open or high resistance condition in the HO2S 2 heater ignition voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | -- |
10 | Repair the open or high resistance condition in the HO2S 2 heater ground circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | -- |
11 | Before continuing, inspect for poor connections at the HO2S 2 connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
12 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 |
14 | With a scan tool observe the stored information Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
