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 is used for post catalyst monitoring. This DTC will set if the HO2S 2 voltage remains below a calibrated amount for an excessive amount of time.
The HO2S 2 has the following circuits:
| • | HO2S 2 high signal |
| • | HO2S 2 low signal |
| • | HO2S 2 heater ignition 1 voltage |
| • | HO2S 2 heater ground |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, 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 ignition voltage is more than 9 volts and less than 18 volts. |
| • | The system is in Closed Loop. |
| • | The throttle angle is between 5-40 percent. |
Conditions for Setting the DTC
The DTC will set if either of the following conditions are present for up to 5 minutes:
| • | The HO2S 2 signal voltage remains below 30 mV during Closed Loop operation. |
| • | The HO2S 2 signal voltage remains below 600 mV during power enrichment (PE) mode. |
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 after 3 consecutive ignition cycles that the diagnostic runs and passes. |
| • | A current DTC, Last Test Failed, 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. |
| • | Use the scan tool in order 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 voltage may default to the bias voltage. The DTC should be cleared and the Freeze Frame/Failure Records data recorded before proceeding. A normally functioning HO2S 2 voltage signal will fluctuate above and below the bias voltage amount. The action in the test step should result in a visible reaction from the HO2S 2 output.
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A voltage reading other than bias voltage in this step indicates a short circuit condition in the high signal circuit.
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The conditions listed in the table may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.
Step | Action | Values | Yes | No | ||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||||||||
Did the HO2S 2 voltage remain below the specified value? | 30 mV | Go to Step 4 | Go to Step 3 | |||||||||||||||||||||||||||
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||||||||||||||
Does the HO2S voltage read less than the amount specified? | 30 mV | Go to Step 5 | Go to Step 7 | |||||||||||||||||||||||||||
5 | Test the HO2S 2 high signal circuit for a short to ground. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 6 | ||||||||||||||||||||||||||
6 | Test the HO2S 2 low signal circuit for an open or high resistance condition. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||||||||||||||||||||
Before continuing, inspect for the following conditions that may affect the HO2S operation: Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.
Notice: Do not remove the pigtail from either the heated oxygen sensor (HO2S) or the oxygen sensor (O2S). Removing the pigtail or the connector will affect sensor operation. Handle the oxygen sensor carefully. Do not drop the HO2S. Keep the in-line electrical connector and the louvered end free of grease, dirt, or other contaminants. Do not use cleaning solvents of any type. Do not repair the wiring, connector or terminals. Replace the oxygen sensor if the pigtail wiring, connector, or terminal is damaged. This external clean air reference is obtained by way of the oxygen sensor signal and heater wires. Any attempt to repair the wires, connectors, or terminals could result in the obstruction of the air reference and degraded sensor performance. The following guidelines should be used when servicing the heated oxygen sensor:
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | |||||||||||||||||||||||||||
8 | 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 12 | Go to Step 10 | ||||||||||||||||||||||||||
9 | Inspect for poor connections at the PCM harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||||||||||||||||||||
10 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||||||||||||||
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||||||||||||||||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||||||||||||
