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. This DTC will set if the HO2S 1 voltage remains above a calibrated amount for an excessive amount of time.
Each HO2S has the following circuits:
| • | HO2S 1 high signal |
| • | HO2S 1 low signal |
| • | HO2S 1 heater ignition 1 voltage |
| • | HO2S 1 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 system voltage is between 9-18 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 55 seconds:
| • | The HO2S 1 signal voltage remains above 975 mV during Closed Loop operation. |
| • | The HO2S 1 signal voltage remains above 200 mV during decel fuel cut-off (DFCO) operation. |
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 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. |
| • | 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 1 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 1 voltage signal will fluctuate above and below the bias voltage amount.
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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 | |||||||||||||||||||||||||||||
Does the HO2S 1 voltage remain above the specified value? | 975 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 more than the amount specified? | 975 mV | Go to Step 5 | Go to Step 9 | |||||||||||||||||||||||||||||
5 |
Is the voltage more than the amount specified? | 5.5 V | Go to Step 7 | Go to Step 6 | ||||||||||||||||||||||||||||
6 |
Do any 5-volt reference circuit DTCs set? | -- | Go to Step 8 | Go to Step 7 | ||||||||||||||||||||||||||||
7 |
Important: Disconnection of the PCM during testing may eliminate the voltage source that caused this fault. Test the HO2S 1 high signal circuit for a short to voltage. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||||||||||||||||||||||||
8 |
Important: Disconnection of the PCM during testing may eliminate the voltage source that caused the fault. Test the HO2S 1 high signal circuit for a short to the affected 5-volt reference circuit. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||||||||||||||||||||||||
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 14 | Go to Step 10 | |||||||||||||||||||||||||||||
10 | Before continuing, inspect for poor connections at the HO2S 1 connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||||||||||||||||||||||||||
11 | Inspect for poor connections at the powertrain control module (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 14 | Go to Step 12 | ||||||||||||||||||||||||||||
12 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||||||||||||||||||||
13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||||||||||||||||||||
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 | ||||||||||||||||||||||||||||
15 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||||||||||||||
