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 to provide an accurate voltage signal. The PCM calculates a transition time ratio rich-to-lean and lean-to-rich HO2S voltage transitions. If the calculated transition time ratio is incorrect this DTC will set.
Each HO2S 1 has the following circuits:
| • | HO2S 1 high signal |
| • | HO2S 1 low reference |
| • | HO2S 1 heater ignition voltage |
| • | HO2S 1 heater low control |
| • | Low reference loop |
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 is in Closed Loop. |
| • | The engine has been running for at least 60 seconds. |
| • | The mass air flow (MAF) is between 13-29 g/s. |
| • | The engine speed is between 1,300-3,000 RPM. |
| • | The throttle angle is between 3-35 percent. |
| • | The system voltage is between 9-18 volts. |
| • | The engine coolant temperature (ECT) is more than 50°C (122°F). |
Conditions for Setting the DTC
The average transition time ratio is not within 0.4-4.2 during a 100 second monitoring period.
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 MIL/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 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 the specified amount in this step indicates an open circuit condition in the high signal circuit or the PCM.
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This step checks the HO2S 1 signal circuits from the HO2S connector and the PCM connectors, including the low reference loop between the PCM connectors.
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This step checks for correct HO2S 1 heater circuit operation up to the HO2S connector. The heater low control is controlled by the PCM. The engine must be running to enable the HO2S heater.
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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 fluctuate rapidly above and below the specified value? | 350-550 mV | Go to Step 3 | Go to Step 4 | |||||||||||||||||||||||
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||||||||||
Is the HO2S voltage within the specified range? | 0.425-0.500 V | Go to Step 5 | Go to Step 6 | |||||||||||||||||||||||
5 |
Does the scan tool display less than the specified amount? | 25 mV | Go to Step 8 | Go to Step 6 | ||||||||||||||||||||||
Is the resistance of each circuit less than the specified value? | 5 ohms | Go to Step 11 | Go to Step 7 | |||||||||||||||||||||||
7 | Repair the circuit that measured a high resistance or an open. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||||||||||||||||
Does the test lamp illuminate? | -- | Go to Step 9 | Go to DTC P0135 | |||||||||||||||||||||||
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 | 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 12 | ||||||||||||||||||||||
11 | 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 14 | Go to Step 13 | ||||||||||||||||||||||
12 | Replace the HO2S 1 sensor. 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 | |||||||||||||||||||||||
