Circuit Description
Heated oxygen sensors (HO2S) are used in order to minimize the time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the 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 further from the engine.
The PCM will run the heater test only after a cold start (determined by engine coolant temperature and the intake air temperature at the time of startup) and will test 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 determines how much time has elapsed since startup. If the PCM determines that too much time was required for the HO2S 2 to become active, DTC P0141 will set. The time the HO2S needs to reach the operating temperature is based on the engine coolant temperature at startup and the average mass air flow since start-up. A higher average airflow or higher startup engine coolant temperature means less time to HO2S activity.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0112, P0113, 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 9-18 volts. |
| • | The intake air temperature (IAT) is less than 35°C (95°F) at start-up. |
| • | The engine coolant temperature (ECT) is less than 35°C (95°F) at start-up. |
| • | The intake air temperature (IAT) and the ECT are within 6°C (43°F) of each other at start-up. |
Conditions for Setting the DTC
HO2S 2 voltage remains within 150 mV of the bias voltage, or approximately 450 mV for a longer of time than it should. The time ranges between 100-130 seconds, depending on the engine coolant temperature at startup and on the average 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 chassis ground, in case the HO2S low or HO2S heater ground circuit is malfunctioning.
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Tests the HO2S heater ground circuit.
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Tests for an open or shorted HO2S heater element.
Step | Action | Values | 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 for about one hour before proceeding.
Does the HO2S voltage go from bias voltage to greater 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 fuse for HO2S 2 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 2 heater ground or the low reference circuit. Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Connect test lamp between the HO2S 2 ignition 1 voltage circuit and the HO2S 2 heater ground. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 8 | |
Does the resistance measure within the specified values? | 4-6 ohms | Go to Step 9 | Go to Step 14 | |
7 | Repair the open HO2S 2 ignition 1 voltage circuit to HO2S 2. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
8 | Repair the open HO2S 2 heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
9 | Inspect the HO2S 2 harness terminals for a poor connection. Refer to Wiring Repairs in Wiring Systems. 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 |
Inspect the HO2S 2 high signal or HO2S 2 low signal circuit for a poor connection at the HO2S 2 harness connector. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 | |
12 | Inspect the HO2S 2 low signal circuit for a poor connection at the PCM. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 |
13 | Inspect the HO2S 2 high signal circuit for a poor connection at the PCM. If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 |
14 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
15 | Repair the short to ground in the HO2S 1 or HO2S 2 ignition 1 voltage circuit and replace the fuse. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
16 |
Important:: If the engine has just been operating, allow the engine to cool for one-half hour before proceeding.
Does the DTC run and pass? | 600 mV 300 mV | 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 | |
