Refer to
Cell 20: Engine Data Sensors-HO2S 1, Ho2S 2
.
Circuit Description
Heated oxygen sensors are used to minimize the amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of 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 and intake air temperature at the time of start up) and 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 looks at how much time has elapsed since startup. If the PCM determines that too much time was required for the HO2S 2 to become active, a DTC P0141 will set. The time it should take the HO2S to reach operating temperature is based on the engine coolant temperature at start-up and the average Mass Air Flow since start-up (higher average airflow or higher start-up engine coolant temperature = shorter time to HO2S activity).
Conditions for Running the DTC
| • | No active TP, MAP, MAF, ECT, IAT, or CKP Sensor, misfire, fuel injector circuit, EVAP, Fuel trim, EGR, DTCs present. |
| • | Intake Air Temperature (IAT) is less than 35°C (95°F) at start up. |
| • | Engine Coolant Temperature (ECT) is less than 35°C (95°F) at start-up. |
| • | IAT and ECT are within 6°C (43°F) of each other at start-up. |
| • | Average mass airflow for the sample period is less than 28 gm/s. |
| • | System voltage between 9.0 V and 16.0 V. |
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 than it should. The amount of time varies depending on engine coolant temperature at start-up and average air flow since start-up, but will not exceed 4.5 minutes.
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 conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Check for the following conditions:
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Poor terminal connection. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table:
-
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.
-
Checks that the ignition feed 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 faulty.
-
Checks the HO2S heater ground circuit.
-
Checks for an open or shorted HO2S heater element. The heater element resistance will vary according to HO2S temperature (a hot HO2S heater element will measure a much higher resistance than a HO2S heater element at room temperature). It is important to allow the HO2S to cool before measuring HO2S heater element resistance.
-
An open HO2S signal or low circuit can cause the HO2S heater to appear faulty. Check these circuits before replacing the sensor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain on-Board Diagnostic system Check performed? | -- | ||
|
Important: :
Does HO2S voltage go from bias voltage to greater than the first specified value or less than the second specified value? | 600 mV 300 mV | Go to Diagnostic Aids | ||
3 | Inspect fuse for HO2S 2 ignition feed. Is the fuse open? | -- | ||
Does test lamp illuminate? | -- | |||
Connect test lamp between HO2S 2 ignition feed and HO2S 2 heater ground. Does J 35616-200 test lamp illuminate? | -- | |||
Is HO2S resistance within the specified values? | 5-6 ohms | |||
7 | Repair open HO2S 2 ignition feed circuit to HO2S 2. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
8 | Repair open HO2S 2 heater ground circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
9 |
Was a poor connection found? | -- | ||
10 |
Was a problem found? | -- | ||
Check for a poor HO2S 2 signal or low circuit terminal connection at the HO2S 2 harness connector and replace terminal(s) if necessary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Did any terminals require replacement? | -- | |||
12 | Check for poor HO2S 2 low circuit terminal connection at the PCM and replace terminal if necessary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Did the terminal require replacement? | -- | ||
13 | Check for poor HO2S 2 signal circuit terminal connection at the PCM and replace terminal if necessary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Did the terminal require replacement? | -- | ||
14 | Replace HO2S 2. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |
15 | Locate and repair short to ground in HO2S 2 ignition feed circuit and replace faulty fuse. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
16 |
Important: : If engine has just been operating, allow engine to cool for about one half hour before proceeding.
Does HO2S voltage go from bias voltage to greater than the first specified value or less than the second specified value? | 600 mV 300 mV | System OK |
