Circuit Description
Heated oxygen sensors (HO2S) are used to minimize the amount of time required for Closed Loop fuel control operation, and to allow accurate catalyst monitoring. The oxygen sensor (O2S) heater greatly decreases the amount of time required for fuel control sensor HO2S 1 to become active. The O2S 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 powertrain control module (PCM) will run the heater test only after a cold start, and only once during an ignition cycle. A cold start is determined by the engine coolant (ECT) and intake air temperature (IAT) at the time of startup. When the engine is started, the PCM will monitor the HO2S voltage. When the HO2S voltage indicates a sufficiently active sensor, the PCM measures how much time has elapsed since startup. If the PCM determines that too much time was required for the HO2S 1 to become active, this DTC will set. The time required for the HO2S to reach operating temperature is based on the ECT at start-up and the average mass air flow (MAF) since startup. A higher average airflow or higher startup ECT equals a shorter time to HO2S activity.
Conditions for Running the DTC
| • | None of the following active DTCs are present: |
| - | Throttle position (TP) sensor |
| - | Evaporative emissions (EVAP) system |
| - | Misfire |
| - | Intake air temperature (IAT) sensor |
| - | Manifold absolute pressure (MAP) sensor |
| - | Fuel trim |
| - | Fuel injector circuit |
| - | EGR pintle position |
| - | Engine coolant temperature (ECT) sensor |
| - | Crankshaft position (CKP) sensor |
| - | Mass air flow (MAF) sensor |
| • | The system voltage is between 9 and 16 volts. |
| • | The intake air temperature (IAT) is less than 35°C (95°F) at startup. |
| • | The engine coolant temperature (ECT) is less than 35°C (95°F) at startup. |
| • | The IAT and ECT are within 6°C (11°F) of each other at start-up. |
| • | The average mass airflow for the sample period is less than 20 g/s (VIN K). |
| OR |
| The average mass airflow for the sample period is less than 19 g/s (VIN 1). |
Conditions for Setting the DTC
The HO2S 1 voltage remains within 150 mV of the bias voltage (approximately 450 mV) for more time than necessary. The amount of time ranges between 50 and 80 seconds depending upon the engine coolant temperature at startup and the average mass air flow since startup.
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
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:
| • | Poor connections at the PCM or the HO2S |
| Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the malfunction. |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
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.
-
This step ensures that the ignition feed circuit to the HO2S is not open or shorted. The test lamp should be connected to a good ground in case the HO2S low or HO2S heater ground circuit is faulty.
-
This step tests the HO2S heater ground circuit.
-
This step 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.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||
|
Important: If engine has been operating, allow the engine to cool for about one half hour or until the bias voltage is observed on the scan tool before proceeding.
Does the HO2S voltage change from bias voltage to more than the first specified value or less than the second specified value? | 600 mV 300 mV | Go to Diagnostic Aids | ||
3 | Inspect the HO2S ignition feed fuse. Is the fuse open? | -- | ||
|
Important: Use a known good ground. Do not use the HO2S heater ground or low circuit.
Does the test lamp illuminate? | -- | |||
Connect the test lamp between the HO2S ignition feed circuit and the HO2S heater ground. Does test lamp illuminate? | -- | |||
Is the resistance within the specified range? | 5-10 ohms | |||
7 | Repair the open HO2S ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
8 | Repair the open HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
9 |
Did you find and correct the condition? | -- | ||
10 | Test the HO2S signal and low circuits for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
11 | Inspect the HO2S signal or low circuits for a faulty connection at the PCM and the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring System. Did you find and correct the condition? | -- | ||
12 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the repair? | -- | -- | |
13 | Repair the short to ground in the HO2S ignition feed circuit and replace a faulty fuse. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
14 |
Important: If engine has been operating, allow the engine to cool for about one half hour before proceeding.
Does the HO2S voltage change from bias voltage to more than the first specified value or less than the second specified value? | 600 mV 300 mV | System OK |
