Refer to Engine Controls Schematics
Heated O2 Sensors
.
Circuit Description
Heated oxygen sensors (HO2S) are used to minimize the amount of time required to enter closed loop fuel control operation and to allow accurate catalyst monitoring. The HO2S 2 heater is fed power directly from ignition 1. The HO2S 2 heater control circuit (heater ground) is connected to the PCM. The PCM controls HO2S heater operation by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the PCM. When the PCM is commanding a component on, the voltage on the control circuit should be near 0 volts. When the PCM is commanding a component off, the voltage potential on the component control circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, a DTC will set.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The PCM detects an open or a short on the heater control circuit.
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 turns the MIL OFF after 3 consecutive drive trips during which the diagnostic runs and passes. |
| • | A last test failed, or the current DTC, clears when the diagnostic runs and passes. |
| • | A History DTC clears after 40 consecutive warm-up cycles, if no other emission related diagnostic failures are reported. |
| • | Use a scan tool in order to clear the MIL diagnostic trouble code. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module Description , Clearing Diagnostic Trouble Codes. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help to determine how often the condition occurs that caused the DTC to set . This may assist in diagnosing the condition.
If the problem is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
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The scan tool displays OK when the circuit is operating properly. Fault is displayed if the circuit is open or shorted.
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Ensures 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 malfunctioning.
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Checks the HO2S heater ground circuit. The engine must be running for the PCM to enable the heater.
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Checks for an open or high resistance HO2S heater control circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |
Does the scan tool indicate OK? | -- | Go to Diagnostic Aids. | Go to Step 3 | |
3 | Inspect the fuse for the HO2S 2 ignition feed circuit. Is the fuse open? | -- | Go to Step 11 | Go to Step 4 |
Important:: Use a known good ground. Do not use the HO2S 2 heater ground circuit or the HO2S 2 low circuit. Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 6 | |
Is the resistance within the specified range? | 0-5 ohms | Go to Step 12 | Go to Step 8 | |
7 | Repair open HO2S 2 ignition feed circuit to HO2S 2. Refer to Heated Oxygen Sensor Wiring Repairs . Is the action complete? | -- | Go to Step 14 | -- |
8 | Repair the open or the high resistance HO2S 2 heater control circuit. Refer to Heated Oxygen Sensor Wiring Repairs . Is the action complete? | -- | Go to Step 14 | -- |
9 |
Was a problem found and corrected? | -- | Go to Step 14 | Go to Step 10 |
10 | Replace HO2S 2. Refer to Heated Oxygen Sensor Replacement in Wiring Systems. Is the action complete? | -- | Go to Step 14 | -- |
11 | Locate and repair the short to ground in HO2S 2 ignition feed circuit and replace the fuse. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Is action complete? | -- | Go to Step 14 | -- |
12 |
Was a problem found and corrected? | -- | Go to Step 14 | |
13 |
Important:: The PCM must be reprogrammed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming Is the action complete? | -- | Go to Step 14 | -- |
14 |
Does the scan tool indicate OK? | -- | Go to Step 15 | Go to Step 2 |
15 |
Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
