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 startup) and only once during an ignition cycle. When the engine is started the PCM will monitor the HO2S voltage. When the Bank 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, the DTC 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 startup (more total airflow or higher startup engine coolant temperature = shorter time to HO2S activity).
Conditions for Running the DTC
| • | No active fuel trim, fuel injector circuit, Misfire, EVAP, EGR, AIR, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs present. |
| • | P0131 or P0132 not set |
| • | System voltage is between 9 and 18 volts. |
| • | Intake Air Temperature (IAT) is less than 45°C (113°F) at startup. |
| • | Engine Coolant Temperature (ECT) is less than 40°C (104°F) at startup. |
| • | IAT and ECT are within 15°C (27°F) of each other at start-up. |
| • | Average mass airflow for the sample period is less than 26 g/s. |
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 ranges between 50 and 130 seconds depending on engine coolant temperature at startup and average air flow since startup.
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 three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A last test failed (current DTC) clears when the diagnostic runs and does not fail. |
| • | A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | Use a scan tool in order to clear the MIL/DTC. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) 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 determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
If the problem is intermittent, refer to Intermittent Conditions .
The heated oxygen sensors (HO2S) require an air reference for proper operation. The air reference is supplied through the HO2S wiring. Inspect the HO2S wires and connections for breaks or contamination. Do not use solder to repair HO2S wiring. Solder will obstruct the air path. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems for proper repair procedures.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition On and the engine Off the exhaust usually contains a high oxygen content. With the engine Off the HO2S voltage will usually decrease from the initial (bias) voltage due to the high oxygen content.
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This step checks for a proper HO2S heater ignition feed and ground supply.
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This step checks for proper PCM and signal circuit operation.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||
|
Important: The HO2S must be cool before proceeding with diagnosis. The Ignition must remain Off for at least one half hour before proceeding with diagnosis.
The ignition is On and the engine is Off. The ignition is On and the engine is Off. Does the HO2S voltage increase or decrease from the initial voltage by at least the value specified? | 150 mV | |||||||||||
3 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Repair any of the above conditions as necessary. Was a condition found and repaired? | -- | Refer to Diagnostic Aids. | |||||||||
Turn the ignition On while leaving the engine Off. Is the test lamp illuminated? | -- | |||||||||||
Ensure the ignition is On while the engine is Off. Is the HO2S voltage less than the value specified? | 20 mV | |||||||||||
6 | Connect the test lamp J 35616-200 between the HO2S heater ignition feed circuit terminal (engine harness side) and a known good ground. Ensure the ignition is On while the engine is Off. Is the test lamp illuminated? | -- | ||||||||||
7 |
Is the individual resistance of both circuits less than the value specified? | 5 ohms | ||||||||||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||
9 | Repair the open HO2S heater ground circuit. Is the action complete? | -- | -- | |||||||||
10 | Repair the lack of power on the HO2S heater ignition feed circuit. If the fuse is blown repair the short to ground on the circuit. A blown fuse or lack of power to the fuse may cause other DTCs or symptoms to be present. Is the action complete? | -- | -- | |||||||||
11 | Repair the circuit that measured high resistance. Is the action complete? | -- | -- | |||||||||
12 |
Was a PCM terminal repair made? | -- | ||||||||||
13 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||||
14 |
Important: The HO2S must be cool before proceeding with diagnosis. The Ignition must remain Off for at least one half hour before proceeding with diagnosis.
The ignition is On and the engine is Off. The ignition is On and the engine is Off. Does the HO2S voltage increase or decrease from the initial voltage by at least the value specified? | 150 mV | ||||||||||
15 | Review Captured Info using the scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
