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 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 at an increased distance from the engine.
The powertrain control module (PCM) will run the heater test only after a cold start, which is determined by the engine coolant temperature (ECT) and the intake air temperature (IAT) at the time of startup. The heater test will also run only once during an ignition cycle. When the engine is started, the PCM will monitor the HO2S voltage. When the HO2S voltage indicates that the sensor is sufficiently active, 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, the DTC will set. The appropriate length of time for the HO2S to reach operating temperature is calculated based on the engine coolant temperature at start-up and the average mass airflow (MAF) since startup. The more total airflow and the higher the startup engine coolant temperature (ECT), the less time should be required for HO2S activity.
Conditions for Running the DTC
| • | DTCs P0137 or P0138 are not set. |
| • | The system voltage is between 9-18 volts. |
| • | The intake air temperature (IAT) is less than 45°C (113°F) at startup. |
| • | The engine coolant temperature (ECT) is less than 40°C (104°F) at startup. |
| • | The IAT and ECT are within 10°C (50°F) of each other at startup. |
| • | The average MAF for the sample period is less than 25 g/s. |
Conditions for Setting the DTC
The HO2S 2 voltage remains within 150 mV of the bias voltage, approximately 450 mV, for more than a predetermined time. The amount of time ranges between 50-130 seconds depending on the engine coolant temperature at startup and 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. |
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 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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As the heater warms the oxygen sensor to operating temperature, the HO2S will generate an output voltage proportional 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, or bias, voltage due to the high oxygen content.
-
This step checks for a correct HO2S heater ignition feed and ground supply.
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This step checks for proper PCM and signal circuit operation.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 | Did DTC P0036 also set? | -- | Go to DTC P0036 | Go to Step 3 | ||||||||
|
Important: If the engine has just been operating, allow the engine to cool until near bias voltage is observed on the scan tool before proceeding.
Does the HO2S 2 voltage go to above or below the previously stabilized voltage, by at least as much as the specified value within 2 minutes? | 150 mV | Go to Step 4 | Go to Step 5 | |||||||||
4 | 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. Refer to Wiring Repairs in Wiring Systems. Was a condition found and repaired? | -- | Go to Step 15 | Go to Diagnostic Aids | ||||||||
Is the test lamp illuminated? | -- | Go to Step 6 | Go to Step 7 | |||||||||
Is the HO2S voltage less than the value specified? | 20 mV | Go to Step 9 | Go to Step 8 | |||||||||
7 | Connect a test lamp between the HO2S ignition 1 voltage circuit terminal on the engine harness side, and a known good ground. Ensure the ignition is ON while the engine is OFF. Is the test lamp illuminated? | -- | Go to Step 10 | Go to Step 11 | ||||||||
8 |
Is the individual resistance of both circuits less than the value specified? | 5 ohms | Go to Step 13 | Go to Step 12 | ||||||||
9 | Replace the HO2S. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||
10 | Repair the open HO2S heater low control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||||
11 | Repair the lack of power on the HO2S ignition 1 voltage feed circuit. Refer to Wiring Repairs in Wiring Systems. If the fuse is open, repair the short to ground on the circuit. An open fuse or lack of power to the fuse may cause other DTCs or symptoms to be present. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||||
12 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||||
13 |
Was a PCM terminal repair made? | -- | Go to Step 15 | Go to Step 14 | ||||||||
14 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||
15 |
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.
Does the HO2S voltage increase or decrease from the initial voltage by at least the value specified? | 150 mV | Go to Step 16 | Go to Step 2 | ||||||||
16 |
Does the DTC run and pass? | -- | Go to Step 17 | Go to Step 2 | ||||||||
17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display and DTCs that you have not diagnosed? | -- | System OK | |||||||||
