Circuit Description
The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to the operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches the operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean out" the mixture, when the HO2S detects a rich exhaust condition.
This DTC determines if the HO2S heater circuit is functioning properly by monitoring the time required for the HO2S to reach the operating temperature. This DTC sets when the powertrain control module (PCM) fails to detect HO2S voltage transitions above and below the bias range within a specified time.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404, or P1441 are not set. |
| • | The HO2S voltage is between 425-475 mV at engine start-up. |
| • | The intake air temperature (IAT) and the engine coolant temperature (ECT) are less than 50°C (122°F), and are within 8°C (14.5°F) of each other at engine start-up. |
| • | The ignition 1 signal is between 9-18 volts. |
| • | Intrusive tests are not in progress. |
| • | Scan tool output controls are not active. |
| • | The scan tool is disconnected. |
Conditions for Setting the DTC
The HO2S voltage remains within 150 mV of the start-up voltage for a predetermined amount of time, based on ECT and air flow.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature, and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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After the ignition is turned ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.
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All sensors must be disconnected to isolate a short to ground in the HO2S ignition 1 voltage circuit.
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Resistance within the specified range indicates the HO2S heater is OK.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
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Important: If DTC P0300 is also set, diagnose P0300 first. Refer to DTC P0300 . Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.
Does the HO2S voltage go from bias voltage to more than or less than the specified range? | 350-550 mV | Go to Step 3 | Go to Step 4 | |
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
4 | Is the ENG 1 fuse open? | -- | Go to Step 7 | Go to Step 5 |
5 |
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 11 |
6 |
Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 12 |
Did you find and correct a short to ground in the ignition 1 voltage circuit? | -- | Go to Step 14 | Go to Step 8 | |
8 |
Important: Perform the following test on HO2S bank 1 sensor 1, HO2S bank 2 sensor 1, and HO2S bank 1 sensor 2. A condition in any sensor will cause this DTC to set. Test the HO2S ignition 1 voltage circuit, sensor side, for a short to the HO2S body. Refer to Circuit Testing in Wiring Systems. Did you find the condition? | -- | Go to Step 13 | Go to Step 9 |
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Important: Perform the following test on HO2S bank 1 sensor 1, HO2S bank 2 sensor 1, and HO2S bank 1 sensor 2. A condition in any sensor will cause this DTC to set. Measure the resistance between the HO2S ignition 1 voltage circuit, sensor side, and the HO2S heater ground circuit, sensor side. Refer to Circuit Testing in Wiring Systems. Does the resistance of any sensor measure above or below the specified range? | 2-50 ohms | Go to Step 13 | Go to Intermittent Conditions | |
10 | Inspect for poor connections at the harness connector of the affected HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
11 | Repair the open in the ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- |
12 | Repair the open in the HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 14 | -- | |
13 | Replace the affected HO2S refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 |
15 | With a scan tool observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
