Circuit Description
The PCM supplies a bias voltage (approximately 450 mV) on the Heated Oxygen Sensor (HO2S) signal high and low circuits. When you turn the ignition to the ON position, battery voltage is supplied to the HO2S heater. As the heater reaches the operating temperature, the HO2S voltage responds by changing from a bias voltage range to the normal operation. Typically, as the HO2S reaches the operating temperature, the HO2S voltage goes from a bias voltage to a voltage below 300 mV. Depending on the exhaust gas content, it is possible for the HO2S voltage to go above 450 mV.
The PCM runs the heater test only on a cold start (depends on the cumulative air flow) and only once an ignition cycle. When you start the engine the PCM monitors the HO2S voltage. When the HO2S voltage goes above or below the bias range threshold, the PCM determines how much time it took. If the PCM detects that the process took too much time for the HO2S to enter into normal operating range, a DTC will set. The time the process takes the HO2S to reach operating temperature is based on the amount of air that flows into the engine.
Conditions for Setting the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0220, P0221, P0225, P0226, P0335, P0336, P0351, P0352, P0353, P0354, P0355, P0356, P0357, P0358, P1111, P1112, P1120, P1121 P1125, P1220, P1221, P1258, P1514, P1515, P1516, P1517 not set |
| • | The engine is started and the intake air and the engine coolant temperatures are less than 50°C (122°F) and are within 8°C (14.5°F) of each other at start-up. |
| • | The system voltage is between 10 volts and 16 volts. |
| • | The engine air flow is less than 30 g/s. |
| • | The AIR and the Catalyst diagnostics are not active. |
| • | The HO2S voltage remains between 300 mV and 700 mV for a predetermined amount of time (depends on engine coolant temperature and air flow). |
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 OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
| • | Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For an intermittent condition, refer to Symptoms . |
| • | The heater diagnostic will only run on a cold start and run once per ignition cycle. |
| • | An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provides the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Body and Accessories/Wiring Systems. |
| • | For an intermittent condition, refer to Symptoms . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The engine must be allowed to cool, as the HO2S may be at operating temperature and no drop or rise in HO2S voltage would occur. If the HO2S voltage stays between 300-700 mV indicates the HO2S heater is inoperative. For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit prevents damage to the harness connector terminals.
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If more than one HO2S heater DTC is set, this is a good indication that the HO2S fuse is open. Check all the related circuits going to all of the heated oxygen sensors for a short to ground. If all wiring checks to be OK, it may be necessary to disconnect each HO2S one at a time to locate a shorted sensor.
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Lower the exhaust system to gain sufficient access to the HO2S and/or the HO2S connector if necessary. Refer to Engine/Engine Exhaust. This step checks whether the B+ supply is available at the sensor.
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This step checks whether a ground is available at the sensor.
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This step checks whether the HO2S heater element is internally open.
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Inspect the ignition feed circuits at the Underhood Electrical Center for poor connections.
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Check the splice pack for the ground circuits for an open if more then one heater DTC sets.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check ? | -- | ||
|
Important: If you have been operating the engine, allow the engine to cool for about one half hour before proceeding.
Does the HO2S voltage go from a bias voltage to above or below the specified values? | 300-700 mV | Go to Diagnostic Aids | ||
Inspect the fuse for the HO2S ignition feed. Is the HO2S fuse open? | -- | |||
Is the test lamp illuminated? | -- | |||
Connect a test lamp J 35616-200 between the HO2S ignition feed and the HO2S heater ground. Is the test lamp illuminated? | -- | |||
Measure the resistance between the HO2S ignition feed and the HO2S heater ground at the HO2S pigtail using the DMM J 39200 . Is the HO2S resistance within the specified values? | 3.5-14.0ohms | |||
Repair the open in the HO2S ignition feed circuit to the HO2S. Refer to Body and Accessories/Wiring Systems. Is the action complete? | -- | -- | ||
Repair the open in the HO2S heater ground circuit. Refer to Body and Accessories/Wiring Systems. Is the action complete? | -- | -- | ||
9 |
Did you find a poor connection? | -- | ||
10 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |
11 |
Is the action complete? | -- | -- | |
12 |
Does the scan tool indicate that this test ran and passed? | -- | ||
13 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
