Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0- 1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and then provide an accurate voltage signal. The PCM controls the HO2S 1 heater low control circuit with a low side driver. The HO2S 1 heater diagnostic monitors the current draw through the HO2S low side driver when the engine is running. If the PCM detects there is a circuit fault present on the HO2S 1 heater low control circuit, the following DTCs will set.
| • | P0030 for bank 1 sensor 1 |
| • | P0036 for bank 1 sensor 2 |
| • | P0050 for bank 2 sensor 1 |
| • | P0056 for bank 2 sensor 2 |
Each HO2S has the following circuits:
| • | The HO2S high signal circuit |
| • | The HO2S low signal circuit |
| • | The HO2S heater ignition 1 voltage circuit |
| • | The HO2S heater low control circuit |
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The PCM detects the affected HO2S heater low control circuit is open or shorted for longer than 2 seconds.
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. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the parameter display Fault? | -- | Go to Step 5 | Go to Step 3 |
3 |
Does the parameter display Fault? | -- | Go to Step 5 | Go to Step 4 |
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions |
5 | Inspect the fuse that powers the affected heated oxygen sensor (HO2S) for an open. Is the fuse open? | -- | Go to Step 6 | Go to Step 7 |
6 | Test the affected HO2S ignition 1 voltage circuit for a short to ground. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 14 |
7 |
Important: Use a known good ground. DO NOT use the HO2S heater low control circuit or the HO2S low signal circuit. Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 17 |
8 | Connect a test lamp between the HO2S ignition 1 voltage circuit and the HO2S heater low control circuit, on the engine harness side. Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 9 |
9 | Start the engine. Does the test lamp illuminate? | -- | Go to Step 15 | Go to Step 10 |
10 |
Is the voltage more than the specified value? | 1 V | Go to Step 12 | Go to Step 13 |
11 | Test the HO2S heater low control circuit for a short to ground. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 16 |
12 | Test the HO2S heater low control circuit for a short to voltage. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 16 |
13 | Test the HO2S heater low control circuit for an open. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 16 |
14 |
Important: Perform the following test on any HO2S that is supplied voltage by the suspect circuit. Test the HO2S ignition 1 voltage circuit, on the sensor side of the HO2S connector, for a short to ground. Refer to Circuit Testing in Wiring Systems. Is the sensor shorted to ground? | -- | Go to Step 18 | Go to Intermittent Conditions |
15 | Test for shorted terminals and poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 18 |
16 | Test for shorted terminals and poor connections at the powertrain control module (PCM). 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 20 | Go to Step 19 |
17 | Repair the open or high resistance in the HO2S ignition 1 voltage circuit. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | -- |
18 |
Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section. Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | -- | Go to Step 20 | -- |
19 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- |
20 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 21 |
21 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
