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 to 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 1 low side driver when the engine is running. If the PCM detects that the HO2S 1 heater low control circuit current level is not within the calibrated range, DTC P0135 will set for bank 1 sensor 1, or DTC P0155 will set for bank 2 sensor 1. This diagnostic may run up to 5 tests per ignition cycle, with a minimum of 30 seconds between tests.
Each HO2S 1 has the following circuits:
| • | The HO2S 1 high signal circuit |
| • | The HO2S 1 low reference circuit |
| • | The HO2S 1 ignition 1 voltage circuit |
| • | The HO2S 1 heater low control circuit |
Conditions for Running the DTC
| • | DTCs P0030, P0036, P0050, P0056, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0201-P0206, P0442, P0443, P0446, P0449 are not set. |
| • | The Engine Run Time parameter is more than 2 minutes. |
| • | The ECT Sensor parameter is more than 65°C (149°F). |
| • | The HO2S heater is not being commanded by a scan tool. |
| • | The Engine Speed parameter is between 600-3,000 RPM. |
| • | The MAF Sensor parameter is between 4-30 g/s. |
| • | The system voltage is between 9-18 volts. |
| • | The above conditions have been met for 2 seconds. |
Conditions for Setting the DTC
The PCM detects that the HO2S 1 Heater parameter is less than 0.31 A or more than 1.43 A for longer than 20 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if high resistance is present in the HO2S 1 ignition 1 voltage circuit.
-
This step determines if high resistance is present in the HO2S 1 heater low control circuit.
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 |
Important: The HO2S Heater parameter may toggle to 0.00 A momentarily.
Is the amperage within the specified range? | 0.31-1.43 A | Go to Step 3 | Go to Step 4 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
4 | Test the fuse that powers the affected heated oxygen sensor (HO2S) 1 for an open. Refer to Circuit Testing in Wiring Systems. Is the fuse open? | -- | Go to Step 8 | Go to Step 5 |
Important: Use a known good ground. DO NOT use the heated oxygen sensor (HO2S) 1 heater low control circuit or the HO2S 1 low signal circuit. Is the voltage more than the specified amount below vehicle system voltage? | 0.5 V | Go to Step 12 | Go to Step 6 | |
Is the voltage more than the specified value? | 0.5 V | Go to Step 7 | Go to Step 10 | |
7 | Test the HO2S 1 heater low control circuit for an open or high resistance. 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 15 | Go to Step 11 |
8 | Test the HO2S 1 ignition 1 voltage circuit for a short to ground and replace the fuse. 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 15 | Go to Step 9 |
9 |
Important: Perform the following test on any HO2S that is supplied voltage by the suspect circuit. Test the HO2S 1 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 any sensor shorted to ground? | -- | Go to Step 13 | Go to Intermittent Conditions |
10 | Test for an intermittent and for a poor connection at the HO2S 1. 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 15 | Go to Step 13 |
11 | Test for intermittent 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 15 | Go to Step 14 |
12 | Repair the open or high resistance condition in the HO2S 1 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 15 | -- |
13 |
Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section. Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 15 | -- |
14 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- |
15 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 16 |
16 | 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 |
