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 in Closed Loop. 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.
The HO2S 1 has the following circuits:
| • | A HO2S 1 high signal circuit |
| • | A HO2S 1 low reference circuit |
| • | A HO2S 1 heater ignition voltage circuit |
| • | A HO2S 1 heater low control circuit |
| • | A low reference loop circuit |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0206, P0401, P0442, P0443, P0446, P0449, P0455, P0496 are not set. |
| • | The Engine Run Time parameter is more than 3 minutes. |
| • | The ECT Sensor parameter is more than 65°C (158°F). |
| • | The Engine Speed parameter is between 650-2,500 RPM. |
| • | The MAF Sensor parameter is between 4-30 g/s. |
| • | The system voltage is between 9-18 volts. |
Conditions for Setting the DTC
The PCM detects that the 02 Heater Current parameter is less than 0.25 A or more than 0.90 A for longer than 3 minutes and 10 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: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
2 |
Is the amperage within the specified range? | 0.25-0.90 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 |
Important: Use a known good ground. DO NOT use the heated oxygen sensor (HO2S) 1 heater low control circuit or the HO2S 1 low reference circuit.
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 5 | ||||
5 | Test the HO2S 1 heater ignition 1 voltage fuse for an open. Refer to Circuit Testing in Wiring Systems. Is the fuse open? | -- | Go to Step 10 | Go to Step 15 | ||||
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 8 | ||||
7 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 12 | ||||
8 |
Is the resistance within the specified range? | 0-5 ohms | Go to Step 13 | Go to Step 14 | ||||
9 | Test the HO2S 1 heater low control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 13 | ||||
10 | Test the HO2S 1 heater ignition voltage circuit for a short to ground and replace the fuse. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 11 | ||||
11 | Measure the resistance from the HO2S ignition 1 voltage circuit, on the sensor side of the HO2S harness connector, to each of the following circuits:
Is the resistance less than the specified value? | 5 ohms | Go to Step 16 | Go to Intermittent Conditions | ||||
12 | Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. 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 18 | Go to Step 16 | ||||
13 | Test for an intermittent and for a poor connection at the harness connector of the 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 18 | Go to Step 17 | ||||
14 | Repair the open or high resistance in the HO2S heater low control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- | ||||
15 | Repair the open or high resistance in the HO2S ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- | ||||
16 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||
17 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||
18 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 19 | ||||
19 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
