Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias, voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements within each HO2S heat the sensor. The powertrain control module (PCM) controls the HO2S heater control circuit. The HO2S heater diagnostic monitors the current draw through the HO2S output driver module (ODM) when the engine is running. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
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 signal circuit |
| • | A HO2S 1 heater ignition voltage circuit |
| • | A HO2S 1 heater low control circuit |
DTC Descriptor
This diagnostic procedure support the following DTC:
DTC P0135 HO2S Heater Performance Bank 1 Sensor 1
Conditions for Running the DTC
The Following conditions must be met:
| • | DTCs P0030, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0464 are not set. |
| • | DTCs P2A01, P0401 (where applicable), P0420 are not commanding fuel. |
| • | The system voltage is between 9-18 volts. |
| • | The scan tool special functions are not active. |
| • | The following conditions must also be met: |
| - | The Engine Run Time parameter is more than 100 seconds. |
| - | The ECT Sensor parameter is more than 65°C (149°F). |
| - | The MAF sensor parameter is between 4 g/s and 30 g/s. |
| - | The Engine Speed parameter is between 600-3,000 RPM. |
| - | The above conditions have been met for more than 2 seconds. |
Conditions for Setting the DTC
| • | The HO2S heater current is less than 0.31 amps or more than 1.43 amps for at least 17 out of 25 test samples. |
| • | Five tests during each trip with a 30 second delay between each test. |
| • | Each test is one second. |
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 - Vehicle? | -- | Go to Step 2 | |||||
2 |
Is the amperage within the specified range? | 0.30-1.45 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 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 . 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 . 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 . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 11 | ||||
11 | Measure the resistance from the ignition 1 voltage circuit of 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 . 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 . 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 1 heater low control circuit. Refer to Wiring Repairs . Did you complete the repair. | -- | Go to Step 18 | -- | ||||
15 | Repair the open or high resistance in the HO2S 1 ignition 1 voltage circuit. Refer to Wiring Repairs . 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 Control Module References for replacement, setup, and programming. 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 | |||||
