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 in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTC P0131 sets for HO2S bank 1 sensor 1, or DTC P0151 sets for HO2S bank 2 sensor 1.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 |
| • | DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 |
Conditions for Running the DTC
| • | DTCs P0068, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0128, P0200, P0220, P1125, P1516, P2101, P2108, P2135, U0107 are not set. |
| • | The Loop Status parameter is closed. |
| • | The Ignition 1 Signal parameter is between 10-18 volts. |
| • | The Fuel Tank Level Remaining parameter is more than 10 percent. |
| • | The TP Indicated Angle parameter is between 3-70 percent more than the value observed at idle. |
| • | The above conditions are met for 2 seconds. |
| • | This diagnostic runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The PCM detects that the affected HO2S voltage parameter is less than 200 mV for 165 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. |
| • | The control module commands the Loop Status open. |
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 number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Component Connector End Views | ||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||||||
Is the HO2S voltage parameter varying above and below the specified range? | 300-600 mV | Go to Step 3 | Go to Step 4 | |||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections | ||||||||||||||
4 |
Is the HO2S voltage parameter less than the specified value? | 100 mV | Go to Step 6 | Go to Step 5 | ||||||||||||||
5 |
Is the HO2S voltage parameter less than the specified value? | 100 mV | Go to Step 7 | Go to Step 8 | ||||||||||||||
6 | Test the HO2S high signal circuit for a short to ground. Refer to the following: Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 9 | ||||||||||||||
7 | Test the HO2S low signal circuit for a short to the HO2S heater low control circuit. Refer to the following: Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 10 | ||||||||||||||
8 | Test the HO2S high signal circuit for an open or high resistance. Refer to the following: Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||||||||||||
9 | Test the HO2S high signal circuit for a short to the following circuits:
Refer to the following: Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||||||||||||
10 |
Caution: Refer to Silicon Contamination of Heated Oxygen Sensors Caution in the Preface section.
Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 11 | ||||||||||||||
11 | Test for shorted terminals and for poor connections at the HO2S. Refer to the following: Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 | ||||||||||||||
12 | Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to the following: Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||||||||||||
13 | Replace the affected HO2S. 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 Control Module References for replacement, setup, and programming. 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? | -- | System OK | |||||||||||||||
