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. This diagnostic will only run once per ignition cycle. The PCM monitors the rich-to-lean and lean-to-rich transition time. A transition is defined as, the HO2S voltage changes from greater than 625 mV to less than 250 mV or from less than 250 mV to greater than 625 mV. If the PCM detects that the difference between the rich-to-lean average transition time and lean-to-rich average transition time is greater than a specified value, DTC P1134 sets for HO2S bank 1 sensor 1, or DTC P1154 sets for HO2S bank 2 sensor 1.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P1134 HO2S Transition Time Ratio Bank 1 Sensor 1 |
| • | DTC P1154 HO2S Transition Time Ratio Bank 2 Sensor 1 |
Conditions for Running the DTC
| • | DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0128, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0169, P0178, P0179, P0200, P0220, P0442, P0446, P0452, P0453, P0455, P0496, P1125, P1258, P1516, P2101, P2108, P2135, U0107 are not set. |
| • | The ECT Sensor parameter is more than 60°C (140°F). |
| • | The EVAP Purge Solenoid Command parameter is more than 1 percent. |
| • | The MAF Sensor parameter is between 20-55 g/s. |
| • | The Engine Speed parameter is between 1,200-3,000 RPM. |
| • | The TP Indicated Angle parameter is 5 percent more than the value observed at idle. |
| • | The Loop Status parameter is closed. |
| • | The Ignition 1 Signal parameter is between 10-18 volts. |
| • | The Fuel Alcohol content parameter is less than 90 percent. |
| • | The Fuel Tank Level Remaining parameter is more than 10 percent. |
| • | The Engine Run Time parameter is more than 160 seconds. |
| • | The above conditions are met for 1 second. |
| • | This diagnostic runs one time per drive cycle once the above conditions are met. |
Conditions for Setting the DTC
The PCM detects that the difference between the HO2S rich-to-lean average transition time and the lean-to-rich average transition time is more than a calibrated value for 100 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 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: 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 | |||||||||
Is the HO2S voltage parameter varying above and below the specified range? | 250-625 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 | Test the HO2S high signal circuit for an open or high resistance. Refer to the following procedures: Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||
6 |
Is the HO2S voltage parameter less than the specified value? | 100 mV | Go to Step 8 | Go to Step 7 | ||||||||
7 | Test the HO2S low signal circuit for an open or high resistance. Refer to the following procedures: Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||
8 | Test for shorted terminals and for poor connections at the HO2S. Refer to the following procedures: Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||||
9 | Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to the following procedures: Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||
10 |
Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section. Important: The HO2S may be damaged due to contamination. Prior to replacing the HO2S inspect for the following sources of contamination:
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 12 | -- | ||||||||
11 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||
12 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 | ||||||||
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||
