Circuit Description
Oxygen sensors (O2S) are used for fuel control and post catalyst monitoring. Each O2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The O2S must reach operating temperature to provide an accurate voltage signal. A heating element in O2S 2 minimizes the time required for the sensor to reach operating temperature. The powertrain control module (PCM) supplies the O2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the O2S voltage signal. Once the O2S reaches operating temperature and Closed Loop is achieved, the O2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High O2S voltage indicates a rich exhaust stream. Low O2S voltage indicates a lean exhaust stream. If the PCM detects that HO2S 2 voltage stays below a specified value, DTC P1137 will set.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0172, P0201-P0204, P0300, P0301-P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P1441 are not set. |
| • | The ECT Sensor parameter is more than 70°C (158°F). |
| • | The Ignition 1 Signal parameter is more than 10 volts. |
| • | The Engine Run time parameter is more than 10 seconds. |
| • | The Power Enrichment parameter is Active. |
| • | The Loop Status parameter is closed. |
| • | The Fuel Level Sensor parameter is more than 10 percent. |
| • | The above conditions are met for 5 seconds. |
Conditions For Setting The DTC
The PCM detects that the O2S 1 parameter is more than 700 mV and the HO2S 2 parameter is less than 399 mV for 9.5 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. |
Diagnostic Aids
Inspect for the following conditions:
| • | A sensor pigtail may be mispositioned and contacting the exhaust manifold. |
| • | An intermittent ground in wire between the connector and the sensor. |
| • | A poor PCM ground |
| • | Lean injectors--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 . |
| • | Fuel Contamination--Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can also set this DTC. |
| • | Fuel pressure--If the pressure is too low, the system will be lean. In order to confirm, monitor a fuel pressure gauge while driving the vehicle at various speeds and loads. Refer to Fuel System Diagnosis . |
| • | Exhaust leaks--If there is an exhaust leak, the engine may pull the outside air into the exhaust and past the sensor. Refer to Exhaust Leakage in Engine Exhaust. |
| • | Vacuum or crankcase ventilation system leaks can cause a lean condition or possibly a high idle. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the DTC is the result of a hard malfunction or an intermittent condition.
-
It is necessary to jump the HO2S 2 low signal circuit to ground in order to allow the PCM to display the supplied bias voltage. The PCM and the wiring are OK if the voltage is between 350-550 mV.
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-Engine Controls? | -- | Go to Step 2 | |||||
Is the HO2S 2 voltage less than the specified value? | 200 mV | Go to Step 4 | Go to Step 3 | |||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||
Does the scan tool indicate the HO2S 2 voltage within the specified value? | 350-550 mV | Go to Step 7 | Go to Step 5 | |||||
5 | Test the HO2S high signal circuit for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 6 | ||||
6 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | ||||
7 | Replace the HO2S 2 . Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | ||||
8 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 | ||||
9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
