Circuit Description
The powertrain control module (PCM) supplies a voltage of about 450 mV between the heated oxygen sensor (HO2S) high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, through about 10 mV when the exhaust is lean. The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period, and determines if the majority of the samples are out of the operating range. The PCM monitors the HO2S voltage for being fixed below a predetermined voltage. If the PCM detects the voltage is below a predetermined voltage, a diagnostic trouble code (DTC) sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0300, P0351, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1258, P1404, or P1441 are not set. |
| • | The TP sensor is between 3-70 percent. |
| • | The loop status is closed. |
| • | The fuel tank level remaining is more than 10 percent. |
| • | The ignition 1 signal is between 9-18 volts. |
Conditions for Setting the DTC
| • | The HO2S signal voltage remains below 26 mV. |
| • | The above conditions are met for 110 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
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
| • | Inspect the HO2S wire. The sensor pigtail may be in contact with the exhaust manifold or with the exhaust system. |
| • | Check the HO2S oxygen supply. An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor (HO2S) Wiring Repairs in Wiring Systems. |
| • | Check for an intermittent ground in the signal wire between the connector and the sensor. Refer to Intermittent and Poor Connections in Wiring Systems. |
| • | Inspect the lean injectors. Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | Check for fuel contamination. Water near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC. Refer to Fuel Injector Balance Test with Tech 2 . |
| • | Check the fuel pressure. The system will be lean if the fuel pressure is low. Refer to Fuel System Diagnosis . |
| • | Check for exhaust leaks. An exhaust leak near the HO2S can cause a lean condition. Refer to Exhaust Leakage in Engine Exhaust. |
| • | Check for vacuum leaks or for crankcase leaks that can cause a lean condition. |
| • | If the components listed above are OK, the HO2S may be at fault. |
For an intermittent condition, refer to Symptoms - Engine Controls .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the voltage is below the specified value the condition is present.
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Jumpering the HO2S low signal circuit to ground is necessary for the PCM to correctly measure the voltage on the HO2S high signal circuit. If the HO2S voltage is within the specified range, the PCM and HO2S high signal circuit are OK.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
|
Important: With the engine running, observe the front HO2S voltage using a scan tool. If the front HO2S voltage is fixed above 900 mV, refer to DTC P0132 or P0152 .
Is the HO2S voltage less than the specified value? | 26 mV | Go to Step 4 | Go to Step 3 | |||||||||||||
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||
Is the HO2S voltage within the specified range? | 350-550 mV | Go to Step 5 | Go to Step 6 | |||||||||||||
5 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | ||||||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7 | ||||||||||||
7 | Test the HO2S high signal circuit for a short to the HO2S Low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||||||
8 | Inspect for poor connections at the harness connector of the HO2S. Refer to Intermittent and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||||||||
9 | Inspect for poor connections at the harness connector of the PCM. Refer to Intermittent and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||||||
10 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or to Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||
