P0151

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION
The PCM supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean. The PCM monitors and stores the heated oxygen sensor (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if 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 DTC will set.

CONDITIONS FOR RUNNING THE DTC
Criteria 1
- DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0335, P0336, P0351-P0358, P1258 not set.
- The engine coolant temperature is greater than 48°C (118°F).
- The ignition voltage is greater than 9.0 volts.
- The fuel system operating in Closed Loop.
- The AIR, EGR, and the Catalyst diagnostics are not active.
- The fuel trim learn is enabled.
- The air/fuel ratio is between 14.5:1 and 14.7:1
- The TP angle is between 3% and 20%.
OR
Criteria 2
- DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0335, P0336, P0351-P0358, P1258 not set.
- The ignition voltage is greater than 9.0 volts.
- The AIR, EGR, and the Catalyst diagnostics are not active.
- The Power Enrichment mode is enabled for greater than 0.5 second.

CONDITIONS FOR SETTING THE DTC
Criteria 1
- The HO2S signal voltage remains below 200 mV.
- The Criteria 1 conditions are present for 33 seconds.
OR
Criteria 2
- The HO2S signal voltage remains below 360 mV.
- The Criteria 2 conditions are present for 5.0 seconds during the Power Enrichment mode.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the Malfunction Indicator Lamp when the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or the Failure Records.
- Open Loop Fueling.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
- A last test failed (current DTC) clears when the diagnostic runs and does not fail.
- A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
- The PCM battery voltage is interrupted.
- Use a scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS
- Heated Oxygen Sensor (HO2S) wire: Sensor pigtail may be in contact with the exhaust manifold or the exhaust system.
- An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provides the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Electrical Diagnosis Repair Procedures.
- Check for intermittent ground in signal wire between connector and sensor.
- Lean injector(s): Perform the Injector Balance Test. Fuel Injector Balance Test
- 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.
- Fuel pressure: System will be lean if fuel pressure is low. Refer to Fuel System diagnosis. System Diagnosis - Fuel System
- Exhaust leaks: An exhaust leak near the HO2S can cause a lean condition.
- Vacuum or crankcase leaks can cause a lean condition.
- If the above are OK, the HO2S may be at fault. For an intermittent condition, refer to Symptoms. Testing and Inspection

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. If the HO2S voltage is fix well below 200 mV, this indicates a short to battery ground or chassis ground. If the voltage is fix near or above 200 mV, this indicates a short to a PCM ground. When the HO2S voltage is fix near 200 mV, indicates the DTC set when the fuel system was in a Power Enrichment mode of operation. This DTC sets if the HO2S voltage is less than 360 mV during a Power Enrichment mode of operation.
The engine must be at the normal operating temperature before performing this test. For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A. Using this kit prevents damage to the harness connector terminals.
3. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you can not duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that the PCM recorded. This will isolate when the DTC failed.
4. Grounding the low side circuit of the HO2S should cause the HO2S voltage to display a bias voltage. A voltage staying near 0.0 volts indicates the low circuit is open, or the high circuit is open or grounded.
5. Disconnecting the PCM allows using a DMM J 39200 in order to check continuity of the circuits. This aids in locating an open or shorted circuit.