P0151

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 1,000 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 sets.

Conditions for Running the DTC
^ DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358, P1258 not set.
^ The ignition voltage is greater than 9.0 volts.
^ The fuel system operating in Closed Loop.
^ The fuel trim learn is enabled.
^ The AIR, EGR, and the Catalyst diagnostics are not active.
^ The TP angle is between 2% and 70%.

Conditions for Setting the DTC
^ The HO2S signal voltage remains below 200 mV.
^ The conditions are present for 33 seconds.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure records.

Conditions for Clearing the MIL/DTC
^ The PCM turns the MIL OFF after three consecutive ignition cycles 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.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

^ 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.
^ Check for intermittent ground in signal wire between connector and sensor. Refer to Intermittents and Poor Connections Diagnosis.
^ Lean injector(s): Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool. Component Tests and General Diagnostics
^ 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 Alcohol/Contaminants-in-Fuel Diagnosis. Fuel Delivery and Air Induction
^ Fuel pressure: System will be lean if fuel pressure is low. Refer to Fuel System Diagnosis.Component Tests and General Diagnostics
^ 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. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. If the HO2S voltage is fixed well below 200 mV, this indicates a short to battery ground or chassis ground. If the voltage is fixed near or above 200 mV, this indicates a short to a PCM ground.
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. Disconnecting the HO2S and grounding the low reference circuit should cause the HO2S voltage to display a bias voltage. If the voltage is low inspect the high reference signal circuit for a short to ground.
5. Disconnecting the PCM allows using the DMM J 39200 in order to test continuity of the circuits. This aids in locating an open or shorted circuit.