P0151
DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1
Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) signal high and signal low circuits. When measured with a 10 megaohm digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the Bank 2 HO2S 1 voltage remains excessively low for an extended period of time, DTC P0151 will be set.
Conditions for Setting the DTC
- No related DTCs.
- The engine is operating in closed loop.
- Engine coolant temperature is above 60 °C (140 °F).
- Closed loop commanded air/fuel ratio is between 14.5 and 14.8.
- Throttle angle is between 3% and 19%.
- Bank 2 HO2S 1 signal voltage remains below 22 mV during normal closed loop operation for a total of 77 seconds over a 90-second period of time.
Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected.
- The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.
- Open loop fuel control will be in effect.
Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history DTC P0151 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC Pal 51 can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.
Diagnostic Aids
Check for the following conditions:
- Heated oxygen sensor wiring - The sensor pigtail may be mispositioned and contacting the exhaust system.
- Poor PCM to engine block grounds.
- Fuel pressure - The system will go lean if pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, a DTC P0151 may be set. Refer to Fuel System Diagnosis. Refer Non-Trouble Code Diagnostic Procedures.
- Lean injector(s) - Perform Injector Balance Test.
- Vacuum leaks - Check for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, throttle body, EGR system, and PCV system.
- Exhaust leaks - An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing the system to appear lean. Check for exhaust leaks that may cause a false lean condition to be indicated.
- MAF sensor -The system can go lean if the MAF sensor signal indicates an engine airflow measurement that is not correct. Disconnect the MAF sensor to see if the lean condition is corrected. If so, replace the MAF sensor.
- Fuel contamination - Water, even in small amounts, can be delivered to the fuel injectors. The water can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Fuel System Diagnosis for the procedure to check for fuel contamination.
- If none of the above conditions are present, replace the affected HO2S.
Steps 1 - 5:
Steps 6 - 9:
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
3. DTC P0151 failing during operation may indicate a condition described in the Diagnostic Aids above. If the DTC P0151 test passes while the Failure Records conditions are being duplicated, an intermittent condition is indicate.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.