DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 w/o RPO OSG
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, down 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 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
| • | No active mass air flow (MAF) DTCs |
| • | No active intake air temperature (IAT) DTCs |
| • | No active engine coolant temperature (ECT) DTCs |
| • | No active throttle position (TP) DTCs |
| • | No active injector DTCs |
| • | No active crank sensor DTCs |
| • | No active ignition control DTCs |
| • | The ignition voltage is more than 9 volts. |
| • | The fuel system operating in Closed Loop. |
| • | The fuel trim learn is enabled. |
| • | The secondary air injection (AIR), exhaust gas recirculation (EGR), and the catalyst diagnostics are not active. |
| • | The TP angle is between 2 percent and 70 percent. |
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 (MIL) 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 OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
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.
| • | Heated oxygen sensor (HO2S) wire -- The 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 Heated Oxygen Sensor Wiring Repairs in Wiring Systems. |
| • | Check for an intermittent ground in the signal wire between the connector and the sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | Lean injectors -- Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | 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 pressure -- System will be lean if the fuel pressure is low. Refer to Fuel System Diagnosis |
| • | Exhaust leaks -- An exhaust leak near the HO2S can cause a lean condition. Refer to Exhaust System Inspection in Engine Exhaust. |
| • | 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 .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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.
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Using the Freeze Frame and Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and 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 or a fail. Operate the vehicle within the same Freeze Frame conditions such as RPM, load, vehicle speed, temperature, etc. that the PCM recorded. This will isolate when the DTC failed.
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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.
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Disconnecting the PCM allows using the DMM in order to test continuity of the circuits. This aids in locating an open or shorted circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
|
Important: Inspect the HO2S for being secure before proceeding with this DTC. A sensor that is loose could cause this DTC to set.
Is the HO2S voltage less than the specified value? | 200 mV | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||
Does the scan tool indicate the HO2S voltage within the specified range? | 350-550 mV | Go to Diagnostic Aids | ||
Is the HO2S signal circuit shorted? | -- | |||
6 | Repair the HO2S signal circuit. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
7 |
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
8 |
Does the scan tool indicate that this test ran and passed? | -- | ||
9 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 w/ RPO OSG
Circuit Description
The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature and to maintain the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. Once the HO2S has reached operating temperature, the control module monitors the HO2S bias, or reference, voltage as well as the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel or enrich the mixture when the HO2S detects a lean exhaust content and subtract fuel, or lean-out the mixture when the HO2S detects a rich exhaust condition.
Certain vehicle models utilize an oxygen sensor after the catalytic converter in order to monitor catalyst efficiency.
This diagnostic trouble code (DTC) determines if the HO2S is functioning properly by checking for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the powertrain control module (PCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are listed below:
| • | An open or a short to voltage on either the HO2S signal or HO2S low circuits |
| • | A malfunctioning HO2S |
| • | A problem in the HO2S heater or its circuit |
| • | A poor HO2S ground |
| • | An open HO2S low reference circuit |
This DTC is designed to detect an HO2S voltage that remains low voltage for more than 100 seconds during a 120 second test period. This DTC is set under the following conditions:
| • | There is an HO2S circuit that results in a false lean exhaust condition. |
| • | The HO2S is correctly detecting the lean air/fuel ratio resulting from either a vacuum leak or a fuel control system problem. |
Conditions for Running the DTC
| • | No active throttle position (TP) sensor DTCs |
| • | No active evaporative emission (EVAP) system DTCs |
| • | No active intake air temperature (IAT) sensor DTCs |
| • | No active manifold absolute pressure (MAP) sensor DTCs |
| • | No active engine coolant temperature (ECT)sensor DTCs |
| • | No active mass air flow (MAF) sensor DTCs |
| • | No active misfire DTCs |
| • | No intrusive tests such as EGR or Catalyst in progress |
| • | No device control active |
| • | The system voltage is between 11.7-18 volts. |
Lean Test
| • | System in Closed Loop |
| • | The air/fuel ratio is between 14:5-14:8. |
| • | The throttle position is between 3.5-99 percent. |
Power Enrichment Lean Test
| • | System in Closed Loop |
| • | Power Enrichment mode is active |
| • | High speed fuel cut-off not active |
| • | The elapsed time since test enabled is more than 2 seconds. |
Conditions for Setting the DTC
Lean Test
The heated oxygen sensor (HO2S) voltage is less than 26 mV for more than 110 seconds.
Power Enrichment Lean Test
The HO2S voltage is less than 399 mV for more than 40 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
Important: Never solder the HO2S wires. For proper wire and connector repair, refer to Wiring Repairs in Wiring Systems.
Using the scan tool, observe the long term fuel trim values at the different RPM and the air flow conditions. The scan tool also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells in order to determine when the DTC may have set. If the conditions for this DTC exist, the long term fuel trim values measure around 158 or more.
Check for the following conditions:
| • | A sensor pigtail may be mispositioned and contacting the exhaust system. |
| • | 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 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. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | Fuel pressure -- If the pressure is too low, the system will be lean. In order to confirm, monitor a fuel pressure 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 System Inspection in Engine Exhaust. |
| • | Vacuum or crankcase leaks can cause a lean condition or a possibly high idle. |
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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In order to determine if the engine is lean during power enrichment, operate the vehicle under higher throttle and acceleration conditions while monitoring the scan tool HO2S voltage and the power enrichment parameter. A lean condition will cause HO2S voltage to be less than 598 mV during power enrichment.
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Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor, check for lean conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S needs replacement or a lean condition exists only on the suspect HO2S cylinder bank.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||||||||||
2 |
Is the HO2S voltage fixed less than the value specified? | 26 mv | ||||||||||||||||||||||||
The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Did you find a problem? | -- | Go to Diagnostic Aids | ||||||||||||||||||||||||
4 |
Is the HO2S voltage within the specified value range? | 351-551 mV | ||||||||||||||||||||||||
Did you find a problem? | -- | |||||||||||||||||||||||||
6 |
Is the resistance at the specified value on both tests? | ∞ | ||||||||||||||||||||||||
7 | Repair the HO2S signal HIGH circuit shorted to ground or shorted to the HO2S LOW circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||||||||||||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 2 . Is the action complete? | -- | -- | |||||||||||||||||||||||
9 |
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |||||||||||||||||||||||
10 |
Does the scan tool indicate that this diagnostic Passed? | -- | ||||||||||||||||||||||||
11 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
