Diagnostic Trouble Code (DTC)
P0131 HO2S (Sensor 1) Low Voltage
P0137 HO2S (Sensor 2) Low Voltage
Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
Conditions for Running the DTC
- Ignition switch is ON.
- Vehicle is in closed loop condition.
- No failure in HO2S heater.
- Engine speed is below 6016 rpm.
- Mass Air Flow (MAF) is higher than MAF diagnosis table.
Conditions for Setting the DTC
(P0131)
- HO2S signal voltage is lower than 24 mV for 10 seconds.
Or,
- HO2S signal voltage is between 352 mV and 499 mV for 10 seconds.
(P0137)
- HO2S signal voltage is lower than 24 mV for 40 seconds.
Or,
- HO2S signal voltage is between 352 mV and 499 mV for 10 seconds.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. The information will be stored in the freeze frame and failure records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The MIL will turn off at the end of a consecutive validation cycle in which the diagnostic runs without a fault.
- A history DTC will clear after 40 warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
Normal scan tool voltage varies between 0.1volts and 0.9 volts while in closed loop.
Inspect the oxygen sensor wire. The oxygen sensor may be positioned incorrectly and contacting the exhaust manifold. Check for an intermittent ground in the wire between the oxygen sensor and the engine control module.
Perform an injector balance test to determine if a restricted fuel injector may be causing the lean condition.
Vacuum of crankcase leaks will cause a lean running condition.
An exhaust manifold gasket leak of a cracked exhaust manifold may cause outside air to be pulled into the exhaust and past the sensor.
DTC P0131 - HO2S (Sensor 1) Low Voltage
DTC P0137 - HO2S (Sensor 2) Low Voltage
| Step | Action | Value(s) | Yes | No |
| 1 | Perform the Diagnostic System Check. Is the system check complete? | - | Go to Step 2 | |
| 2 | - Start the engine.
- Allow the engine to reach the normal operating temperature.
- Operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle.
- Observe the Loop Status parameter with a scan tool.
Does the scan tool display Closed Loop? | - | Go to Step 3 | Go to Step 4 |
| 3 | - Observe the Freeze Frame/Failure Records for this DTC.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 4 | |
| 4 | - Turn OFF the ignition.
- Disconnect the heated oxygen sensor (HO2S).
- Start the engine.
- Observe the HO2S voltage parameter with a scan tool.
Is the voltage within the specified range? | 350~550 mV | Go to Step 6 | Go to Step 5 |
| 5 | Test the signal circuit of the HO2S for a short to ground or an open. Did you find and correct the condition? | - | Go to Step 11 | Go to Step 8 |
| 6 | Test or inspect for the following conditions: - Lean fuel injectors.
- Low fuel system pressure.
- Fuel that is contaminated.
- Exhaust leaks near the HO2S.
- Engine vacuum leaks.
Did you find and correct the condition? | - | Go to Step 11 | Go to Step 7 |
| 7 | Test for an intermittent and poor connections at the harness connector of the HO2S. Did you find and correct the condition? | - | Go to Step 11 | Go to Step 9 |
| 8 | Test for an intermittent and poor connection at the engine control module (ECM). Did you find and correct the condition? | - | Go to Step 11 | Go to Step 10 |
| 9 | Replace the HO2S. Did you complete the replacement? | - | Go to Step 11 | - |
| 10 | Replace the ECM. Did you complete the replacement? | - | Go to Step 11 | - |
| 11 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 12 |
| 12 | Check if any additional DTCs are set. Are there any DTCs that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC)
P0132 HO2S (Sensor 1) High Voltage
P0138 HO2S (Sensor 2) High Voltage
Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
Conditions for Running the DTC
Conditions for Setting the DTC
- HO2S signal voltage is higher than 1.403 V.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. The information will be stored in the freeze frame and failure records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The MIL will turn off at the end of a consecutive validation cycle in which the diagnostic runs without a fault.
- A history DTC will clear after 40 warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
Normal scan tool voltage varies between 0.1volts and 0.9 volts while in closed loop.
Inspect the oxygen sensor wire. The oxygen sensor may be positioned incorrectly and contacting the exhaust manifold. Check for an intermittent ground in the wire between the oxygen sensor and the engine control module.
Perform an injector balance test to determine if a restricted fuel injector may be causing the lean condition.
Vacuum of crankcase leaks will cause a lean running condition.
An exhaust manifold gasket leak of a cracked exhaust manifold may cause outside air to be pulled into the exhaust and past the sensor.
DTC P0132 - HO2S (Sensor 1) High Voltage
DTC P0138 - HO2S (Sensor 2) High Voltage
| Step | Action | Value(s) | Yes | No |
| 1 | Perform the Diagnostic System Check. Is the system check complete? | - | Go to Step 2 | |
| 2 | - Start the engine.
- Allow the engine to reach the normal operating temperature.
- Operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle.
- Observe the Loop Status parameter with a scan tool.
Does the scan tool display Closed Loop? | - | Go to Step 3 | Go to Step 4 |
| 3 | - Observe the Freeze Frame/Failure Records for this DTC.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 4 | |
| 4 | - Turn OFF the ignition.
- Disconnect the heated oxygen sensor (HO2S).
- Start the engine.
- Observe the HO2S voltage parameter with a scan tool.
Is the voltage within the specified range? | 350~550 mV | Go to Step 6 | Go to Step 5 |
| 5 | Test the HO2S signal circuit for a short to voltage. Did you find and correct the condition? | - | Go to Step 11 | Go to Step 8 |
| 6 | Test or inspect for the following conditions: - HO2S harness connector for water intrusion.
- High fuel system pressure.
- Rich fuel injectors or fuel injectors that are leaking.
- Fuel saturation of the evaporative emission (EVAP) canister.
Did you find and correct the condition? | - | Go to Step 11 | Go to Step 7 |
| 7 | Test for shorted terminals and for poor connections at the harness connector of the HO2S. Did you find and correct the condition? | - | Go to Step 11 | Go to Step 9 |
| 8 | Test for shorted terminals and for poor connections at the harness connector of the engine control module (ECM). Did you find and correct the condition? | - | Go to Step 11 | Go to Step 10 |
| 9 | Replace the HO2S. Did you complete the replacement? | - | Go to Step 11 | - |
| 10 | Replace the ECM. Did you complete the replacement? | - | Go to Step 11 | - |
| 11 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 12 |
| 12 | Check if any additional DTCs are set. Are there any DTCs that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) P0133
HO2S (Sensor 1) Poor Performance
Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
Conditions for Running the DTC
- Vehicle is in closed loop condition.
- EVAP canister purge opening is less than 100%.
- Engine Coolant Temperature (ECT) is higher than 69.75°C (157.55°F).
- Vehicle speed is between 65 km/h (40.4 mph) and 75 km/h (46.6 mph).
- Engine speed is between 1888 rpm and 2400 rpm.
- Air flow is between 20 kg/h and 60 kg/h.
- No related malfunction exists.
Conditions for Setting the DTC
- Average HO2S periods are higher than 1.05/1.05 seconds (Rich / Lean each).
- Difference between rich and lean time is higher than 1.98 (lean to rich) or less than -1.98 (rich to lean).
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. The information will be stored in the freeze frame and failure records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The MIL will turn off at the end of 3 consecutive validation cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
If any DTCs are set, except P0133, refer to those DTCs before proceeding with this diagnostic table.
Test Description
The number(s) below refer(s) to the step numbers on the diagnostic table.
- This step determines if the condition is present. This test may take 5-10 minutes for the diagnostic to run.
- An exhaust leak 15-30 cm (6-12 inches) away from the HO2S can cause a DTC to set.
- Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can also cause silicone contamination. If the sensors appear contaminated by silicone, and if all the silicone sealant is a non-silicone base, advise the customer to try a different fuel company. A missing fuel filler restrictor indicates that the customer may have used leaded fuel.
DTC P0133 - HO2S (Sensor 1) Poor Performance
| Step | Action | Value(s) | Yes | No |
| 1 | Perform the Diagnostic System Check. Is the system check complete? | - | Go to Step 2 | |
| 2 | - Allow the engine to reach the normal operating temperature.
- Operate the vehicle within the parameters specified in Conditions for Running the DTC.
- Observe the diagnostic trouble code (DTC) information with a scan tool.
Did the DTC fail this ignition? | - | Go to Step 4 | Go to Step 3 |
| 3 | - Observe the Freeze Frame/Failure Records for this DTC.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 4 | |
| 4 | Inspect for an exhaust leak near the HO2S. Did you find and correct the condition? | - | Go to Step 7 | Go to Step 5 |
| 5 | Inspect or test for the following conditions: - The HO2S is securely installed.
- Inspect for corrosion on the HO2S terminals.
- Inspect the terminal tension at the HO2S and at the ECM.
- Inspect the HO2S wiring for damage.
- Fuel that is contaminated.
- Inspect for the correct RTV sealant.
- Inspect for engine oil consumption.
- Inspect for engine coolant consumption.
Did you find and correct the condition? | - | Go to Step 7 | Go to Step 6 |
| 6 | Replace the HO2S. Did you complete the replacement? | - | Go to Step 7 | - |
| 7 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 8 |
| 8 | Check if any additional DTCs are set. Are there any DTCs that have not been diagnosed? | - | Go to applicable DTC table | System OK |
Diagnostic Trouble Code (DTC) P0140
HO2S (Sensor 2) Circuit or Signal Fault
Circuit Description
The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the low reference circuit. The HO2S 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 ECM monitors and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The ECM 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.
Conditions for Running the DTC
- During catalyst deterioration monitoring.
Conditions for Setting the DTC
- The ECM detects the HO2S functionality by checking switch time counter.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The ECM will record operating conditions at the time the diagnostic fails. The information will be stored in the freeze frame and failure records buffers.
- A history DTC is stored.
Conditions for Clearing the MIL/DTC
- The MIL will turn off at the end of 3 consecutive validation cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 warm up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
- This step determines if the condition is present. This test may take 5-10 minutes for the diagnostic to run.
- This step tests the HO2S signal and the low reference circuit for a high resistance. The HO2S voltage should go low.
- An exhaust leak 6-12 inches away from the HO2S can cause a DTC to set.
- Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can also cause silicone contamination. If the sensors appear contaminated by silicone, and if all the silicone sealant is a non-silicone base, advise the customer to try a different fuel company. A missing fuel filler restrictor indicates that the customer may have used leaded fuel.
DTC P0140 – HO2S (Sensor 2) Circuit or Signal Fault
| Step | Action | Value(s) | Yes | No |
| 1 | Did you perform the Diagnostic System Check? | - | Go to Step 2 | |
| 2 | Important : If any DTCs are set, except for P0140, refer to those DTCs before proceeding with this diagnostic table. - Allow the engine to reach the normal operating temperature.
- Operate the vehicle within the parameters specified in Conditions for Running the DTC.
- Observe the diagnostic trouble code (DTC) information with a scan tool.
Did the DTC P0140 fail this ignition? | - | Go to Step 4 | Go to Step 3 |
| 3 | - Observe the Freeze Frame/Failure Records for this DTC.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 4 | |
| 4 | - Turn OFF the ignition.
- Disconnect the harness connector of the affected heated oxygen sensor (HO2S).
- Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S.
- Start the engine.
- Observe the HO2S voltage parameter with a scan tool.
Is the voltage less than the specified value? | 20 mV | Go to Step 8 | Go to Step 5 |
| 5 | - Connect a 3-amp fused jumper wire between the HO2S signal circuit and a good ground.
- Observe the HO2S voltage parameter with a scan tool.
Is the voltage less than the specified value? | 20 mV | Go to Step 7 | Go to Step 6 |
| 6 | Test the HO2S signal circuit for high resistance. Did you find and correct the condition? | - | Go to Step 13 | Go to Step 10 |
| 7 | Test the HO2S low reference circuit for high resistance. Did you find and correct the condition? | - | Go to Step 13 | Go to Step 10 |
| 8 | Inspect for an exhaust leak near the HO2S. Did you find and correct the condition? | - | Go to Step 13 | Go to Step 9 |
| 9 | Inspect or test for the following conditions: - The HO2S is securely installed.
- Inspect for corrosion on the HO2S terminals.
- Inspect the terminal tension at the HO2S and at the ECM.
- Inspect the HO2S wiring for damage.
- Fuel that is contaminated.
- Inspect for the correct RTV sealant.
- Inspect for engine oil consumption.
- Inspect for engine coolant consumption.
Did you find and correct the condition? | - | Go to Step 13 | Go to Step 11 |
| 10 | Test for shorted terminals and for poor connections at the harness connector of the engine control module (ECM). Did you find and correct the condition? | - | Go to Step 13 | Go to Step 12 |
| 11 | Replace the appropriate HO2S. Did you complete the replacement? | - | Go to Step 13 | - |
| 12 | Replace the ECM. Did you complete the replacement? | - | Go to Step 13 | - |
| 13 | - Clear the DTCs with a scan tool.
- Turn OFF the ignition for 30 seconds.
- Start the engine.
- Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition? | - | Go to Step 2 | Go to Step 14 |
| 14 | Check if any additional DTCs are set. Are there any DTCs that have not been diagnosed? | - | Go to applicable DTC table | System OK |
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