DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2 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 above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a diagnostic trouble code (DTC) sets.
Conditions for Running the DTC
Criteria 1
| • | 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 9.0 volts. |
| • | The fuel system is operating in Closed Loop. |
| • | The secondary air injection (AIR), exhaust gas recirculation (EGR), and the catalyst diagnostics are not active. |
| • | The fuel trim learn is enabled. |
| • | The TP angle is between 2 percent and 70 percent. |
OR
Criteria 2
| • | No active MAF DTCs |
| • | No active IAT DTCs |
| • | No active ECT DTCs |
| • | No active TP DTCs |
| • | No active injector DTCs |
| • | No active crank sensor DTCs |
| • | No active ignition control DTCs |
| • | The ignition voltage is more than 9.0 volts. |
| • | The AIR, EGR, and the Catalyst diagnostics are not active. |
| • | The Deceleration Fuel Cut-off mode is enabled for more than 3.0 seconds. |
Conditions for Setting the DTC
Criteria 1
| • | The HO2S signal voltage remains above 930 mV. |
| • | The Criteria 1 conditions are present for 40 seconds. |
OR
Criteria 2
| • | The HO2S signal voltage remains above 480 mV for 4.5 seconds. |
| • | The Criteria 2 conditions are present for 5 seconds during the Deceleration Fuel Cut-off mode. |
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.
| • | Check the HO2S electrical connections for evidence of water intrusion. Water present in the connector causes the B+ supply to the heater to bleed over to the signal circuit. |
| • | Fuel pressure -- The system goes rich if the pressure is too high. The PCM compensates for some increase. However, if the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis . |
| • | Rich injectors -- Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | Leaking injector -- Refer to the Fuel System Diagnosis . Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | Fuel pressure regulator -- Inspect the vacuum line going to the fuel pressure regulator for evidence of fuel. Refer to the Fuel System Diagnosis . |
| • | Evaporative emissions (EVAP) canister purge -- Check the canister for fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission Control System Operation Description . |
| • | MAF sensor --Disconnect the MAF sensor and see if the rich condition is corrected. If so, check for proper installation. If installed correctly, replace the MAF sensor. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows cast into it indicating proper air flow direction. The arrows must point toward the engine. |
| • | 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. |
| • | TP sensor -- An intermittent TP sensor output causes the system to go rich, due to a false indication of the engine accelerating. 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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This DTC also sets during a deceleration fuel cut-off. Inspect items which could cause a rich exhaust during a deceleration such as leaking injectors, stuck injectors etc. Refer to the Conditions for Setting the DTC.
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 duplicated 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 you observed. This will isolate when the DTC failed.
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If the voltage remains high, this indicates the signal circuit is shorted to a voltage. If the voltage goes low, this indicates a rich condition.
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This step isolates the condition. If the voltage remains high, this indicates the signal circuit is not shorted to the heater positive voltage circuit.
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Review the system mechanization. Test for a short between the HO2S signal circuit and any other wires powered by this fuse that run together inside the harness.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
|
Important: Inspect the front HO2S voltage before proceeding with this DTC. If the front HO2S voltage is fixed below 300 mV, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 .
Is the HO2S voltage more than the specified value? | 930 mV | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||
Is the HO2S voltage more than the specified value? | 930 mV | Go to Diagnostic Aids | ||
Remove the HO2S heater fuse while monitoring the HO2S voltage. Does the voltage drop to within the specified range when the power to the heater is disconnected? | 350-550 mV | |||
6 |
Does the scan tool indicate the HO2S voltage is within the specified range? | 350-550 mV | ||
7 |
Important: Disconnecting the PCM may eliminate the short to voltage if the signal circuit is shorted to another C1 circuit.
Is there any voltage present? | -- | ||
Repair the short to voltage in the HO2S signal circuit. Refer to Wiring Repairs in Wiring Systems. 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 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 . Is the action complete? | -- | -- | |
11 |
Does the scan tool indicate that this test ran and passed? | -- | ||
12 | 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 P0138 HO2S Circuit High Voltage Bank 1 Sensor 2 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 at a high voltage for more than a specified number of seconds during the test conditions. This DTC is set under the following conditions:
| • | There is an HO2S circuit fault that results in a false rich exhaust condition. |
| • | The HO2S is correctly detecting a rich air/fuel ratio resulting from either a fuel control or emission system fault. |
Conditions for Running the DTC
| • | No active throttle position (TP) sensor DTCs |
| • | No active evaporative emission (EVAP) DTCs |
| • | No active intake air temperature (IAT) sensor DTCs |
| • | No active mass air flow (MAP) sensor DTCs |
| • | No active engine coolant temperature (ECT) sensor DTCs |
| • | No active manifold absolute pressure (MAF) sensor DTCs |
| • | No intrusive test in progress |
| • | No device controls active |
| • | The system voltage is between 11.7-18 volts. |
Rich Test Enable
| • | The system is in Closed Loop. |
| • | The air/fuel ratio is between 14:5-14:8. |
| • | The throttle position is between 0-50 percent. |
| • | The above conditions are met for 5 seconds. |
DFCO Rich Test Enable
| • | Decel fuel cutoff mode is active |
| • | The system is in Closed Loop. |
| • | The elapsed time since the test enabled is more than 2 seconds. |
Conditions for Setting the DTC
Rich Test
The heated oxygen sensor (HO2S) voltage is more than 976 mV for more than 40 seconds.
DFCO Rich Test
The HO2S voltage is more than 468 mV for more than 30 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 or Connector Repairs in Wiring Systems.
Check the following items:
| • | The fuel pressure -- If the pressure is too high, the system will run rich. The PCM can compensate for some increase; however, if the pressure gets too high, this DTC may set. Refer to Fuel System Diagnosis . |
| • | A rich injector -- Perform an Injector Balance test. Refer to Fuel Injector Balance Test with Tech 2 . |
| • | A leaking injector -- Refer to Fuel System Diagnosis . |
| • | Fuel contaminated oil |
| • | EVAP canister purge -- Check for a fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission Control System Operation Description . |
| • | Leaking fuel pressure regulator diaphragm by checking the vacuum line to the regulator for fuel. |
| • | The TP sensor -- An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving. |
| • | False rich indication due to silicon contamination of the heated oxygen sensor -- This DTC, accompanied by a lean driveability condition and a powdery white deposit on the sensor, may indicate a false rich condition. |
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 rich during De-acceleration Fuel Cut-Off (DFCO), operate the vehicle up to highway speed conditions and release the accelerator pedal allowing the vehicle to coast in gear. Monitor the scan tool HO2S voltage and the DFCO parameter. A rich condition will cause HO2S voltage to be above 468 mV during DFCO.
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
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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 rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.
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An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check ? | -- | ||||||||||||||||||||||||
2 |
Is the HO2S voltage fixed more than the value specified? | 976 mV | ||||||||||||||||||||||||
Did you find a problem? | -- | Go to Diagnostic Aids | ||||||||||||||||||||||||
4 |
Is the HO2S voltage within the value range specified? | 351-551 mV | ||||||||||||||||||||||||
Did you find a problem? | -- | |||||||||||||||||||||||||
6 |
Is the voltage more than the specified value? | 20 mV | ||||||||||||||||||||||||
7 | Repair the short to voltage in the HO2S HIGH signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||||||||||||
|
Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination. Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 . 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 |
Important: If a rich engine condition was repaired inspect the engine oil for fuel contamination and replace engine oil as necessary. Did this DTC run and pass? | -- | System OK |
