DTC P0131 or P0151. GMC Truck GMC K Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0131 or P0151

DTC P0131 or P0151 California W/ RPO LU3

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. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors 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. The control module will subtract fuel, or lean out the mixture, when the HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains low for more than a specified number of seconds during the test conditions.

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1404 or P1441 are not set.

•	The ignition 1 signal is between 9-18 volts.

•	The fuel tank level remaining is more than 10 percent.

•	The loop status is closed.

•	Intrusive tests are not in progress.

•	Scan tool output controls are not active.

Lean Test Enable

•	The air fuel ratio is between 14.5:1-14.7:1.

•	The throttle position (TP) is between 3-70 percent.

Power Enrichment Test Enable

•	Power enrichment is active.

•	The above condition is met for 2 second.

Conditions for Setting the DTC

Lean Test

The HO2S voltage is less than 99 mV for 99 seconds.

Power Enrichment Test

The HO2S voltage is less than 600 mV for 10 seconds.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

•

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

•	The control module commands Open Loop.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

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.

•	Inspect the heated oxygen sensor (HO2S) wire--The sensor pigtail may be in contact with the exhaust manifold or with the exhaust system.

•	An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and inspect the connections for breaks or for contamination--Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

•	Check for intermittent ground in the signal wire between the connector and the sensor--Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

•	Inspect for lean injectors. Perform the Injector Balance Test--Refer to Fuel Injector Balance Test with Tech 2 .

•	Inspect for 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 .

•	Inspect the fuel pressure--The system will be lean if fuel the pressure is low. Refer to Fuel System Diagnosis .

•	Inspect for exhaust leaks--An exhaust leak near the HO2S can cause a lean condition. Refer to Exhaust Leakage in Engine Exhaust.

•	Inspect for vacuum or crankcase leaks that can cause a lean condition.

•	If the above components are OK, the HO2S may be at fault.

For an intermittent condition, refer to Symptoms - Engine Controls .

Test Description

The number below refer to the step number on the diagnostic table.

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

Values

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Run the engine until the engine reaches the normal operating temperature.
Use a scan tool in order to monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage less than the specified value?

99 mV

Go to Step 4

Go to Step 3

The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:

•	A signal wire intermittently shorted to engine ground or to the HO2S low reference circuit

•	Any water intrusion into the HO2S connector

•	An exhaust leak between the HO2S and the engine. Refer to Exhaust Leakage in Engine Exhaust.

•	An intermittent lean engine condition such as the following:

-	A vacuum leak

-	An incorrect or defective positive crankcase ventilation (PCV) valve or system

-	An incorrect fuel pressure

-	Any lean fuel injectors

-	An inaccurate mass air flow (MAF) sensor

-	A lean engine condition during Power Enrichment operation

-	Repair any engine conditions as necessary.

Did you find and correct the condition?

Go to Step 10

Go to Diagnostic Aids

Turn OFF the ignition.
Disconnect the HO2S connector for the sensor that applies to this DTC.
Turn ON the ignition, with the engine OFF.
Use the scan tool in order to monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage within the specified range?

351-551 mV

Go to Step 5

Go to Step 6

The HO2S may be detecting a lean exhaust condition. Check for one of the following conditions:

•	Any water intrusion into the HO2S connector

•	An exhaust leak between the HO2S and the engine. Refer to Exhaust Leakage in Engine Exhaust.

•	Any vacuum leaks

•	An incorrect fuel pressure

•	Any lean fuel injectors

•	An inaccurate MAF sensor

Repair any engine conditions as necessary.

Did you find and correct the condition?

Go to Step 10

Go to Step 8

Turn OFF the ignition.
Disconnect the PCM connector that contains the HO2S high signal circuit.
Use a DMM in order to measure and record the resistance between the HO2S high signal circuit and ground.
Measure and record the resistance between the HO2S high signal circuit and the HO2S low reference circuit.

Is the resistance infinite on both circuits?

∞

Go to Step 9

Go to Step 7

Repair the HO2S signal high circuit for a short to ground or a short to the HO2S low reference circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 10

Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 .

Did you complete the replacement?

Go to Step 10

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 10

Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 11

Go to Step 2

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any additional undiagnosed DTCs?

Go to Diagnostic Trouble Code (DTC) List

System OK

DTC P0131 or P0151 Federal W/ RPO L35

Circuit Description

This DTC is designed to detect an HO2S voltage that remains low for more than a specified number of seconds during the test conditions.

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0405, P0440, P0442, P0452, P0453, P1404, or P1441 are not set.

•	The ignition 1 signal is between 9-18 volts.

•	The fuel tank level remaining is more than 10 percent.

•	The loop status is closed.

•	Intrusive tests are not in progress.

•	Scan tool output controls are not active.

Lean Test Enable

•	The air fuel ratio is between 14.5:1-14.7:1.

•	The throttle position (TP) is between 3-70 percent.

Power Enrichment Test Enable

•	Power Enrichment is active.

•	The above conditions are met for 2 seconds.

Conditions for Setting the DTC

Lean Test

The HO2S voltage is less than 87 mV for 180 seconds.

Power Enrichment Test

The HO2S voltage is less than 360 mV for 10 seconds.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

•

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

•	The control module commands Open Loop.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

•	Inspect the heated oxygen sensor (HO2S) wire--The sensor pigtail may be in contact with the exhaust manifold or with the exhaust system.

•	An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and inspect the connections for breaks or for contamination--Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

•	Check for intermittent ground in the signal wire between the connector and the sensor--Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

•	Inspect for lean injectors. Perform the Injector Balance Test--Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool .

•	Inspect for 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 .

•	Inspect the fuel pressure--The system will be lean if fuel the pressure is low. Refer to Fuel System Diagnosis .

•	Inspect for exhaust leaks--An exhaust leak near the HO2S can cause a lean condition. Refer to Exhaust Leakage in Engine Exhaust.

•	Inspect for vacuum or crankcase leaks that can cause a lean condition.

•	If the above components are OK, the HO2S may be at fault.

For an intermittent condition, refer to Symptoms - Engine Controls .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

If the voltage is below the specified value the condition is present.

Jumpering the HO2S low signal circuit to ground is necessary for the PCM to correctly measure the voltage on the HO2S high signal circuit. If the HO2S voltage is within the specified range, the PCM and HO2S high signal circuit are OK.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Allow the engine to reach operating temperature.
With a scan tool, observe the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage less than the specified value?

87 mV

Go to Step 4

Go to Step 3

Observe the Freeze Frame/Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

Turn OFF the ignition.
Disconnect the HO2S connector for the sensor that applies to this DTC.
Jumper the HO2S low signal circuit terminal on the engine harness side to a known good ground.
Turn ON the ignition, with the engine OFF.
Observe the HO2S voltage with a scan tool.

Is the HO2S voltage within the specified range?

350-550 mV

Go to Step 5

Go to Step 6

The HO2S may be detecting a lean exhaust condition. Check for the following conditions:

•	Water intrusion into the HO2S connector

•	Exhaust leak between the HO2S and the engine

•	Vacuum leaks

•	Incorrect fuel pressure

•	Lean fuel injectors

•	Inaccurate mass air flow (MAF) sensor

Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

Go to Step 12

Go to Step 8

Turn OFF the ignition.
Disconnect the PCM connector that contains the HO2S high signal circuit. Refer to Powertrain Control Module Replacement .
Test the HO2S high signal circuit for a short to ground.

Did you find and correct the condition?

Go to Step 12

Go to Step 7

Test the HO2S high signal circuit for a short to the HO2S Low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

Inspect for poor connections at the harness connector of the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 10

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 .

Did you complete the replacement?

Go to Step 12

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 12

Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 13

Go to Step 2

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK