DTC P0131 or P0151. GMC Truck GMC C Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC P0131 or P0151

DTC P0131 or P0151 w/ Delphi HO2S

Circuit Description

This diagnostic applies only to vehicles built with Delphi heated oxygen sensors. In order to identify the heated oxygen sensor, refer to

Oxygen Sensor Identification (4.8L/5.3L/6.0L)


(1)	Delphi Sensor - Case Grounded
(2)	Denso Sensor - Isolated Grounded

in Engine Controls Component Views.

The powertrain control module (PCM) supplies a voltage of about 450 mV between the heated oxygen sensor (HO2S) high and low signal circuits. The HO2S varies the voltage over a range of about 1,000 mV when the exhaust is rich to 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

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1415, P1416, P1514, P1515, P1516, P1517, or P1518 are not set.

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

•	Vehicles without throttle-actuated control (TAC), the throttle position (TP) is between 3-70 percent.

•	Vehicles with throttle-actuated control (TAC), the throttle position (TP) indicated angle is between 3-70 percent more than the value observed at idle.

•	The loop status is closed.

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

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

•	Intrusive tests are not in progress.

•	The scan tool output controls are not active.

Conditions for Setting the DTC

The HO2S voltage is less than 200 mV for 165 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.

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.

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

•	Check the HO2S oxygen supply. An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and the connections for breaks and for 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.

•	Check the injectors. Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or to Fuel Injector Balance Test with Special Tool .

•	Check for contaminated fuel. 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 .

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

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

•	Check for vacuum leaks or for 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 Intermittent Conditions .

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

Value(s)

Yes

Schematic Reference: Engine Controls Schematics

Important: This diagnostic applies only to vehicles built with Delphi heated oxygen sensors. To identify the heated oxygen sensor, refer to

Oxygen Sensor Identification (4.8L/5.3L/6.0L)


(1)	Delphi Sensor - Case Grounded
(2)	Denso Sensor - Isolated Grounded

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?

200 mV

Go to Step 4

Go to Step 3

Observe the Freeze Frame and/or 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 and/or 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 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. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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 refer to 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

DTC P0131 or P0151 w/ Denso HO2S

Circuit Description

This diagnostic applies only to vehicles built with Denso heated oxygen sensors. In order to identify the heated oxygen sensor, refer to

Oxygen Sensor Identification (4.8L/5.3L/6.0L)


(1)	Delphi Sensor - Case Grounded
(2)	Denso Sensor - Isolated Grounded

in Engine Controls Component Views.

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

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0410, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1415, P1416, P1514, P1515, P1516, P1517, or P1518 are not set.

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

•	Vehicles without throttle-actuated control (TAC), the throttle position (TP) is between 3-70 percent.

•	Vehicles with throttle-actuated control (TAC), the throttle position (TP) indicated angle is between 3-70 percent more than the value observed at idle.

•	The loop status is closed.

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

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

•	Intrusive tests are not in progress.

•	The scan tool output controls are not active.

Conditions for Setting the DTC

The HO2S voltage is less than 200 mV for 165 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.

•

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: Never solder the HO2S wires. For proper wire and connection 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 short to ground in the signal circuit between the PCM connector and HO2S

•	A poor PCM to the engine block ground

•	Any lean injectors. Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 .

•	Any 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 .

•	The fuel pressure. If the pressure is too low, the system will be lean. In order to confirm the fuel pressure, monitor the fuel pressure while driving the vehicle at various speeds and loads. Refer to Fuel System Diagnosis .

•	Any 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 Leakage in Engine Exhaust.

•	Any vacuum or crankcase leaks can cause a lean condition or a 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 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

Important: This diagnostic applies only to vehicles built with Denso heated oxygen sensors. To identify the heated oxygen sensor, refer to

Oxygen Sensor Identification (4.8L/5.3L/6.0L)


(1)	Delphi Sensor - Case Grounded
(2)	Denso Sensor - Isolated Grounded

in Engine Controls Component Views.

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?

200 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 PCV valve or system

-	An incorrect fuel pressure

-	Any lean fuel injectors

-	An inaccurate 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.
Jumper the HO2S LOW reference circuit terminal to a ground.
Turn ON the ignition, leaving 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.
Remove the jumper from the HO2S reference low circuit.
Disconnect the PCM connector that contains the HO2S high signal circuit.
Use a digital multimeter (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 refer to 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