DTC P0131 or P0151. GMC Truck Yukon

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon - 2WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0131 or P0151

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. Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor the catalyst efficiency.

This DTC is designed to detect an HO2S voltage that remains at a low voltage 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, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set.

•	The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active.

•	The ignition voltage is more than 9 volts.

•	The fuel system is operating in Closed Loop.

•	The fuel trim learn is enabled.

•	The accelerator pedal position (APP) indicated angle is between 3-70 percent.

Conditions for Setting the DTC

The HO2S signal voltage remains below 200 mV for 165 seconds or more.

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

Check for the following conditions:

•	The heated oxygen sensor (HO2S) wires--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 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 .

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

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

•	Vacuum or crankcase leaks can cause a lean condition.

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

For an intermittent, refer to Intermittent Conditions .

Test Description

The number below refers 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 a normal operating temperature.
Using the scan tool, monitor the HO2S voltage for the sensor that applies to this DTC.

Does the HO2S voltage measure less than the specified value?

86 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.

Did 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.
Turn ON the ignition, with the engine OFF.
Using a DMM, observe the voltage of the High Signal circuit for the HO2S that applies to this DTC.

Does the HO2S voltage measure 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 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.
Using a DMM, 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 10

Go to Step 7

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

Did you complete the repair?

Go to Step 12

Inspect for poor connections at the harness connector of the affected 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 9

Replace the 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

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 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 engine 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