DTC P0131 or P0151. GMC Truck GMC C-Series Medium Duty Truck C6/C7/C8 2002

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C-Series Medium Duty Truck C6/C7/C8 🢒 DTC 🢒 DTC P0131 or P0151

Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM circuitry that monitors the HO2S, generates a reference, or bias, voltage of 450 mV when the sensor is cold, high resistance. Once the HO2S warms up, the HO2S generates a voltage within a range of 0-1000 mV, depending on the exhaust gas oxygen content. High HO2S voltage output indicates a rich fuel mixture. Low HO2S voltage output indicates a lean mixture. Once fueling goes Closed Loop, the HO2S voltage will fluctuate above and below the bias voltage. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.

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

Lean Test Enable

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.

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

•	The ignition voltage is between 11-18 volts.

•	The fuel system is operating in Closed Loop.

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

•	The fuel level is more than 10 percent.

Power Enrichment Test Enable

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.

•	The AIR and the EGR diagnostics are not active.

•	The ignition voltage is between 11-18 volts.

•	The fuel system is operating in Closed Loop.

•	The fuel level is above 10 percent.

•	The power enrichment (PE) mode is enabled for more than 1 second.

Conditions for Setting the DTC

Lean Test

•	The HO2S signal voltage remains below 200 mV.

•	The Lean Test Enable conditions are present for 400 seconds.

Power Enrichment Test

•	The HO2S signal voltage remains below 360 mV.

•	The Power Enrichment Test Enable conditions are present for 10 seconds during the PE mode.

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.

Test Description

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

This step checks for a shorted HO2S high signal circuit.

This step checks for an open HO2S low signal circuit.

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 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 Intermittent Conditions

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, measure the voltage of the HO2S high signal circuit for the sensor 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

Turn OFF the ignition.
Connect a 3-amp fused jumper wire between the HO2S high signal circuit and the HO2S low signal circuit at the engine side.
Turn ON the ignition, with the engine OFF.
Using a scan tool, observe the voltage of the affected sensor.

Does the voltage measure less than the specified value?

20 mV

Go to Step 8

Go to Step 7

Test the HO2S high signal circuit for a short to ground or short to the HO2S low reference. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 10

Test the HO2S low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 10

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 13

Go to Step 9

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 13

Go to Step 11

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 13

Go to Step 12

Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination.

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 13

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 13

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 14

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