DTC P0138 or P0158. Chevrolet Avalanche

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2002 🢒 Avalanche - 4WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0138 or P0158

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 high voltage for more than a specified number of seconds during the test conditions.

Conditions for Running the DTC

Rich 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 more than 9 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.

Decel Fuel Cut-off (DFCO) 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 more than 9 volts.

•	The fuel system is operating in Closed Loop.

•	The fuel level is more than 10 percent.

•	The decel fuel cut-off (DFCO) mode is enabled for more than 2 seconds.

Conditions for Setting the DTC

Rich Test

•	The HO2S signal voltage remains above 930 mV.

•	The criteria 1 conditions are present for 200 seconds.

DFCO Test

•	The HO2S signal voltage remains above 400 mV for 4.5 seconds.

•	The criteria 2 conditions are present for 4.5 seconds during the DFCO 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 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, test 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.

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

Important: With the engine running, observe the front HO2S voltage with a scan tool. If the front HO2S voltage is fixed above 200 mV, refer to DTC P0131 or P0151.

Run the engine until the engine reaches a normal operating temperature.
Monitor the HO2S voltage for the sensor that applies to this DTC with a scan tool.

Is the HO2S voltage fixed at more than the specified value?

944 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.
Measure the voltage of the HO2S high signal circuit for the HO2S that applies to this DTC with a DMM.

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 reference circuit at the engine side.
Turn ON the ignition, with the engine OFF.
Observe the voltage of the affected sensor with a scan tool.

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 voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

Test the HO2S low reference 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 11

Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.

The HO2S is detecting a rich exhaust condition or may be contaminated. Inspect for one of the following conditions:

•	Any water intrusion into the HO2S connector

•	A silicon contaminated HO2S

•	The engine oil contaminated by fuel

•	An EVAP canister purge condition

•	An incorrect fuel pressure

•	A leaking fuel pressure regulator

•	Any rich 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 10

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 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .

Did you complete the replacement?

Go to Step 13

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

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 13

Clear the DTCs with a scan tool.
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 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