GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0138 or P0158

Circuit Description

The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The PCM monitors and stores the heated oxygen sensor (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 majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a DTC sets.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P121, P0122, P0123, P0200, P0300, P0410, P0440, P0442, P0446, P0452, P0453, P1258, P1415, P1416, or P1441 are not set.
    • The ignition 1 signal is between 9-18 volts.
    • The loop status is Closed.
    • The secondary air injection (AIR) and the catalyst diagnostics are not active.
    • The throttle position (TP) is between 3-70 percent.
    • The air fuel ratio is between 14.5-14.7 percent.
    • The fuel tank level remaining is more than 10 percent.

Conditions for Setting the DTC
    • The HO2S signal voltage remains above 930 mV.
    • The conditions are present for 198 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: 

   • Before you service the PCM, remove any debris from the PCM connector surfaces. Inspect the PCM connector gaskets when you diagnose or replace the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.
   • For any test that requires probing the PCM or probing the component harness connectors, use the J 35616 connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Wiring Systems.

Inspect the following components for the following conditions:

    • The HO2S electrical connections--Inspect the HO2S electrical connections for evidence of water intrusion. Water present in the connector causes the B+ supply to the heater to bleed over to the signal circuit.
    • The fuel pressure--The system goes rich if the pressure is too high. The PCM compensates for some increase. If the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis .
    • Rich injectors--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool .
    • Leaking injectors--Refer to the Fuel System Diagnosis .
    • The evaporative emissions (EVAP) canister purge--Inspect for fuel saturation. If the canister is full of fuel, inspect the canister control and inspect the hoses. Refer to Evaporative Emission Control System Description .
    • The MAF sensor--Disconnect the MAF sensor and see if the rich condition is corrected. If the condition is corrected, , inspect for proper installation. If the sensor is properly installed, replace the MAF sensor. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows that indicate the proper air flow direction. The arrows must point toward the engine.
    • The 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 connections for breaks or for contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.
    • The TP sensor--An intermittent TP sensor output causes the system to go rich, due to a false indication of engine acceleration.

For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. This DTC also sets during a deceleration fuel cut-off. Inspect for conditions which could cause a rich exhaust during a deceleration. These conditions include leaking injectors and stuck injectors.

    Before you perform this test, the engine must be at the normal operating temperature.

  2. The Freeze Frame/Failure Records may help to locate an intermittent condition. If you cannot duplicate the DTC, the information in the Freeze Frame/Failure Records can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also help to determine how many ignition cycles have occurred since the diagnostic reported a pass and/or a fail. In order to isolate when the DTC failed, operate the vehicle within the same Freeze Frame conditions that you observed. These conditions include the RPM, the vehicle load, the vehicle speed, and the temperature.

    3.

  3. If the voltage remains high, the HO2S high signal circuit is shorted to a voltage. If the voltage goes low, a rich condition exists.

    4.

  4. This step isolates the condition. If the voltage remains high, the HO2S high signal circuit is not shorted to the heater ignition voltage circuit.

    5.

  5. Test for a short between the HO2S high signal circuit and any other wires that are powered by this fuse and that run together inside the harness.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to

Diagnostic System Check - Engine Controls

2

  1. Start and run the engine until normal operating temperature is reached.
  2. With a scan tool, observe the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage more than the specified value?

930 mV

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame/Failure records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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

4

  1. Turn OFF the ignition.
  2. Disconnect the HO2S connector for the sensor that applies to this DTC.
  3. Jumper the HO2S low signal circuit terminal on the engine harness side to a known good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Use a scan tool in order to observe the HO2S voltage.

Is the HO2S voltage within the specified range?

350-550 mV

Go to Step 5

Go to Step 6

5

  1. The HO2S may be detecting a rich exhaust condition or may be contaminated. Inspect for the following conditions:
    2. • Water intrusion into the HO2S connector
    • Silicone contamination of the HO2S
    • Engine oil contaminated by fuel
    • Incorrect fuel pressure
    • Rich fuel injectors
    • Inaccurate MAF sensor
    • EVAP canister purge condition
  2. Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 7

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector that contains the HO2S high signal circuit. Refer to Powertrain Control Module Replacement
  3. Turn ON the ignition, with the engine OFF.
  4. 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 11

Go to Step 8

7

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 11

Go to Step 9

8

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 11

Go to Step 10

9

Replace the affected 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 11

--

10

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

--

11
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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 12

Go to Step 2

12

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