GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The powertrain control module (PCM) uses a three-way catalytic converter to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction that oxidizes the HC and CO present in the exhaust gas. After undergoing oxidation, the HC and CO are converted into harmless water vapor and carbon dioxide. The catalyst also reduces NOx emissions by converting the NOx into nitrogen. The PCM uses the heated oxygen sensors (HO2S) 1 and 2 to monitor this process. HO2S 1 produces an output signal that indicates how much oxygen is present in the exhaust gas entering the three-way catalytic converter. HO2S 2 produces an output signal that indicates the oxygen storage capacity of the catalyst. The oxygen storage capacity of the catalyst is a measure of the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than the HO2S 2 signal. If the HO2S 2 signal voltage remains excessively low for an extended period of time, DTC P0137 will set.

Conditions for Running the DTC

    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0410, P0412, P0418, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, or P1441 are not set.
    • The system voltage is more than 9 volts and less than 18 volts.
    • The Closed Loop commanded air-to-fuel ratio is between 14.4-14.9.
    • The throttle angle is between 3-40 percent.

Conditions for Setting the DTC

The HO2S 2 signal voltage remains below 175 mV during normal Closed Loop operation.

OR

The HO2S 2 signal voltage remains below 600 mV during Power Enrichment Mode fuel control operation.

Either one of these condition exists for up to 50 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

Notice: Use the connector test adapter kit J 35616-A for any test that requires probing the following items:

   • The PCM harness connectors
   • The electrical center fuse/relay cavities
   • The component terminals
   • The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.

Inspect for the following conditions

    • Misrouted heated oxygen sensor wiring--The HO2S pigtail may be mispositioned and contacting the exhaust system.
    • Faulty PCM to engine grounds--Refer to Power Distribution Schematics in Wiring Systems.
    • Incorrect fuel pressure--A condition that causes a lean exhaust can cause DTC P0137 to set. The system will go lean if the fuel pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure falls too low, DTC P0137 may set. Refer to Fuel System Diagnosis .
    • Problems with the fuel injectors--Refer to Fuel Injector Solenoid Coil Test .
    • Vacuum leaks
    • Inspect for the following conditions:
       - Disconnected or damaged vacuum hoses
       - An incorrectly installed or malfunctioning crankcase ventilation valve.
       - Vacuum leaks at the throttle body, exhaust gas recirculation (EGR) valve, and intake manifold mounting surfaces
    • Exhaust leaks--An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing DTC P0137 to set. Inspect for exhaust leaks near the HO2S 2 sensor.
    • Fuel contamination--Water can be delivered to the fuel injectors. Water, even in small amounts, can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

If the problem is intermittent, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. In order to determine if the engine is operating lean during power enrichment, operate the vehicle under higher throttle, or higher acceleration, conditions, Monitor the scan tool HO2S voltage and the power enrichment parameter at the higher acceleration. A lean condition will cause the HO2S voltage to be less than 598 mV during power enrichment.

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. Operate the engine until the normal operating temperature is reached.
  2. 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 value specified?

86 mV

Go to Step 4

Go to Step 3

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.
    • HO2S connector water intrusion
    • An exhaust leak between the HO2S and the engine.
    • An intermittent lean engine condition resulting from one of the following causes:
       - Vacuum leaks
       - An incorrect or defective positive crankcase ventilation (PCV) valve or system
       - Incorrect fuel pressure
       - Lean fuel injectors
       - An inaccurate mass air flow (MAF) sensor
    • A lean engine condition during Power Enrichment operation.

Repair any of the above or similar engine conditions as necessary.

Was a condition found and repaired?

--

Go to Step 10

Go to Diagnostic Aids

4

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

Is the HO2S voltage within the value range specified?

351-551 mV

Go to Step 5

Go to Step 6

5

The HO2S may be detecting a lean exhaust condition. Inspect for one of the following conditions:

    • HO2S connector water intrusion
    • An exhaust leak between the HO2S and the engine
    • Vacuum leaks
    • An incorrect or defective PCV valve or system
    • Incorrect fuel pressure
    • Lean fuel injectors
    • An inaccurate MAF sensor

Repair any of the above or similar engine conditions as necessary.

Was a condition found and repaired?

--

Go to Step 10

Go to Step 8

6

  1. Turn the ignition OFF.
  2. Remove the jumper from the HO2S low reference circuit terminal.
  3. Disconnect the PCM connector that contains the HO2S high signal circuit.
  4. Use a DMM, in order to measure and record the resistance between the HO2S high signal circuit and ground.
  5. Measure and record the resistance between the HO2S high signal circuit and the HO2S low reference circuit.

Is infinite resistance measured on both tests?

--

Go to Step 9

Go to Step 7

7

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

Is the action complete?

--

Go to Step 10

--

8

Replace the HO2S. Refer to Heated Oxygen Sensor 2 Replacement .

Is the action complete?

--

Go to Step 10

--

9

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 10

--

10

  1. Use a 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 11

Go to Step 2

11

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