GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Catera 🢒 Engine 🢒 Engine Controls - 3.0L (L81) 🢒 DTC P0131 or P0151

Circuit Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust stream more quickly and accurately than the switching style HO2S. The wide range HO2S sensor functions more like an air fuel sensor. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a signal voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant signal voltage. The ECM monitors the voltage variation on the signal circuit and attempts to keep the voltage constant by increasing or decreasing the amount of current flow or reversing the direction of the current flow to the pumping cell. By measuring the direction and amount of current required to maintain the signal voltage, the ECM can determine the concentration of oxygen in the exhaust. The signal voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the oxygen level is low, the lambda signal will be low or less than 1. The ECM uses this information to maintain the proper air/fuel ratio.

Conditions for Running the DTC
    • DTCs P0300, P0306, P0171, P0172, P0174, P0175, P0440, P0442, P0443, P0446, P0455, or P0460 are not set.
    • The engine is at the operating temperature.
    • The engine speed must be between 1,400-2,400 RPM.
    • The engine load is 8-12 percent.
    • The mass air flow (MAF) 18-22 g/s.
    • The throttle position (TP) is 6-10 percent.
    • The secondary air diagnosis is not running.
    • The Closed Loop fuel control has not reached maximum or minimum.
    • Evaporative emissions (EVAP) high loading is not indicated.

Conditions for Setting the DTC

The ECM has determined that the HO2S does not respond as expected.

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
    • Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
    • This DTC is most likely to set by a blocked passage that does not allow the exhaust gas to pass through the sensor. Check for any sign of contamination and for the source of the contamination.
    • Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Inspect the HO2S 1 harness for any signs of high resistance or shorts to ground. Use a DMM if necessary.
    • An open fuse in the HO2S heater circuit may be caused by the heater element in one of the sensors. The condition may not be present until the heater operates for a period of time. If no fault is present in the heater circuit, monitor the amperage of each heater using the DMM to determine if one of the heater elements is the cause of the open fuse.

Test Description

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

  1. Multiple DTCs will set if the supply voltage to the sensor heaters is open.

    2.

  2. Any exhaust leak, even a small one, can affect the operation of the HO2S. The ECM compares the reading of sensor 1 with the reading of sensor 2 as part of the diagnosis. A leak between sensor 1 and sensor 2 may set a diagnostic trouble code (DTC).

    3.

  3. The test lamp may illuminate or flash depending on the operating conditions. This indicates the ECM and the control circuit are functioning. The engine must be running for the ECM to operate the control circuit.

    4.

  4. A short between the signal circuit and the reference ground circuit or the pump current input and output circuits may not appear on the voltage tests. The ECM must be disconnected and each circuit tested for continuity with the other HO2S circuits.

P0131 or P0151 Heated Oxygen Sensor (HO2S) Heater Circuit Sensor 1

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

Using the scan tool, observe the DTC information.

Are DTCs P0135, P0141, P0155, P0161, P1141 or P1161 set?

--

Go to Step 3

Go to Step 4

3
  1. Turn OFF the ignition.
  2. Inspect fuse 43 for the oxygen sensor heaters located in the ECM housing.

Is fuse 43 open?

--

Go to Step 19

Go to Step 20

4

  1. Inspect the exhaust system for any leaks upstream from the affected oxygen sensor.
  2. Inspect for any exhaust leaks between sensor 1 and sensor 2.
  3. Repair the exhaust leak as necessary.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 5

5

Important: The ignition must be OFF when disconnecting or connecting the HO2S electrical connector.

  1. Turn OFF the ignition.
  2. Disconnect the HO2S electrical connector.
  3. Inspect both halves of the connector for any signs of corrosion or contamination.

Did you find the condition?

--

Go to Step 21

Go to Step 6

6
  1. Turn ON the ignition, with the engine OFF.
  2. Using a test lamp connected to ground, probe the switched B+ circuit at the ECM side of the oxygen sensor connector.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 23

7
  1. Turn OFF the ignition.
  2. Connect a test lamp between the switched B+ circuit and the heater control circuit at the ECM side of the oxygen sensor connector.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 9

8
  1. Turn OFF the ignition.
  2. Disconnect the ECM electrical connector C1.
  3. With the test lamp still connected between the switched B+ and the control circuit, turn ON the ignition.

Does the test lamp illuminate?

--

Go to Step 22

Go to Step 26

9

  1. Start and idle the engine.
  2. Observe the test lamp.

Does the test lamp illuminate or flash?

--

Go to Step 10

Go to Step 18

10
  1. Turn OFF the ignition.
  2. Remove the test lamp.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage of the HO2S signal circuit at the ECM side of the connector to battery ground.

Is the voltage within the specified range?

2-4 V

Go to Step 11

Go to Step 15

11

Measure the voltage of the HO2S reference ground circuit at the ECM side of the connector to battery ground.

Is the voltage within the specified range?

2-4 V

Go to Step 12

Go to Step 15

12

Measure the voltage of the HO2S pump current input circuit at the ECM side of the connector to battery ground.

Is the voltage within the specified range?

0.2-0.4 V

Go to Step 13

Go to Step 15

13

Measure the voltage of the HO2S pump current output circuit at the ECM side of the connector to battery ground.

Is the voltage within the specified range?

0.2-0.4 V

Go to Step 14

Go to Step 15

14

  1. Turn OFF the ignition.
  2. Disconnect the ECM connector C1.
  3. Test each of the circuits on the affected HO2S for a short to each other.
  4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 24

15

Is the voltage more than the specified value?

0.4 V

Go to Step 17

Go to Step 16

16
  1. Test the affected circuit for the following conditions:
    2. • Open
    • Short to ground
    • High resistance
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 25

17
  1. Test the affected circuit for a short to voltage.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 25

18
  1. Turn OFF the ignition.
  2. Disconnect the ECM connector C1.
  3. Test the heater control circuit for the following conditions:
    4. • Open
    • High resistance
    • Short to voltage
  4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 25

19
  1. Test the switched B+ circuit for a short to ground.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Diagnostic Aids

20

Locate and repair the open in the switched B+ circuit from the Engine Controls Power Relay to the splice for the oxygen sensors. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

21

Repair or replace the terminal as necessary. Refer to Connector Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

22

Repair the short to ground in the heater control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

23

Repair the open in the B+ circuit from the splice to the oxygen sensor. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 27

--

24

Replace the HO2S. Refer to Heated Oxygen Sensor Replacement .

Did you complete the replacement?

--

Go to Step 27

--

25
  1. Test for a poor connection or poor terminal tension at the ECM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 27

Go to Step 26

26

Important: 

   • Perform the idle learn procedure when replacing the ECM.
   • This vehicle is equipped with a theft deterrent system that interfaces with the ECM. Program the new ECM with the frequency code of the theft deterrent module that is currently in the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the action?

--

Go to Step 27

--

27
  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 28

Go to Step 2

28

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