GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 DTC 🢒 DTC P0134 or P0154

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 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 value will be high, or more than 1. When the system is rich, the oxygen level is low and the lambda value will be low, or less than 1. The ECM uses this information to maintain the proper air/fuel ratio. If the ECM detects an HO2S circuit is open, DTC P0134 will set for bank 1 sensor 1, or DTC P0154 will set for bank 2 sensor 1.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC P0134 HO2S Circuit Insufficient Activity Bank 1 Sensor 1
    • DTC P0154 HO2S Circuit Insufficient Activity Bank 2 Sensor 1

Conditions for Running the DTC
    • DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0131, P0132, P0133, P0135, P0137, P0138, P0139, P0140, P0141, P0151, P0152, P0153, P0155, P0157, P0158, P0159, P0160, P0161, P1137, P1138, P1157, P1158 are not set.
    • The ignition is ON.
    • DTC P0134 or P0154 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects one of the following HO2S circuits is open for more than 1 second.

    • The input pump current
    • The output pump current
    • The reference voltage
    • The low reference

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.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Start the engine.
  2. Allow the engine to reach operating temperature. Refer to Scan Tool Data List .
  3. Cycle the throttle from idle to wide open throttle (WOT) 3 times within 5 seconds.
  4. Observe the affected heated oxygen sensor (HO2S) lambda value.

Does the affected HO2S lambda value react immediately to the above action?

--

Go to Step 3

Go to Step 4

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 90 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4
  1. Turn OFF the ignition.
  2. Inspect the exhaust system for any leaks upstream from the affected oxygen sensor.
  3. Inspect for any exhaust leaks between the HO2S 1 and the HO2S 2.
  4. Repair the exhaust leak as necessary. Refer to Exhaust Leakage in Engine Exhaust.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 5

5
  1. Disconnect the connector for the HO2S that applies to this DTC.
  2. Visually and physically inspect for the following items:
    3. • The HO2S 1 is securely installed.
    • Terminal corrosion or water intrusion
    • Terminal tension at the HO2S connectors
    • Damaged wiring
  3. Repair as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 6

6

Measure the voltage from the HO2S low reference circuit, on the engine harness side connector, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

2.4-2.7 V

Go to Step 7

Go to Step 11

7

Measure the voltage from the HO2S reference voltage circuit, on the engine harness side connector, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

2.8-3.1 V

Go to Step 8

Go to Step 12

8

Measure the voltage from the HO2S input pump current circuit, on the engine harness side connector, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage less than the specified value?

100 mV

Go to Step 9

Go to Step 13

9

Is the voltage within the specified range?

10-65 mV

Go to Step 10

Go to Step 14

10

Measure the voltage from the HO2S output pump current circuit, on the engine harness side connector, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

10-65 mV

Go to Step 16

Go to Step 15

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 20

Go to Step 17

12

Test the HO2S reference voltage 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 20

Go to Step 17

13

Important: 

   • The normal open circuit voltage of the HO2S output pump current circuit is approximately 10-65 millivolts.
   • The normal open circuit voltage of the HO2S low reference voltage circuit is 2.4-2.7 volts.

Test the HO2S output pump current circuit for a short to the HO2S low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 17

14

Test the HO2S input pump current 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 20

Go to Step 17

15

Test the HO2S output pump current 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 20

Go to Step 17

16

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

    • HO2S connector water intrusion
    • A silicon-contaminated HO2S
    • Fuel-contaminated engine oil
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    • A leaking fuel pressure regulator--Refer to Fuel System Diagnosis .
    • Rich fuel injectors
    • Lean fuel injectors--Refer to Fuel System Diagnosis .
    • An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.
    • Vacuum leaks
    • Fuel contamination--Water, even in small amounts, can be delivered to the fuel injectors. The water 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 for the proper procedure for inspecting for contaminants.
    • 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 20

Go to Step 18

17

Test for poor connections and shorted terminals at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

18

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 20

--

19

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 20

--

20
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 90 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 21

21

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK