GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 SRX 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 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 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 that is shorted to ground, DTC P0131 will set for bank 1 sensor 1, or DTC P0151 will set for bank 2 sensor 1.

Conditions for Running the DTC
    • DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0132, P0133, P0135, P0137, P0138, P0139, P0140, P0141, P0152, P0153, P0155, P0157, P0158, P0159, P0160, P0161, P1137, P1138, P1157, P1158, P2231, P2234, P2237, P2240, P2243, P2247, P2251, P2254, P2626, P2629, P167A, P167B are not set.
    • The engine is running.

Conditions for Setting the DTC

The ECM detects a short to ground in one of the following HO2S circuits:

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

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-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

If DTCs P2251 or P2254 are also set, diagnose those DTCs first.

Is DTC P2251 or P2254 also set?

--

Go to DTC P2251 or P2254

Go to Step 3

3
  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 HO2S Bank 1 Sensor 1 or HO2S Bank 2 Sensor 1 parameter with a scan tool.

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

--

Go to Step 4

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records 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. 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 5

Go to Intermittent Conditions

5
  1. Turn OFF the ignition.
  2. Inspect the exhaust system for any leaks upstream from the affected heated oxygen sensor (HO2S).
  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 22

Go to Step 6

6
  1. Disconnect the connector for the HO2S 1 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 1 connectors
    • Damaged wiring
  3. Repair as necessary. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 7

7
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the HO2S Bank 1 Sensor 1 or HO2S Bank 2 Sensor 1 parameter with a scan tool.

Does the lambda value exceed the specified value?

1.115

Go to Step 12

Go to Step 8

8

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 less than the specified value?

500 mV

Go to Step 13

Go to Step 9

9

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 less than the specified value?

500 mV

Go to Step 14

Go to Step 10

10
  1. Connect a 3-amp fused jumper wire between the HO2S low reference circuit and the HO2S reference voltage circuit on the engine harness side.
  2. 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 less than the specified value?

500 mV

Go to Step 15

Go to Step 11

11
  1. Turn OFF the ignition.

    2. Important: Disconnecting the engine control module (ECM) may eliminate a circuit short.

  2. Disconnect the ECM.
  3. Test for continuity between any circuits of the affected HO2S and all other circuits of the affected HO2S.

Is the resistance between any HO2S circuit and all other HO2S circuits less than the specified value?

∞

Go to Step 19

Go to Step 16

12

Test the HO2S input pump current circuit for a short to ground. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

13

Test the HO2S reference voltage circuit for a short to ground. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

14

Test the HO2S low reference circuit for a short to ground. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

15

Test the HO2S output pump current circuit for a short to ground. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

16

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

    • HO2S connector water intrusion
    • A silicon-contaminated HO2S
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    • Lean fuel injectors
    • 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 22

Go to Step 17

17

Test for poor connections and shorted terminals at the affected HO2S. 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 22

Go to Step 20

18

Test for poor connections and shorted terminals at the harness connector of the ECM. 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 22

Go to Step 21

19

Repair the short between the affected HO2S circuits. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 22

--

20

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 22

--

21

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 22

--

22
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 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 23

23

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK