GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 DTC P0141 or P0161

Circuit Description

The heated oxygen sensor (HO2S) produces a voltage that varies between 100-900 mV under normal operating conditions. The engine control module (ECM) produces a bias voltage on the HO2S signal circuit of 420-480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the Closed Loop operation. If the ECM detects that the HO2S internal resistance remains above a specified threshold for longer than a predetermined amount of time, DTC P0141 will set for bank 1 sensor 2, or DTC P0161 will set for bank 2 sensor 2.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC P0141 HO2S Heater Performance Bank 1 Sensor 2
    • DTC P0161 HO2S Heater Performance Bank 2 Sensor 2

Conditions for Running the DTC
    • DTCs P0021, P0024, P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0134, P0135, P0137, P0138, P0139, P0140, P0141, P0151, P0152, P0154, P0155, P0157, P0158, P0159, P0160, P0161, P0201-P0208, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0279, P0280, P0282, P0283, P0300, P0301-P0308, P0335, P0336, P0340, P0341, P0345, P0346, P0351-P0358, P0365, P0366, P0390, P0391, P0442, P0443, P0446, P0449, P0453, P0454, P0455, P0458, P0459, P0496, P2231, P2234, P2237, P2240, P2243, P2247, P2251, P2254, P2626, and P2629 are not set.
    • The Engine Speed parameter is more than 500 RPM.
    • The battery voltage is more than 10 volts.
    • The Engine Run Time parameter is more than 3 minutes.
    • The HO2S Bank 1 Sensor 2 or HO2S Bank 2 Sensor 2 heater parameter is 1-99 percent.
    • DTC P0141 or P0161 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The HO2S resistance is greater than 1,100 ohms for more than 1 minute.

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. Allow the engine to reach normal operating temperature. Refer to Scan Tool Data List .
  2. Quickly cycle the throttle from closed throttle to wide open throttle (WOT), 3 times within 5 seconds while observing the HO2S Bank 1 Sensor 2 or HO2S Bank 2 Sensor 2 parameter, with a scan tool.
  3. Observe the HO2S Bank 1 Sensor 2 or HO2S Bank 2 Sensor 2 parameter with a scan tool.

Does the voltage react immediately when performing 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 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 4

Go to Intermittent Conditions

4
  1. Turn OFF the ignition.
  2. Disconnect the affected heated oxygen sensor (HO2S) 2.
  3. Connect a 3-amp fused jumper wire between the HO2S high signal circuit, on the engine harness side connector, and a good ground.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the affected HO2S parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 5

Go to Step 7

5
  1. Remove the jumper wire from the previous step.
  2. Connect a 3-amp fused jumper wire between the HO2S high signal circuit and the HO2S low signal circuit, on the engine harness side connector.
  3. Observe the affected HO2S 2 parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 6

Go to Step 8

6
  1. Remove the jumper wire from the previous step.
  2. Measure the resistance of the following circuits with a DMM:
    3. • The HO2S heater low control circuit
    • The ignition 1 voltage circuit
    • Refer to Circuit Testing in Wiring Systems.

Is the resistance of either circuit more than the specified value?

5 ohms

Go to Step 11

Go to Step 9

7

Test the HO2S high signal circuit for an open or high resistance. 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 14

Go to Step 10

8

Test the HO2S low signal circuit for an open or high resistance. 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 14

Go to Step 10

9

Test for intermittent and poor connections at the 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 14

Go to Step 12

10

Test for intermittent and poor connections at the engine control module (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 14

Go to Step 13

11

Repair the circuit with high resistance. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 14

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12

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 14

--

13

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 14

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14
  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 15

15

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