GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 XLR 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 DTC P0031, P0037, P0051, or P0057

Circuit Description

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature and provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide current to the heater elements. The ECM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM continuously monitors the HO2S heater operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage of approximately 4.5 volts is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, when the low side driver is commanded OFF the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is lower than 2.6 volts when the heater is commanded OFF, the following DTCs will set:

    • DTC P0031 for HO2S bank 1 sensor 1
    • DTC P0037 for HO2S bank 1 sensor 2
    • DTC P0051 for HO2S bank 2 sensor 1
    • DTC P0057 for HO2S bank 2 sensor 2

Conditions for Running the DTC
    • The engine is running.
    • The Ignition 1 Signal parameter is more than 10 volts.

Conditions for Setting the DTC

The ECM detects that the HO2S heater low control circuit voltage is below 2.6 volts when the heater is commanded OFF, indicating an HO2S heater circuit shorted to ground.

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

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?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Store the Freeze Frame/Failure Records.
  2. Clear the DTCs with a scan tool.
  3. Start the engine.
  4. Observe the DTC info parameter with a scan tool for at least 30 seconds.

Does the DTC fail this ignition?

Go to Step 4

Go to Step 3

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).
  3. Connect a test lamp between the HO2S ignition 1 voltage circuit and the HO2S heater low control circuit on the engine harness side connector.
  4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step 5

Go to Step 6

5

Test the affected HO2S heater low control circuit for a short to ground or a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 7

6

Test for poor connections and shorted terminals 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 10

Go to Step 8

7

Test for poor connections and shorted terminals 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 10

Go to Step 9

8

Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .

Did you complete the replacement?

Go to Step 10

--

9

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 10

--

10
  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 11

11

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