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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2008 🢒 LaCrosse 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 DTC P0137, P0138, or P0140

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0137: HO2S Circuit Low Voltage Sensor 2

DTC P0138: HO2S Circuit High Voltage Sensor 2

DTC P0140: HO2S Circuit Insufficient Activity Sensor 2

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

HO2S 2 Signal

P0137, P2096

P0140

P0138

--

HO2S 2 Low Reference

--

P0140

--

--

Circuit Description

The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The ECM monitors and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The ECM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.

Conditions for Running the DTCs

P0137

    • DTCs P0117, P0118, P0119, and P0128 are not set.
    • The engine is operating for greater than 1 second.
    • The HO2S 2 heater is at operating temperature for greater than 90 seconds.
    • The ignition voltage is greater than 11 volts.
    • The engine coolant temperature (ECT) is less than 40°C (104°F) at start-up and the ECT was greater than 60°C (140°F) when the ignition was turned OFF last ignition cycle.
    • DTC P0137 runs continuously once the above conditions are met.
        OR
    • The engine is operating for greater than 1 second.
    • The HO2S 2 heater is at operating temperature for greater than 90 seconds.
    • The ignition voltage is greater than 11 volts.
    • The commanded lambda is greater than 1.006
    • DTC P0137 runs continuously once the above conditions are met for greater than .

P0138 or P0140

    • The engine is operating.
    • The HO2S heater is at operating temperature for greater than 90 seconds.
    • The ignition voltage is greater than 11 volts.
    • The calculated exhaust temperature is less than 800°C (482-1,472°F).
    • DTC P0138 runs continuously once the above conditions are met for greater than 5 seconds.
    • DTC P0140 runs continuously once the above conditions are met for greater than 60 seconds.

Conditions for Setting the DTCs

P0137

    • The ECM detects that the HO2S 2 signal voltage is less than 60 mV.
    • The condition exists for greater than 4 seconds, or for a cumulative of 50 seconds.

P0138

    • The ECM detects that the HO2S 2 signal voltage is greater than 1,150 mV.
    • The condition exists for greater than 4 seconds, or for a cumulative of 50 seconds.

P0140

    • The ECM detects that the HO2S 2 voltage is between 400-548 mV.
        OR
    • The ECM detects that the measured internal resistance of the HO2S is greater than 40,000 ohms, when the calculated exhaust temperature is greater than 450°C (842°F).
    • Either condition exists for greater than 4 seconds, or for a cumulative of 50 seconds.

Action Taken when the DTCs Set

DTCs P0137, P0138, and P0140 are Type B DTCs.

Conditions for Clearing the MIL/DTCs

DTCs P0137, P0138, and P0140 are Type B DTCs.

Diagnostic Aids

The following table illustrates the ECM connector locations:

ECM Connector Location

X2

X1

Front of Vehicle

The rear HO2S will not go into Closed Loop when the engine is idling. Once the HO2S are at operating temperature, and the vehicle is moving, the rear HO2S will go into Closed Loop.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Engine idling at normal operating temperature. Observe the scan tool HO2S 2 voltage parameter. Cycle the throttle from idle to wide open throttle (WOT) 3 times within 5 seconds. Verify the HO2S 2 voltage parameter goes above, or below 350-550 mV.
  2. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the HO2S 2.
  2. Ignition ON, test for 350-550 mV between the high signal circuit terminal B and ground.
    3. ⇒If less than the specified range, test the high signal circuit for a short to ground, or an open/high resistance. If the circuit tests normal, replace the ECM.
    ⇒If greater than the specified range, test the high signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  3. Connect a 3A fused jumper wire between the high signal circuit terminal B and the low signal circuit terminal A. Verify the scan tool HO2S 2 parameter is less than 10 mV.
    4. ⇒If greater than the specified range, test the low signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  4. If all conditions test normal, replace the HO2S 2.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Heated Oxygen Sensor 2 Replacement
    •  Control Module References for engine control module replacement, setup, and programming