GM Service Manual Online
For 1990-2009 cars only

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 provide an overview of each diagnostic category.

DTC Descriptor

DTC P0133: HO2S Slow Response Sensor 1

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

HO2S Sensor 1 Signal

P0131

P0131

P0132

P0133

HO2S Sensor 2 Signal

P0137

P0137

P0138

P0140

Low Reference

--

P0131, P0137

P0132, P0138

--

Typical Scan Tool Data

HO2S 1 and 2

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: Engine operating in Closed Loop

Parameter Normal Range: Fluctuates above and below 350-500 mV

HO2S 1 and 2 Signal

0 mV

400-415 mV

1000 mV

Low Reference

--

400-415 mV

1000 mV

Circuit/System Description

The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of about 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.

The HO2S utilizes the following circuits:

    • A signal circuit
    • A low reference circuit
    • An ignition 1 voltage circuit
    • A heater control circuit

Conditions for Running the DTC

    • DTC P0030 is not set.
    • The fuel system is in closed loop.
    • The engine control module (ECM) command of the evaporative emission (EVAP) canister purge solenoid is less than 100 percent.
    • The engine coolant temperature is more than 70°C (158°F).
    • The vehicle speed is between 65-75 km/h (40-46 mph).
    • The engine speed is between 2,144-2,464 RPM.
    • The air flow into the engine is between 23-43 kg/h.
    • The engine is operating for more than 320 seconds.
    • The DTC runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the average rich to lean response is more than 1.4 seconds or the lean to rich response is more than 0.75 second.

OR

The ECM detects a difference between the rich to lean time is more than 1 second, or the ECM detects a difference between the lean to rich time is less than 1 second.

Action Taken When the DTC Sets

DTC P0133 is a Type B DTC.

Conditions for Clearing the MIL/DTC

DTC P0133 is a Type B DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification

  1. If any other HO2S DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnose the applicable DTC
  2. Operate the vehicle within the parameters specified in Conditions for Running the DTC. DTC P0133 should not set.
  3. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

Circuit/System Testing

  1. Verify that the following conditions do not exist:
  2. • An exhaust leak near the HO2S--Refer to Symptoms - Engine Exhaust .
    • The HO2S is not securely installed.
    • Corrosion on the HO2S terminals
    • Poor terminal tension at the HO2S and at the ECM
    • HO2S wiring damage
    • Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Incorrect RTV sealant
    • Engine oil consumption--Refer to Symptoms - Engine Mechanical .
    • Engine coolant consumption--Refer to Loss of Coolant .
         ⇒If you find any of the above conditions, repair as necessary.
  3. Ignition OFF, disconnect the harness connector of the HO2S 1.
  4. Important: The test lamp is used to load the circuit and may not illuminate.

  5. Connect a test lamp between the low reference circuit of the HO2S 1 and the positive terminal of the battery.
  6. Ignition ON, test for less than 0.1 volt between the low reference circuit of the HO2S 1 and the negative terminal of the battery.
  7. If greater than 0.1 volt, test the low reference circuit of the HO2S 1 for high resistance. If the circuit/connections test normal, replace the ECM.
  8. Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S 1 and verify the HO2S parameter is less than 60 mV.
  9. If greater than 60 mV, test the signal circuit of the HO2S 1 for high resistance. If the circuit/connections test normal, replace the ECM.
  10. If all circuits/connections test normal, replace the HO2S 1.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Heated Oxygen Sensor 1 Replacement
    •  Control Module References for ECM replacement, setup, and programming