For 1990-2009 cars

### 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 P0133: HO2S Slow Response Sensor 1
DTC P1133: HO2S Insufficient Switching Sensor 1

### Diagnostic Fault Information

#### HO2S 1

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S Signal | P0131, P0171 | P0132, P0134, P0137, P2A00 | P0132, P0134 | P0133, P1133, P2A00
Low Reference | -- | P0134, P0137 | -- | P0133, P1133, P2A00

#### HO2S 2

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S Signal | P0137 | P0138, P0140 | P0138, P0140 | --
Low Reference | -- | P0138, P0140 | -- | --

### Circuit 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. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,275 mV. 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 toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases 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.

### Conditions for Running the DTC

• | DTCs P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0134, P0201, P0202, P0203, P0204, P0300, P0315, P0335, P0336, P0442, P0443, P0446, P0449, P0451, P0452, P0453, and P0496 are not set.

• | The calculated airflow into the engine is between 10-45 g/s.

• | The engine speed is between 1,100-3,500 RPM.

• | The engine coolant temperature is greater than 60°C (140°F).

• | The BARO is greater than 70 kPa (10 psi).

• | The ignition voltage is between 10-18 volts.

• | The fuel system is in Closed Loop.

• | The evaporative emissions (EVAP) purge is less than 20 percent.

• | The EVAP purge is not changing states.

• | The engine run time is greater than 3 minutes.

• | The fuel level is greater than 10 percent.

• | The long term fuel trim is enabled.

• | The HO2S heater is enabled for greater than 40 seconds.

• | The vehicle is not decelerating.

• | The vehicle is not operating in power enrichment.

• | The DTCs run once per ignition cycle when the above conditions are met for greater than 1 second.

### Conditions for Setting the DTC

#### P0133

The ECM detects that the HO2S 1 rich-to-lean or lean-to-rich average response time is greater than a calibrated value.

#### P1133

The ECM detects that the HO2S 1 rich-to-lean counts, or the lean-to-rich counts are less than a calibrated value.

### Action Taken when the DTC Sets

• | DTC P0133 and P1133 are Type B DTCs.

• | The ECM commands open loop fuel control.

### Conditions for Clearing the MIL/DTC

DTC P0133 and P1133 are Type B DTCs.

### 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. Observe the DTC information with a scan tool. Verify there are no other HO2S or fuel trim DTCs set.

⇒ | If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Observe the DTC information with a scan tool. DTCs P0133 or P1133 should not set.
3. 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 you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Verify none of the following conditions exist:

• | Lean or rich fuel injectors--Refer to Fuel Injector Balance Test with Special Tool.

• | Water intrusion in the HO2S harness connector

• | Low or high fuel system pressure--Refer to Fuel System Diagnosis.

• | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

• | Fuel saturation of the evaporative emission (EVAP) canister

• | Exhaust leaks near the HO2S

• | Engine vacuum leaks

• | Engine oil consumption--Refer to Oil Consumption Diagnosis

• | Engine coolant consumption--Refer to Loss of Coolant

⇒ | If you find any of the above conditions, repair as necessary.

2. If all conditions test normal, test or replace the appropriate HO2S.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Caution: When replacing the HO2S perform the following:

• | A code clear with a scan tool, regardless of whether or not a DTC is set

• | HO2S heater resistance learn reset with a scan tool, where available

Perform the above in order to reset the HO2S resistance learned value and avoid possible HO2S failure.

• | Heated Oxygen Sensor 1 Replacement

• | Heated Oxygen Sensor 2 Replacement

• | Control Module References for ECM replacement, setup, and programming