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 Descriptor

DTC P0133: HO2S Slow Response Sensor 1

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S Bank 1 Sensor 1 Signal | P0131 | P0134 | P0132 | P0133
HO2S Bank 1 Sensor 2 Signal | P0137 | P0140 | P0138 | --
Low Reference | -- | P0134 | P0134, 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. 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.

### Conditions for Running the DTCs

• | DTC P0030, P0031, P0032, or P0036 are not set.

• | The engine speed is between 1,600-2,840 RPM.

• | The engine load is between 30-65 percent.

• | The exhaust temperature is greater than 450°C (842°F).

• | The HO2S 1 heater diagnostics have been completed.

• | DTC P0133 runs once an ignition cycle when the above conditions are met.

### Conditions for Setting the DTCs

The ECM detects that the HO2S 1 lean-to-rich average response time or the HO2S 1 rich-to-lean average response time is greater than 3 seconds.

### Action Taken when the DTCs Set

DTC P0133 is a Type B DTC.

### Conditions for Clearing the MIL/DTCs

DTC P0133 is a Type B DTC.

### 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 running, observe the DTC Information with a scan tool. Verify other DTCs are not set.

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

2. Engine running, observe the scan tool HO2S voltage parameter. The voltage should fluctuate above and below the range of 350-550 mV.
3. Operate the vehicle within the conditions for running the DTC. DTC P0133 should not set.
4. 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 or Fuel Injector Balance Test with Tech 2 .

• | Water intrusion in the HO2S harness connector

• | HO2S wiring harness damage

• | Incorrect RTV sealant

• | 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

• | Engine coolant consumption

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

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor 1 Replacement

• | Control Module References for engine control module replacement, setup, and programming