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 P2195: HO2S Signal Biased Lean Bank 1 Sensor 1
DTC P2197: HO2S Signal Biased Lean Bank 2 Sensor 1

### Circuit Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or greater than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio. If the ECM detects that the HO2S signal voltage is low, this DTC sets.

### Conditions for Running the DTC

• | The engine is operating.

• | The front and rear heated oxygen sensors are at operating temperature.

• | The engine is running in closed loop.

• | DTCs P2195 and P2197 run continuously once the above conditions are met.

### Conditions for Setting the DTC

The ECM detects that an HO2S 1 is operating too lean while the corresponding HO2S 2 is operating too rich and the ECM detects that the fuel trim is at maximum control.

OR

The ECM detects that an HO2S 2 is operating too rich while the ECM is commanding a lean air/fuel mixture.

### Action Taken When the DTC Sets

DTCs P2195 and P2197 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2195 and P2197 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. Ignition ON, observe the scan tool DTC information. Verify DTCs P0137, P0138, P0140, P0157, P0158, or P0160 is not set.

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

Caution: Refer to Road Test Caution in the Preface section.

Important: The rear heated oxygen sensor (HO2S) must be in closed loop for this diagnostic to run. A road load condition is necessary to obtain closed loop.

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 you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Verify that none of the following conditions exist:

• | Inspect the appropriate HO2S 1 and HO2S 2 for being secure

• | Damaged wiring between either HO2S and the ECM

• | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2.

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

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

• | Contaminated HO2S-Silicon

• | Engine vacuum leaks

• | Exhaust leaks near either HO2S

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

2. Ignition OFF, disconnect the harness connector at the appropriate HO2S 2.
3. Ignition ON, verify the scan tool HO2S 2 voltage parameter is between 350-550 mV

⇒ | If less than the specified range, test the HO2S 2 high signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.

4. Connect the harness connector at the HO2S 2.
5. Engine idling, raise the engine speed above 1,200 RPM for 30 seconds. Verify the scan tool HO2S 2 voltage parameter is greater than 60 mV.

⇒ | If less than the specified range, replace the HO2S 2.

6. Engine idling, move the HO2S 1 and HO2S 2 harnesses between the HO2S harness connector and the ECM. Observe the scan tool HO2S 1 lambda parameter, and the HO2S 2 voltage parameter. Verify the parameters do not change abruptly.

⇒ | If the parameter changes abruptly, repair the harness/connections as necessary.

7. If all circuits/connections test normal, replace the appropriate HO2S 1.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

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